Geology of Tasmania
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The geology of
Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...
is complex, with the world's biggest exposure of diabase, or dolerite. The rock record contains representatives of each period of the
Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...
,
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ...
,
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
and
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...
eras. It is one of the few southern hemisphere areas that were glaciated during the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
with glacial landforms in the higher parts. The west coast region hosts significant mineralisation and numerous active and historic mines.


Geological history

The earliest geological history is recorded in rocks from over . Older rocks from
western Tasmania The West Coast of Tasmania is mainly isolated rough country, associated with wilderness, mining and tourism. It served as the location of an early convict settlement in the early history of Van Diemen's Land, and contrasts sharply with the mor ...
and King Island were strongly folded and metamorphosed into rocks such as
quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...
. After this there are many signs of
glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate bet ...
from the
Cryogenian The Cryogenian (from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed ...
, as well as the
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
that occurred at the start of the
Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...
period. An
orogeny Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An '' orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted ...
folded the older
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of th ...
rocks. In the
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...
time the Tyennan block forming the
south west The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sep ...
and central Tasmania, was pushed up and slightly over the land of
north west Tasmania North West Tasmania is one of the regions of Tasmania in Australia. The region comprises the whole of the north west, including the ''North West Coast'' and the northern reaches of the ''West Coast''. It is usually accepted as extending as f ...
, the Tyennan Orogeny. Then there were volcanic action and sediments from the Cambrian and
Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...
. The large ore deposits were formed on the West Coast. The north east of Tasmania began to form as part of the
Lachlan Orogen The Lachlan Fold Belt (LFB) or Lachlan Orogen is a geological subdivision of the east part of Australia. It is a zone of folded and faulted rocks of similar age. It dominates New South Wales and Victoria, also extending into Tasmania, the Austra ...
with
turbidity flow A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. T ...
s of mud and sand on to the ocean floor. In the Devonian the Tabberabberan Orogeny caused more folding, and intrusion of
granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...
on the west and east coasts, and probably joined the east of Tasmania to the west. In the
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...
period, conditions were again glacial and the Tasmania basin formed, with low sea levels in the
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
. A giant intrusion of magma happened in the
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
forming
diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grain ...
, or dolerite which gives many of the Tasmanian mountains their characteristic appearance. Continental breakup happened in the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
and
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...
Periods, splitting off undersea plateaus, forming
Bass Strait Bass Strait () is a strait separating the island states and territories of Australia, state of Tasmania from the Australian mainland (more specifically the coast of Victoria (Australia), Victoria, with the exception of the land border across Bo ...
and ultimately breaking Tasmania away from
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
. In the Cenozoic, a couple of basins extended inland from
Macquarie Harbour Macquarie Harbour is a shallow fjord in the West Coast region of Tasmania, Australia. It is approximately , and has an average depth of , with deeper places up to . It is navigable by shallow-draft vessels. The main channel is kept clear by th ...
and the northern
Midlands The Midlands (also referred to as Central England) are a part of England that broadly correspond to the Kingdom of Mercia of the Early Middle Ages, bordered by Wales, Northern England and Southern England. The Midlands were important in the In ...
. The higher mountains were glaciated during the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
.


Precambrian

The oldest rocks in Tasmania from the Precambrian form several blocks. The blocks are King Island; Rocky Cape in the North West, Dundas Element in the mid west; Sheffield Element in the central north; Tyennan Element in the west central and south west; and the Adamsfield-Jubilee Element in the south central to south coast. The island's oldest rocks seem to have originated when that part of the island was attached to western North America. Analysis of
monazite Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...
and
zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
in rocks of the ancient Rocky Cape Group in north-west Tasmania found that they are between 1.45 billion and 1.33 billion years old. These minerals, strongly resemble those found in
Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...
,
Idaho Idaho ( ) is a U.S. state, state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Monta ...
and southern
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
. Fossils called ''
Horodyskia ''Horodyskia'' is a fossilised organism found in rocks dated from to . Its shape has been described as a "string of beads" connected by a very fine thread. It is considered one of the oldest known eukaryotes. Biology Comparisons of differe ...
'' have also been found in both sites. Importantly, at more than 1 billion years old, the fossils are some of the oldest visible to the naked eye. Previous theories had suggested that Tasmania emerged from central Australia as the supercontinents broke apart, but the recent spectroscopic and radioactive dating evidence contradicts this. Tasmania's geographic location during the Precambrian is still unclear, but it is clear that some of it was linked to an area of ancient North America. The rocks of Tasmania are much older than those of the east coast of Australia indicating a different geologic history. Alternative ideas for the location are presented
below Below may refer to: *Earth *Ground (disambiguation) *Soil *Floor *Bottom (disambiguation) *Less than *Temperatures below freezing *Hell or underworld People with the surname *Ernst von Below (1863–1955), German World War I general *Fred Below ( ...
. On King Island now in Bass Strait, the oldest Tasmanian rocks are found. On the west side of King Island, there are
basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
s that have been metamorphosed by
amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...
grade metamorphism at . Sedimentary rocks such as feldspathic sandstone that have been altered to
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
and quartzite. Detrital zircons have been dated to 1350, 1444, 1600, 1768 and 1900 Ma. A
dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grain ...
sill Sill may refer to: * Sill (dock), a weir at the low water mark retaining water within a dock * Sill (geology), a subhorizontal sheet intrusion of molten or solidified magma * Sill (geostatistics) * Sill (river), a river in Austria * Sill plate, ...
was intruded. Granite intruded in the Cryogenian. The granite contains inherited
zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
s from . The Wickham deformation affected the earlier rocks by heating to 470 to 480 °C at pressures below 300
MPa MPA or mPa may refer to: Academia Academic degrees * Master of Performing Arts * Master of Professional Accountancy * Master of Public Administration * Master of Public Affairs Schools * Mesa Preparatory Academy * Morgan Park Academy * Mou ...
, and tight folding. This was followed later in the
Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...
on the eastern side of the island with beds of
diamictite Diamictite (; from Ancient Greek ''δια'' (dia-): ''through'' and ''µεικτός'' (meiktós): ''mixed'') is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that r ...
,
dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...
,
mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.' ...
,
tholeiite The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma ...
, and
picrite Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite. The olivine-rich p ...
interleaved with
conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** ...
. Also dykes of
augite Augite is a common rock-forming pyroxene mineral with formula . The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees. Characteristics Augite is a solid solution in the pyroxene group ...
syenite Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). Some syenites contain larger prop ...
, picrite and 580 Ma tholeiite dolerite were intruded. An interpretation is that deposits occurred in a tidal area, with a
continental Continental may refer to: Places * Continent, the major landmasses of Earth * Continental, Arizona, a small community in Pima County, Arizona, US * Continental, Ohio, a small town in Putnam County, US Arts and entertainment * ''Continental'' ( ...
rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...
allowing
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
from the
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
to intrude. These newer Proterozoic sediments were then tilted and faulted. The latter tholeiite igneous rocks have a strong magnetic signature, and this can be detected from the rock underneath Bass Strait. The band of rocks is 35 km wide. It extends north northeast to Phillip Island, Victoria, and also south 40 km to just off the west coast of Tasmania stopping at the Braddon River Fault In the Rocky Cape Block west of Wynyard and north of Granville Harbour, the Precambrian rocks consist of the Rocky Cape Group from the
Stenian The Stenian Period (, from grc, στενός, stenós, meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined ...
period, with Cowrie
Siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...
, Detention Subgroup, Irby Siltstone, and Jacob Quartzite. The sequence covers most of the block and is over 5700 metres thick. Currents travelled either northwesterly or southeasterly. The metamorphic belt titled the Arthur Lineament forms the limits of the Rocky Cape Group to the south east. The Burnie Formation followed in the
Tonian The Tonian (from grc, τόνος, tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based o ...
period south east of the lineament with
greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...
and slaty mudstone, and also some basic
pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discont ...
s. The Oonah Formation has even more varieties of rock than the Burnie formation, also including conglomerate, quartz sandstone, dolomite and
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...
. The Bowry Formation in the Cryogenian was intruded by granite (Bowry granitoids) . These have been metamorphosed to the
blueschist Blueschist (), also called glaucophane schist, is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures (), approximately corresponding to a depth of . The blue ...
level. In the Smithton Synclinorium the Togari Group followed with conglomerate from the
Sturtian The Sturtian glaciation was a Snowball Earth glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined, ...
and
Marinoan glaciation The Marinoan glaciation, sometimes also known as the Varanger glaciation, was a period of worldwide glaciation that lasted from approximately 650 to 632.3 ± 5.9 Ma (million years ago) during the Cryogenian period. This glaciation possibly cover ...
s and dolomite marking the end of Cryogenian and on into the Ediacaran and Cambrian. The Togari group contains greywacke, conglomerate, diamictite, mafic volcanic rocks, and quartz sandstone, and mudstone. The components of the Togari Group are called Forest Conglomerate and Quartzite, Black River Dolomite, Kanunnah subgroup (containing the lavas) and Smithton Dolomite. These rocks are important for determining the boundary between the Cryogenian and Ediacaran periods as they contain volcanics that can be dated and dolomites marking the end of glaciations and marking the period boundary. Near
Corinna Corinna or Korinna ( grc, Κόριννα, Korinna) was an ancient Greek lyric poet from Tanagra in Boeotia. Although ancient sources portray her as a contemporary of Pindar (born ), not all modern scholars accept the accuracy of this tradition ...
the Ahrberg group is correlated with the Togari Group and the Success Creek Group. It contains the Donaldson Formation (a marine fan), Savage Dolomite which contains
stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...
s; Bernafai Volcanics containing
albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicate ...
epidote Epidote is a calcium aluminium iron sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in ...
actinolite Actinolite is an amphibole silicate mineral with the chemical formula . Etymology The name ''actinolite'' is derived from the Greek word ''aktis'' (), meaning "beam" or "ray", because of the mineral's fibrous nature. Mineralogy Actinolite is ...
chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorou ...
; Corinna Dolomite, and Tunnelrace Volcanics. Where the dolomite has been dissolved away over million of years it has left layers of very pure
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
flour, an important mineral resource. The Dundas Element lowest level starts with the Oonah Formation with greywacke, dolomite and basic volcanics. The Oonah Formation appeared between . It has three sections, Mount Bischoff
Inlier An inlier is an area of older rocks surrounded by younger rocks. Inliers are typically formed by the erosion of overlying younger rocks to reveal a limited exposure of the older underlying rocks. Faulting or folding may also contribute to the obser ...
, the Ramsay River Inlier and the Dundas Inlier. The Success Creek Group from the Cryogenian has diamictite, quartz sandstone (Dalcoath Formation), and mudstone. It includes the Renison Bell Formation named after the Renison Bell mine. The red rock member is
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
stained chert. The sediments slumped while soft forming folds and
breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...
and
mélange In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically cons ...
. They were then capped with
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
. The group is up to 1000 metres thick. The Crimson Creek Formation consists of greywacke with tholeiitic basalt. It is from 4000 to 5000 metres thick. This formation could be as late as the early Cambrian. The basalt is probably the same as mafic lavas of the Kanunnah Subgroup. The Sheffield Element extends from Wynyard past Devonport and the Asbestos Range on the north coast and as far south east as Golden Valley. It contains structural elements called Dial Range Trough, Forth Massif, Fossey Mountains Trough. The oldest Precambrian rocks are the Ulverstone Metamorphic Complex and Forth Metamorphic Complex. This is assumed to be the same age as metamorphic rocks from the Tyennan Block, at from the
Stenian The Stenian Period (, from grc, στενός, stenós, meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined ...
. This contains zircons predominantly dated , but also from 1710, 1851, the oldest being , and the youngest . The Burnie or Oonah Formation with Greywacke is possibly from the Tonian period, dated around . Slate from both the Burnie and Oonah formations is dated at . Both of these formations came from a shallow marine shelf. The Cooee Dolerite intruded the Burnie Formation at . Zircon grains in the Cooee Dolerite are from mostly . The Barrington Chert is finely laminated and has flaggy bedding. It is found in the Dial Range and Fossey Mountain Troughs, up to 1 km thick. The Motton Spilite lies on top of the chert. It consists of pillow lava, massive lava flows, sediments made from volcanic fragments, and chert breccia. The basalt is an ocean floor type. The Badger Head Inlier consists of deformed Burnie Formation. The Andersons Creek Ultramafic Complex is west of
Beaconsfield Beaconsfield ( ) is a market town and civil parish within the unitary authority of Buckinghamshire, England, west-northwest of central London and south-southeast of Aylesbury. Three other towns are within : Gerrards Cross, Amersham and High W ...
and east of the inlier with
serpentinite Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''s ...
,
pyroxenite Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the we ...
,
gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...
and a sliver of oolitic chert introduced as a fault bounded block. To the west of the Badger Head Inlier is the Port Sorell Formation, a tectonic mélange of
marine sediment Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles have their origins in soil and rocks and have been transported from the land to the sea, mai ...
s and dolerite. In the Tyennan block, the Precambrian basement that forms the central core of Tasmania there are two formations. First, the Oonah Formation contains
turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites wer ...
with quartz
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...
interbedded with siltstone deposited by gravity flows. This has been deformed with tight folds that have been overturned, and exhibits crenulation cleavage and brittle faulting. Zircons in the quartzite have peak numbers aged and . Secondly, the Scotchfire Metamorphic Complex contains quartzite deposited in the sea from windblown desert sands,
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
and
phyllite Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily compo ...
possibly from a delta. Small quantities of dolomite and boulder
conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** ...
are also included. The complex includes boudinage structure and ''en echelon''
veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...
.Kathryn Harris
"The Geology of Central Western Tasmania: Context for a Major Mineralised Province", in ''Journal of Undergraduate Science Engineering and Technology''
/ref> Phyllite near
Strathgordon Strathgordon is a rural locality in the local government area (LGA) of Derwent Valley in the South-east LGA region of Tasmania. The locality is about west of the town of New Norfolk. The 2016 census recorded a population of 15 for the state s ...
has been dated at . Metamorphism to
greenschist facies Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite, ...
occurred at around 400 °C and 300 MPa. The Franklin Metamorphic Complex is near Mount Franklin. At Raglan Range the rocks are a mixture of quartzite and knotted
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
. Metamorphism in this area was higher grade with
almandine Almandine (), also known as almandite, is a species of mineral belonging to the garnet group. The name is a corruption of alabandicus, which is the name applied by Pliny the Elder to a stone found or worked at Alabanda, a town in Caria in Asi ...
garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different ...
forming. The Collingwood area experienced the highest grade of metamorphism with garnet-mica schist, mica schist and garnet-mica-
kyanite Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks gener ...
gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...
present, and enough heat to form veins of
migmatite Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock th ...
.
Eclogite Eclogite () is a metamorphic rock containing garnet (almandine- pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, ...
and garnet amphibolite are believed to be the remains of basalt. The eclogite has been heated to 700° at 1520 MPa, a burial depth of perhaps 50 km. Metamorphism happened at the same time as the Cambrian
ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...
complexes were introduced. In the Neoproterozoic in the Jane River basin, the very thick Jane River Dolomite appeared. The Adamsfield Jubilee element is east of the Tyennan Block. It has a strip exposed on the surface that includes the Florentine Synclinorium, The Adamsfield District, the Jubilee Region, and down to the South Coast at
Precipitous Bluff Precipitous Bluff or ''PB'' is a mountain in the South West Wilderness of Tasmania located north east of New River lagoon. Geology and Geography It is visible from the South Coast Track and the Moonlight Ridge walk with a prominence of over ...
and Surprise Bay. It also underlies the Tasmania Basin across southeastern Tasmania, but not including the east coast. The subsurface structure has been studied from a few outliers, boreholes,
xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...
s, and gravity and magnetic surveys. The basement at 5 km deep is the same as the Tyennan metamorphic rocks (Scotchfire Metamorphic Complex). Its oldest exposed rocks are from the Clark Group, of pelitic rocks, some with
stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...
s, and
evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...
s, and overlaid with orthoquartzite. The Weld River Group lies above, starting with 0.5 km thickness of conglomerate and sandstone, then up to 3 km of dolomite, interbedded with sandstone, mudstone and diamictite. Glacial dropstones are found in the interbedding, suggesting Cryogenian age, however
δ13C In geochemistry, paleoclimatology, and paleoceanography ''δ''13C (pronounced "delta c thirteen") is an isotopic signature, a measure of the ratio of stable isotopes 13C : 12C, reported in parts per thousand (per mil, ‰). The measure is al ...
profiles suggest Ediacaran age instead. Gravity and magnetic studies indicate that this sort of dolomite (dense and non-magnetic) underlies Hobart and Bruny Island in a north–south strip, and also in a region west of Hobart. The Cape Sorell Block is a region of metamorphosed sediments from the
Mesoproterozoic The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), ...
, to the south of the west end of Macquarie Harbour. It is separated from
Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...
rocks by a low angle
thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...
. The Neoproterozoic rocks contain greywacke, mudstone and pillow lavas of the Lucas Creek Volcanics (matching the Crimson Creek Formation), mudstone, siltstone (matching the Success Creek Group) and dolomite (correlating with the Togari Group). South east of this is a metamorphosed belt of dolomite rich sediments correlated with the Oonah Formation. An ultramafic belt called Point Hibbs Mélange reaches the coast near Point Hibbs. This has been complexly faulted with Cambrian,
Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...
and
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...
sediments and limestone. At the end of the Precambrian uplift there were several raised blocks forming land above the sea: the Tyennan Uplift in the central and south west Tasmania, the Rocky Cape uplift in the north west, and the Forth uplift, near Forth in the north. The far north west also had uplift as probably also did some region to the east. Basins formed were the Smithton Basin, Dial Range Basin, Fossey Mountain Basin and the Adamsfield Basin.


Early Cambrian

Next an oceanic arc collided with eastern Australia. This resulted in deep oceanic crust being thrust in a sheet over the top of the Precambrian rocks. This has left behind several
ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...
complexes bounded with faults from the older rocks. These take the form of layered
pyroxenite Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the we ...
and
dunite Dunite (), also known as olivinite (not to be confused with the mineral olivenite), is an intrusive igneous rock of ultramafic composition and with phaneritic (coarse-grained) texture. The mineral assemblage is greater than 90% olivine, w ...
; layered dunite and
harzburgite Harzburgite, an ultramafic, igneous rock, is a variety of peridotite consisting mostly of the two minerals olivine and low-calcium (Ca) pyroxene (enstatite); it is named for occurrences in the Harz Mountains of Germany. It commonly contains a f ...
; and layered pyroxenite,
peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high pr ...
and
gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...
. The layering has developed sedimentary like structures including cross bedding. This has been serpentinised, with
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With ...
separating out. Several mineral deposits are associated such as
osmiridium Osmiridium and iridosmine are natural alloys of the elements osmium and iridium, with traces of other platinum-group metals. Osmiridium has been defined as containing a higher proportion of iridium, with iridosmine containing more osmium. However ...
, and
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...
. The ultrabasic rocks are rich in orthopyroxene, which is unusual, usually clinopyroxene is found in such rocks. They were formed at high temperature but low pressure. The Heazlewood Ultramafic Complex solidified at . Other ultramafic occurrences include the Cape Sorell and Serpentine Hill Complexes. As part of this collision, three exotic suites of basalt were tectonically introduced into the Dundas Block. Near
Waratah Waratah (''Telopea'') is an Australian-endemic genus of five species of large shrubs or small trees, native to the southeastern parts of Australia (New South Wales, Victoria, and Tasmania). The best-known species in this genus is ''Telopea speci ...
is a sub-alkaline basalt from an ocean floor, another is a high-magnesium
andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...
-basalt with chrome
spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals. Properties S ...
and clinoenstatite named boninitic rock after the
Bonin Islands The Bonin Islands, also known as the , are an archipelago of over 30 subtropical and tropical islands, some directly south of Tokyo, Japan and northwest of Guam. The name "Bonin Islands" comes from the Japanese word ''bunin'' (an archaic rea ...
. This magma produced the layered pyroxenite dunite in the ultramafic area. Thirdly there is a low
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...
basalt-andesite with extreme light
rare-earth element The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides ( yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...
depletion that produced the layered pyroxenite-peridotite and associated gabbro
cumulate Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group o ...
. Two kinds of basalt from the Birchs Inlet–Mainwaring River Volcanics, occur in a belt north from Veridian Point and west of the south end of
Birchs Inlet The Birchs Inlet, also spelt Birch's Inlet or Birches Inlet, is a narrow cove or coastal inlet on the south-western side of Macquarie Harbour on the west coast of Tasmania, Australia. The inlet is located within the Southwest National Park, par ...
. In the Adamsfield area The Ragged Basin Complex is a broken up formation of chert, sandstone, red mudstone and mafic magma derived rocks. The sandstone is derived from metamorphic and volcanic fragments. Ultramafic rocks are serpentinised. They are not
ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found ...
s, but instead are cumulates of heavy minerals in a shallow magma chamber. The densest mineral,
osmiridium Osmiridium and iridosmine are natural alloys of the elements osmium and iridium, with traces of other platinum-group metals. Osmiridium has been defined as containing a higher proportion of iridium, with iridosmine containing more osmium. However ...
has been concentrated and mined at Adamsfield. These rocks are
allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe. If an erosional hole is created in the nappe that is called a window (geology)">window. A klippe is a solitary ou ...
ous, meaning that they were inserted into position by tectonic processes.


Cambrian


Mount Read Volcanics

The
Mount Read Volcanics The Mount Read Volcanics is a Cambrian volcanic belt that exists in Western Tasmania. It is a complex belt due to folding, faulting and a range of tectonic events. It is a productive mineralised belt that has profitable copper-silver and gold p ...
are a 250 km long belt that is 10 to 20 km wide attached to the western edge of the Tyennan Block or eastern side of the Dundas Element. The volcanics consist of underwater eruptions interbedded with sediment. A range of lava from basic through intermediate to acid are present along with intrusions and volcanic clastics such as
breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...
and
pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
. The breccia includes pieces of andesite,
dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained ( aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyo ...
and massive
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
. The massive sulfides were formed by
hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...
s on the sea floor. These have become ore deposits for
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
, lead,
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
and
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
. The volcanics extend south to Elliot Bay. The Noddy Creek Volcanics extend north of high Rocky Point to
Macquarie Harbour Macquarie Harbour is a shallow fjord in the West Coast region of Tasmania, Australia. It is approximately , and has an average depth of , with deeper places up to . It is navigable by shallow-draft vessels. The main channel is kept clear by th ...
with pyroxene and feldspar containing andesite as lava, breccia and intrusives. The Sticht Range Beds form a sedimentary base sitting on the Tyennan Block metamorphic rocks. Parts of the volcanics were from , and the younger Tyndall Groups has a dating of . Fossils also indicate a late middle Cambrian age. Zircons in the volcanics have two age groups: matching the metamorphic rock in the Tyennan block; and without a satisfactory explanation. In the Dial Range Trough the middle Cambrian saw the deposition of the Cateena Group of conglomerate (of purple mudstone pebbles), sandstone with feldspar, mudstone and greywacke and some felsic volcanics. The age is Florian to Undillan. This was followed by the Radfords Creek Group which has a base of a conglomerate of chert and basalt fragments. The age is Boomerangian to Late Mindyallan. In the Adamsfield area the Trial Ridge Beds, Island Road Formation, and Boyd River Formation consists of conglomerate and greywacke. They contain fossils of agnostoids.


Cambrian granites

The Murchison Granite intruded east of the Mount Read Volcanics. It consists of dioritic granodiorite. Major mineral deposits were formed at Mount Lyell, Rosebery and Henty. Granite also intruded in the Cambrian at Low Rocky Point and Elliott Bay. The north west element was altered by the Tyennan Orogeny around . The Arthur Lineament was metamorphosed to phyllite, slate and
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
ose quartzite, The Burnie and Oonah Formation were folded in various ways, and the Rocky Cape Group and the Smithton Synclinorium developed cleavage texture. The Tyennan Orogeny corresponds with the first phase of the Delamerian Orogeny in
South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest o ...
and the Ross Orogeny in North
Victoria Land Victoria Land is a region in eastern Antarctica which fronts the western side of the Ross Sea and the Ross Ice Shelf, extending southward from about 70°30'S to 78°00'S, and westward from the Ross Sea to the edge of the Antarctic Plateau. I ...
, Antarctica. The Dove Granite intruded the Tyennan Block metamorphics with several small plugs in the north dated at .


Dundas Group

The Dundas group are Cambrian sedimentary beds that interfinger with the Mount Read Volcanics. They lie
unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
on the Precambrian basement. The kind of rock is sandstone, laminated mudstone and a pebble conglomerate in which the pebbles consist of quartzite, sandstone and green mudstone. The group was formed as a submarine fan. The conglomerate includes volcanic fragments where it borders the Mount Read Volcanics, indicating that it was deposited at the same time. The Huskisson Group is from the same time period. In the Smithton Synclinorium the Scopus Formation is from the same period between Boomerangian and Idamean. The rocks are
wacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or ...
and mudstone in a submarine fan with currents flowing to the north. A channel is marked by conglomerate. Most of the material came from volcanics, but also included grit from the older Precambrian rocks. The Fossey Mountains Trough contains Cambrian intermediate volcanics, and greywacke where trilobite fossils show the age as late Middle Cambrian. Boomerangian age fossils were found in
Paradise In religion, paradise is a place of exceptional happiness and delight. Paradisiacal notions are often laden with pastoral imagery, and may be cosmogonical or eschatological or both, often compared to the miseries of human civilization: in para ...
.


Ordovician

During the
Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...
Tasmania was near the equator and was joined to
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...
. The Tyennan Block was uplifted with the Great Lyell Scarp as an
active fault An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...
. The Ordovician Wurawina supergroup comprises the Denison Group and the Gordon group. The Owen Conglomerate, part of the Denison group, lies conformably on the Dundas Group, but unconformably on the Mount Read Volcanics. The pebbles include quartz, quartzite, quartz sandstone, pale pink mudstone and chert, embedded in a matrix of sand. The Owen Group rocks are found on the
West Coast Range The West Coast Range is a mountain range located in the West Coast region of Tasmania, Australia. The range lies to the west and north of the main parts of the Franklin-Gordon Wild Rivers National Park. The range has had a significant nu ...
. The conglomerate was derived from the highlands of the uplifted Tyennan Block and is up to 1500 meters thick. The lowest section is the Jukes Conglomerate, with Lower Owen Conglomerate and Middle Owen Conglomerate above. Upper Owen Sandstone is found in Queenstown, it formed while the Great Lyell Fault was active, resulting in folding of the lower parts. The Pioneer Beds are the top layer, containing
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...
and
chromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can ...
. Correlated rocks also occur in a syncline south west of Birchs Inlet, around the upper part of the Wanderer River, and in the Dial Range Trough the equivalent unit is called the Duncan Conglomerate. The Duncan Conglomerate has pebbles mostly of chert, but also some of quartzite, hematite and lava. On the west side of the Dial Range trough at
Penguin Penguins (order Sphenisciformes , family Spheniscidae ) are a group of aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: only one species, the Galápagos penguin, is found north of the Equator. Highly adap ...
the Beecraft Megabreccia sits on top of the Burnie Formation. It consists of blocks of chert up to 120 metres long, embedded in conglomerate. The Teatree Point Megabreccia is similar and about 150 metres thick. The Lobster Creek Volcanics is actually an intrusion of plagioclase pyroxene hornblende porphyry dated at . Conglomerate and sandstone in the Fossey Mountains Trough is exposed in a band on Black Bluff Range, Mount Roland, and Gog Range. Another band runs through Saint Valentines Peak, Loyetea, Gunns Plains to the
Dial Range The Dial Range is a small mountain range in northwest Tasmania, south of the town of Penguin near the coast. It extends about north to south and 4-5 km west to east. It is bordered on the east and south by the Leven River, with the Gunns Plai ...
. On top of this is sandstone, a dolerite sill, and basalts altered to
chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorou ...
and
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
. These units are called the Roland Conglomerate and Moina Sandstone and represent contrasting stratigraphic architecture to that observed in western Tasmania, a reflection of evolution of different rift depocentres. The Gordon limestone belongs to the Gordon group. It is formed over
western Tasmania The West Coast of Tasmania is mainly isolated rough country, associated with wilderness, mining and tourism. It served as the location of an early convict settlement in the early history of Van Diemen's Land, and contrasts sharply with the mor ...
and is conformable on the Owen Conglomerate and lies unconformably over the Precambrian rocks north of Zeehan. The limestone occurs in the Dundas and Sheffield Elements and the Florentine Synclinorium. The conditions of its formation were in or near the intertidal zone. The time of its formation was between early
Caradoc Caradoc Vreichvras (; Modern cy, Caradog Freichfras, ) was a semi-legendary ancestor to the kings of Gwent. He may have lived during the 5th or 6th century. He is remembered in the Matter of Britain as a Knight of the Round Table, under the ...
and mid
Ashgill Ashgill is a village in South Lanarkshire, Scotland near Larkhall. It is part of the Dalserf parish. The village church dates back to 1889 The village has a shop The local school was first in Scotland to have an automated bell, installed in 1 ...
. A type section is at
Mole Creek Mole Creek is a town in the upper Mersey Valley, in the central north of Tasmania, Australia. Mole Creek is well known for its honey and accounts for about 35 percent of Tasmania's honey production. The locality is in the Meander Valley Coun ...
. The Flowery Gully Limestone near Beaconsfield started deposition at an earlier time Llanvirn or Llandeilo than the limestones further west. In the central north of the Sheffield element is the Early Arenig age Caroline Creek Sandstone on a bed of chert conglomerate. The Cabbage Tree Formation is east of the Andersons Creek Ultramafic Complex, and is sandstone and conglomerate. In North east Tasmania the Mathinna Group starts in the Ordovician with Stony Head Sandstone, a quartz sandstone formed in turbidity flows. Turquoise Bluff Slate formed from shale. Fossils are rare (mostly sparse graptolites), and ages hard to determine.D. B. Seymour and C. R. Calve
''Time – Space Diagram for Tasmania''
Mineral Resources Tasmania and AGSO 1998; an
synthesis
/ref> The Wurawina Supergroup formed in the Duck Creek Syncline amongst other places. This syncline is oriented east–west, located on the west coast south of the mouth of the
Pieman River The Pieman River is a major perennial river located in the West Coast, Tasmania, west coast region of Tasmania, Australia. Course and features Formed by the confluence of the Mackintosh River and Murchison River (Tasmania), Murchison River, the ...
. It consists of conglomerate equivalent to Mount Zeehan Conglomerate, sandstone, siltstone, shale and micrite equivalent to the Gordon Group, and finally equivalents to the Eldon Group (to Devonian). The Wurawina Supergroup also occurs in the Adamsfield Element with the Denison Group consisting of Singing Creek Formation (of quartzawacke), Great Dome Sandstone, Reeds Conglomerate, Squirrel Creek Formation. Then above this the Gordon Group consists of Karmberg Limestone, Cashions Creek Limestone, Benjamin Limestone, and Arndell Sandstone all from shallow marine conditions. Limestones are also found at Lune River, Precipitous Bluff and produced in deeper water at Surprise Bay on the south Coast.


Silurian

The Mathinna Group continued in the
Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleoz ...
period with Bellingham Formation and Sidling Sandstone. In western Tasmania, after the Gordon Group came the Eldon Group consisting of Crotty Quartzite, Amber Slate, Keel Quartzite, Austral Creek Siltstone, Florence Quartzite and Bell Shale. The time of the Eldon group is between
Aeronian In the geologic timescale, the Aeronian is an age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that began 440.8 ± 1.2 Ma and ended 438.5 ± 1.1 Ma (million years ago). The Aeronian Age succeeds ...
and
Pragian The Pragian is one of three faunal stages in the Early Devonian Epoch. It lasted from 410.8 ± 2.8 million years ago to 407.6 ± 2.8 million years ago. It was preceded by the Lochkovian Stage and followed by the Emsian Stage. The most importan ...
, but with a depositional gap in the
Ludlow Ludlow () is a market town in Shropshire, England. The town is significant in the history of the Welsh Marches and in relation to Wales. It is located south of Shrewsbury and north of Hereford, on the A49 road which bypasses the town. The ...
and early Pridoli. In the Adamsfield element is the Tiger Range Group with Gell Quartzite, Richea Siltstone, Currawong Quartzite and possibly McLeod Creek Formation. Upper layers have been removed by erosion.


Devonian

In early to mid
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...
the Tabberabban Orogeny compressed Tasmania in the east–west direction. Reverse faults were activated, and folding with axes running north west and north-north east were formed. Tight folds were formed with axes in the north–south direction at first. Later folding in the northwest to west-northwest direction was superimposed. Faulting relieved some stress and cleavage developed in the rocks. In the Fossey Mountains Trough, the intersecting folds have made
dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...
and basin shaped structures. Uplift and erosion occurred. A quartz-feldspar porphyry intruded the Timbs Group in the southern Arthur Lineament at . In the north east of Tasmania the Mathinna Group received its last deposits in the form of turbidites in the Bellingham Formation and Sidling Sandstone containing more feldspar. Granites were intruded in the east of Tasmania around . The St Marys Porphyrite is an
ash flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of bu ...
of dacite from . Three large
batholith A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, s ...
s are in the north east: Scottsdale, Eddystone and Blue Tier. Gravity measurements show that granite underlies most of north east Tasmania at depth. Its western edge is a shelf running from Noland Bay in the north to Great Oyster Bay on the east coast. Granite also underlies the east coast with outcrops on Freycinet Peninsula, Maria Island, and Tasman Peninsula and the Hyppolite Rocks. The eastern Bass Strait Islands also show large exposures of granite, including Flinders, Cape Barren, and Clarke Island. Even the Tasmanian islands in the far north of Bass Strait are composed of granite, including Rodondo Island, Moncoeur Island, Kent Group including Deal Island, and Judgement Rocks. Hogan Island and Curtis Island. These islands formed a land bridge in the last ice age and butt up against
Wilsons Promontory Wilsons Promontory, is a peninsula that forms the southernmost part of the Australian mainland, located in the state of Victoria. South Point at is the southernmost tip of Wilsons Promontory and hence of mainland Australia. Located at nea ...
in
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...
. In the Blue Tier Granite,
granodiorite Granodiorite () is a coarse-grained ( phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gr ...
came first.
Adamellite Quartz monzonite is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock. The plagiocl ...
intruded, named Mount Pearson Pluton and feeding the St Marys Porphyrite at . A second stage of adamellite came at and alkali-feldspar granite derived by fractional crystallisation followed at . Similar ages and sequences of types apply to the other batholiths. In the batholiths there are quartz-feldspar porphyry and dolerite dykes.
S-type granite S-type granites are a category of granites first proposed in 2001. They are recognized by a specific set of mineralogical, geochemical, textural, and isotopic characteristics. S-type granites are over-saturated in aluminium, with an ASI index gre ...
is only found for sure in the Eddystone Batholith in the most extreme north east. Away from the east the
I-type granite I-type granites are a category of granites originating from igneous sources, first proposed by Chappell and White (1974). They are recognized by a specific set of mineralogical, geochemical, textural, and isotopic characteristics that indicate, fo ...
proportion increases. Veins of gold were crystallised in the Mathinna-Alberton Gold Lineament, a line from Scottsdale to Blue Tier. The
Scamander Scamander (; also Skamandros ( grc, Σκάμανδρος) or Xanthos () was a river god in Greek mythology. Etymology The meaning of this name is uncertain. The second element looks like it is derived from Greek () meaning 'of a man', but t ...
field originated from the edge of the Mount Pearson biotite adamellite-granite pluton, containing
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ...
, tin
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
and
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
veins. Folding and foliation occurred in northeast Tasmania during the Devonian after the granites appeared. The Eldon Group finished forming in a shallow marine environment with quartz sandstone and mudstone lying conformably on the Gordon Group rocks. Fossils include
brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...
s,
gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...
s, bryozoans, and tentaculites.


Granite

In the west of the state there were thirteen small granitic intrusions around . The western plutons were associated with mineralization at Zeehan. The Heemskirk Granite is a D-shaped double intrusion of 120 km2. It has two parts, one part red, and another white granite that intrudes the red, it is high in
tourmaline Tourmaline ( ) is a crystalline Silicate mineral, silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is a gemstone and can be found in a wide variety o ...
. Mineralisation from the Heemskirk Granite with
cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...
or tin and
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
skarn Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate mineral ...
, or silver lead and zinc veins occur in the Zeehan field. The Pieman Granite is a similar age at , but without useful mineral deposits. The Cox Bight granite is white aged at . The South West Cape Granite is dated at . It is foliated and white to cream with
biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more ...
and
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...
in large crystals.P R Williams and E B Corbett,
''Geological Survey Explanatory Report Geological Atlas 1:250,000 series sheet SK55/7 Port Davey''
1977
The Meredith Batholith contains biotite adamellite. It contains ten separate plutons. A
contact aureole Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...
of 2.5 km thickness surrounds the batholith in the form of
albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicate ...
epidote Epidote is a calcium aluminium iron sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in ...
hornfels Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. These pro ...
. The granite formed . Geophysical exploration and a borehole has revealed a large granite mass a kilometer below Zeehan, Renison, Dundas, Rosebery mineral fields. This is the Heemskirk–Granite Tor subsurface ridge. Lamprophyre dykes near Queenstown is . The Grandfathers Granite is an adamellite under 2 km deep south and offshore from Cape Sorell. It has a few isolated outcrops on the surface.
Lamprophyre Lamprophyres () are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica- undersaturated mafic or ultramafic rocks with high magnesium ...
dykes and sheets have intruded at Hibbs Bay and nearby on the south west coast . The Housetop Granite outcrops over 120 km2 at the western end of the Sheffield Element. It is a biotite granite solidified . It produced some mineral veins with lead, silver, zinc, copper and tin-tungsten skarn at Kara. The Dolcoath Granite outcrops near Cethana but extends underground to the west. It has produced
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With ...
fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...
vesuvianite Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism. It was first discovered within ...
mineral deposits at
Moina ''Moina'' is a genus of crustaceans within the family Moinidae. The genus was first described by W. Baird in 1850. They are referred to as water fleas, but are related to the much larger ''Daphnia magna'' and the larger ''Daphnia pulex''. Thi ...
, and tin tungsten
bismuth Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs ...
veins at the Shepherd and Murphy Mine. The Beulah Granite outcrops near Paradise and Beulah and it extends underground to the north and west. Granite Tor Granite as it appears on the surface is just a small part of a large buried granite body that may connect with the Heemskirk Granite. Its age is .


Carboniferous

On the eastern side of King Island some small stocks of granite with dykes intruded. The granites are adamellite-granodiorite with large crystals of
K-feldspar Orthoclase, or orthoclase feldspar (endmember formula K Al Si3 O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles ...
. They are around . They are known as Grassy Granodiorite, and Bold Head Adamellite in the south east, and Sea Elephant Adamellite on the north east is richer in feldspar. Megakinking caused shortening in the NNW-SSE direction in north east Tasmania with blocks up to 9 km across rotated.


Permian

In the Permian, glacial conditions predominated with, icecaps on the land, and ice floating on the sea, as a result of which
tillite image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
is found at the base of the Permian deposits. Mudstone with
dropstone Dropstones are isolated fragments of rock found within finer-grained water-deposited sedimentary rocks or pyroclastic beds. They range in size from small pebbles to boulders. The critical distinguishing feature is that there is evidence that the ...
s was formed in the sea areas, particularly in the eastern half of Tasmania. This eastern zone is known as the Tasmania Basin. The rocks are undeformed and cover the central part of the state, most of the east coast, down to the south coast, and with extensions to the north coast near Launceston and Devonport. What is now visible has been reduced by erosion. The Permian and Triassic deposits together are known as the Parmeener Super Group. The lowest levels are a discontinuous dark grey pebbly tillite up to several hundreds of meters thick. It has been found at Cygnet (Truro Tillite), Glenorchy,
Margate Margate is a seaside town on the north coast of Kent in south-east England. The town is estimated to be 1.5 miles long, north-east of Canterbury and includes Cliftonville, Garlinge, Palm Bay and Westbrook. The town has been a significan ...
, Woodbridge,
Maydena Maydena is a locality in Tasmania, Australia, alongside the River Tyenna. Maydena is on the Gordon River Road, south west of New Norfolk, through the Bushy Park Hop Fields, turn left at Westerway, past Mount Field National Park and Russell Fal ...
, Shoemaker Point and Hastings.
Mount Anne Mount Anne is a mountain located in the Southwest National Park in south-west region of Tasmania, Australia. The mountain lies within the UNESCO World Heritage-listed Tasmanian Wilderness. With an elevation of above sea level, Mount Anne i ...
, Mount Mueller, and
Mount Wedge Mount is often used as part of the name of specific mountains, e.g. Mount Everest. Mount or Mounts may also refer to: Places * Mount, Cornwall, a village in Warleggan parish, England * Mount, Perranzabuloe, a hamlet in Perranzabuloe parish, C ...
are the most south west extension of the tillite. In the north it occurs at Wynyard as the Wynyard Tillite. In the west is the Zeehan Tillite. The broken fragments of rocks are often faceted and scratched, and can be up to boulder sized. They are embedded in rock flour and silt. The ice that brought the till flowed from the west of Tasmania in an easterly direction. The tillite may have started appearing in the Late Carboniferous. Siltstone with
varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (va ...
s is found at Maydena, it is called laminite. Above the tillite is massive mudstone and siltstone with occasional dropstones, the Woody Island Siltstone in southern Tasmania and Quamby Mudstone in the northern half. The upper levels of the marine sequence are siltstone and sandstone with frequent dropstones and fossils. These are the Bundella Formation and Golden Valley Group.
Oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...
forms a layer in the north and at Douglas River in the east. The shale is known as tasmanite. Above this are freshwater deposits of conglomerate, sandstone with pebbles, siltstone with quartz or mica. These freshwater beds can be up to 30m thick. They are called Faulkner Group, the Liffey Group and the Mersey coal Measures. Above this in south east Tasmania are more marine units that include Nassau Formation Berriedale Limestone, up to 60 m thick, siltstone and sandstone rich in fossils and dropstones (Malbina Formation, and Deep Bay Formation), and the upper part is dark grey siltstone rich in dropstones. The very top layers are coloured black, probably from an estuary (Risdon Sandstone and the Abels Bay Formation).
Felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, wh ...
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
is found near the top of the sequence of sediments. Fresh water deposits form the Upper Parmeener Super Group. The layer commence with poorly cemented sandstone, mudstone, carbonaceous mudstone and
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
(Cygnet Coal Measures). ''
Glossopteris ''Glossopteris'' tymology: from Ancient Greek γλῶσσα (glôssa, " tongue ") + πτερίς (pterís, " fern ")is the largest and best-known genus of the extinct Permian order of seed ferns known as Glossopteridales (also known as Arberia ...
'' is frequently found as well as Dulhuntyspora. In the past coal was mined at Mount Cygnet and Adventure BayN Farmer
''Geological Survey Explanatory Report Geological Atlas 1:250,000 series sheet SK55/8 Hobart''
1979
and at Mount Ossa. These sandstones were laid down by east flowing rivers.


Triassic

Continental conditions resulted in sandstone deposits, which represent the upper layers of the Parmeener Super Group. The lowest levels are a sparkling clean quartz sandstone free of coal. The uppermost parts have sandstone and beds of coal. Coal was mined at Newtown, Kaoota, Mount Lloyd,
Strathblane Strathblane ( gd, Strath Bhlàthain, ) is a village and parish in the registration county of Stirlingshire, situated in the southwestern part of the Stirling council area, in central Scotland. It lies at the foothills of the Campsie Fells and th ...
, and on the
Tasman Peninsula The Tasman Peninsula, officially Turrakana / Tasman Peninsula, is a peninsula located in south-east Tasmania, Australia, approximately by the Arthur Highway, south-east of Hobart. The Tasman Peninsula lies south and west of Forestier Peninsula ...
. The sandstone has also been heavily used as building stone. At St Marys there were two
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...
eruptions of alkali-olivine basalt at .
Tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...
from calc-alkaline volcanoes to the east of Tasmania produced some layers in the upper sediments. An ashfall tuff in the Denison Rivulet area of eastern Tasmania is dated at (
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch ...
).


Jurassic

A major intrusion of dolerite occurred in the Jurassic. This was a widespread phenomena covering over one third of Tasmania, and possibly more in the past. This intrusion also affected
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
,
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...
and
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
at . This has been called the
Karoo-Ferrar The Karoo and Ferrar Large Igneous Provinces (LIPs) are two large igneous provinces in Southern Africa and Antarctica respectively, collectively known as the Karoo-Ferrar, Gondwana,E.g. or Southeast African LIP, associated with the initial break- ...
large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...
. Three to five million cubic kilometers of
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
were intruded overall, being the planet's fourth largest known magma intrusion. This may have been the cause of the
Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toar ...
extinction through a consequent oceanic
anoxic event Oceanic anoxic events or anoxic events ( anoxia conditions) describe periods wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and sulfidic) waters. Although anoxic events have not ...
. Henrik Svensen claimed that the magma baked coal and
oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...
producing up to 27.4 teratonnes of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, some of which entered the
Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...
. Tasmania has the largest exposure of dolerite in the world of 30000 km2 and a volume of 15000 km3.D. B. Seymour, G. R. Green and C. R. Calver
The Geology and Mineral Deposits of Tasmania: a summary
Tasmanian Geological Survey Bulletin 72, Mineral Resources Tasmania 2007
In Tasmania the rock is characteristic of many mountains with its columnar joining and dark blue grey colour. The composition is 40%
plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more p ...
, 20%
clinopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe I ...
, 20% quartz, 5%
ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...
and small percentages of potassium feldspar and
amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...
. The rock is altered by water to
smectite A smectite (from ancient Greek ''σμηκτός'' smektos 'lubricated'; ''σμηκτρίς'' smektris 'walker's earth', 'fuller's earth'; rubbing earth; earth that has the property of cleaning) is a mineral mixtures of various swelling sheet sil ...
and
kaolinite Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahed ...
with quartz being left unaltered. The soil surface concentrates
zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
and
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...
. The soils on dolerite also contain nodules of
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
and may contain a buried layer of stones called a stone line.Rafael Osok and Richard Doyle
''Soil development on dolerite and its implications for landscape history in southeastern Tasmania''
Most of the intrusions are in the form of sills up to 500 m thick. Mostly the sills are in the Parmeener Super Group rocks. There are also stepped sills, inclined sheets, cones and some dykes. Closely adjacent country rocks were metamorphosed to
hornfels Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. These pro ...
. The upper parts of sills may be more coarsely grained. Dolerite is crushed to use as road metal, and aggregate. Mount Anne, Mount Mueller, and Mount Wedge in the south west are capped in dolerite, where it also makes contact with Precambrian rocks. It appears that the magma came from the crust rather than the mantle. Solidification occurred at . A Jurassic forest was buried in an andesitic volcanic eruption at Lune River. Here, beneath the lava flow, is mudstone with fossil wood and leaves. On King Island, there was an intrusion of a biotite lamprophyre dyke at .
Xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...
s of
granulite Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associated ...
-facies metamorphic rock resemble those found in eastern Antarctica.


Cretaceous

In the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
continental breakup of
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...
started near Tasmania. About a rift entered the east coast of Tasmania from the south and split off the Lord Howe Rise.
Sea floor spreading Seafloor spreading or Seafloor spread is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. History of study Earlier theories by Alfred Wegener an ...
continued to move this continental sliver away to the east from Tasmania and Australia, and the rift jumped into the Lord Howe Rise and separated off the East Tasman Plateau. This
East Tasman Plateau The East Tasman Plateau is a submerged microcontinent south east of Tasmania. Its area is , and it is mostly from deep. It is a circular piece of continental rocks surrounded by oceanic crust. Volcanism occurred there .C. Gaina, R. D. Müller, ...
microcontinent was originally off the southeast of Tasmania; it is a circular piece of continental rocks surrounded by oceanic crust. Volcanism occurred there . In the Cretaceous Bass Strait was stretched and thinned and became filled with water. Vulcanism occurred in the Bass Basin. Flowering plants moved into Tasmania about . At these times Tasmania was still connected to Antarctica with the southwest abutting
Oates Land Oates Land is a region of Antarctica. It is variously defined as a portion of the East Antarctica near the coast stretching along and inland from the Oates Coast (see map) and as an officially delineated wedge-shaped segment of the Australian ...
and the Wilson Hills. South from Tasmania is an extension of continental crust called the South Tasman Rise. The Gilbert Seamount was split from the South Tasman Rise by sea floor spreading about .C. Gaina, R. D. Müller, B. Brown and T. Ishihara
''Microcontinent formation around Australia''
in Geological Society of Australia Special Publication 22, 2001 page 400-405
This extension created a number of sedimentary basins:
Bass Bass or Basses may refer to: Fish * Bass (fish), various saltwater and freshwater species Music * Bass (sound), describing low-frequency sound or one of several instruments in the bass range: ** Bass (instrument), including: ** Acoustic bass gui ...
, Durroon,
Gippsland Gippsland is a rural region that makes up the southeastern part of Victoria, Australia, mostly comprising the coastal plains to the rainward (southern) side of the Victorian Alps (the southernmost section of the Great Dividing Range). It cove ...
, Otway and Sorell Basins. They each contain several kilometres of sediment from the late Mesozoic to Cenozoic time periods. Bass Basin, between King Island, and north from the
Tamar River The Tamar River, officially kanamaluka / River Tamar, is a estuary located in northern Tasmania, Australia. Despite being called a river, the waterway is a brackish and tidal estuary over its entire length. Location and features Formed by the ...
, has up to 12 km of sediment, actually starting from the Jurassic. The lowest layer is the Otway Group of sandstone made from rock fragments. The Eastern View Coal Measures follow. The Latrobe Group found in the Otway Basin, closer to Victoria, is from the same time and produces the oil found in the area. From Late Paleocene to early Eocene there was an unconformity. A shale from Demons Bluff Formation follows in the Eocene, deposited in calm sea water. The Torquay Group reaches from Oligocene to the current day, with
marl Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part ...
and limestone formed in open sea water. The Durroon Basin is south east of the Bass Basin. Late Cretaceous rocks are conglomerate, with sandstones above. From there was a high thermal gradient of 55° per km. Around there was uplift and erosion of 900 m of sediment called Southern Ocean breakup unconformity. A layer of olivine basalt lies on this, followed by carbonaceous shale for 300 m called Durroon Mudstone . This was deposited in a lake. Non marine sediment follow from Cretaceous, through Paleocene to Eocene . From the Demons Bluff Formation sandstone formed, and finally the Torquay Group with more sandstone and shale than in the Bass Basin. Rocks from the Cretaceous include
syenite Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). Some syenites contain larger prop ...
porphyry sills and dykes near Cygnet around . They intrude the Lower Parmeener Group rocks, and dolerite. There are two kinds of composition, one is high alkali, alumina, silicon and barium containing melanite
garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different ...
; the other is high in potassium with
nepheline Nepheline, also called nephelite (), is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate, Na3 K Al4 Si4 O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmati ...
and hauyne. This rock is
banatite Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...
. Clay from this was mined at Police point, and there are also some gold deposits. There is likely to be a giant
laccolith A laccolith is a body of intrusive rock with a dome-shaped upper surface and a level base, fed by a conduit from below. A laccolith forms when magma (molten rock) rising through the Earth's crust begins to spread out horizontally, prying apar ...
of syenite below Cygnet. Cape Portland is host to andesite, lamprophyre and porphyrite intrusions and eruptions from . Musselroe Bay nearby has a lamprophyre and basalt from .


Cenozoic


Pre-Quaternary


=Tectonics

= Tasmania finally disconnected from Antarctica . Several basins were formed by faulting. Faulting was connected with continental breakup. Most faulting was finished by the
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...
, but the Sorell Basin continued into the
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...
. Cenozoic age deposits are found in the northern midlands (Tamar Graben), and south of
Macquarie Harbour Macquarie Harbour is a shallow fjord in the West Coast region of Tasmania, Australia. It is approximately , and has an average depth of , with deeper places up to . It is navigable by shallow-draft vessels. The main channel is kept clear by th ...
in the Macquarie Harbour Graben. In the south east are the Derwent Graben and the Coal River Graben. Thick layers of Cenozoic rocks are found in the estuary of the Derwent River,
D'Entrecasteaux Channel The D'Entrecasteaux Channel is a body of water located between Bruny Island and the south-east of the mainland of Tasmania, Australia. The channel is the mouth for the estuaries of the Derwent and the Huon Rivers and empties into the Tasman S ...
, Sandy Bay,
Taroona Taroona is a major residential suburb approximately 15 minutes drive from the centre of Hobart, Tasmania on the scenic route between Hobart and Kingston. Although on the edges of the City of Hobart, Taroona is actually part of the municipality ...
, Middleton, Craigow Hill, and Spring Bay. The rocks are mostly siltstone and clay. The deep estuary rocks are from the
Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pala ...
.
Travertine Travertine ( ) is a form of terrestrial limestone deposited around mineral springs, especially hot springs. It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by a p ...
is found at Geilston Bay.
Silcrete Silcrete is an indurated (resists crumbling or powdering) soil duricrust formed when surface soil, sand, and gravel are cemented by dissolved silica. The formation of silcrete is similar to that of calcrete, formed by calcium carbonate, and ferr ...
and
laterite Laterite is both a soil and a rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by ...
from this time is found too. The Macquarie Harbour
graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic conte ...
deposits dating from Palaeocene and Eocene are poorly consolidated sand, and gravel, with some beds of
lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
and clay. Sediments are up to 500 meters thick, with the lowest layers consisting of dolerite boulders. The Tamar Graben was an extension to the south of the Bass Basin onto the Tasmanian island. Sediments started in the graben at the very end of the Cretaceous, and into the Paleocene and Eocene with conglomerate, sandstone, mudstone and lignite. Basalt and conglomerate is buried south of White Hills. There is Eocene carbonaceous silt. The Longford Sub-basin extends inland south of the Tamar Graben, and is filled with 800 m of clay, sand and gravel, with some basalt towards the top layers, mostly from the Eocene. The Devonport-Port Sorell Sub-Basin was formed in Paleocene with carbonaceous mudstone and sandstone. The Thirlstane Basalt is above at , an alkali-olivine basalt. Then the Wesley Vale Sand follows, and the Moriarty Basalt is 50 meters thick at . The Sorell Basin forms the
continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
off the west coast. It has sub-basins of King Island, Sandy Cape, Strahan, and Port Davey which were formed in the Early Cretaceous. The King Island Basin is terminated on the east by a normal fault. It is south of King Island and north west of Tasmania. It has a basement of the Rocky Cape Group from the Proterozoic. The first sediments are red conglomerate beds for 190 m. mid-Upper Cretaceous sandstone and mudstone follow, the same age as the Sherbrook Group. Then more conglomerate sandstone and mudstone matching the Wangerrip Group up to early Eocene. Quartz sandstone is above this, with marl, mudstone and limestone from Oligocene and
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
age. There is an
unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
at the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Flinders Island Flinders Island, the largest island in the Furneaux Group, is a island in the Bass Strait, northeast of the island of Tasmania. Flinders Island was the place where the last remnants of aboriginal Tasmanian population were exiled by the colo ...
just above sea level. The Scottsdale sub-basin is up to 225 meters thick from the late Oligocene to early Miocene.


=Basalt

= Volcanic vents opened up . Lava flows of basalt up to 20 meters thick were formed. Some volcanoes were explosive with
bombs A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanic ...
, and
pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...
. The eruptions are probably from the Oligocene and Miocene. The earliest eruption was at
Bream Creek Bream Creek is a rural locality in the local government area (LGA) of Sorell in the South-east LGA region of Tasmania. The locality is about east of the town of Sorell. The 2016 census has a population of 124 for the state suburb of Bream Cree ...
on the east coast at . From Weldborough it is but mostly eroded. In the south east, basalt from Sandy Bay dates from .
Campania (man), it, Campana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = , demographics1_footnotes = , demographics1_title1 = , demographics1_info1 = , demog ...
has an alkali basalt from but it also has younger flows of olivine tholeiites. From near Hobart there is olivine basalt from . In north east Tasmania, there are many lava flows from middle Eocene to early Miocene. There are at least four types: alkali olivine basalt, quartz tholeiite , alkaline basalt, and olivine
nephelinite Nephelinite is a fine-grained or aphanitic igneous rock made up almost entirely of nepheline and clinopyroxene (variety augite). If olivine is present, the rock may be classified as an olivine nephelinite. Nephelinite is dark in color and may res ...
. Lava flows in the north east flowed down valleys to the sea. In the north west, there was so much lava that valleys filled and overflowed. A plain resulted with up to 750 meters thickness, and maximum extent south of Wynyard and Burnie. In the late Eocene and early Oligocene lakes were formed near
Waratah Waratah (''Telopea'') is an Australian-endemic genus of five species of large shrubs or small trees, native to the southeastern parts of Australia (New South Wales, Victoria, and Tasmania). The best-known species in this genus is ''Telopea speci ...
. Older alkaline basalt in the north west is from , at Table Cape
basanite Basanite () is an igneous, volcanic ( extrusive) rock with aphanitic to porphyritic texture. It is composed mostly of feldspathoids, pyroxenes, olivine, and plagioclase and forms from magma low in silica and enriched in alkali metal oxides tha ...
from and at Stanley basanite is dated to and . Mount Cameron West has olivine basalt from 15.5 and 14.4 Ma. On the southern part of the Central Plateau, there are olivine
melilite Melilite refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite and åkermanite. A generalized formula for common melilite is ( Ca, Na)2( Al, Mg, ...
nephelinite, olivine nephelinite, quartz tholeiite lava flows. These ran south down tributaries of the Derwent River . On the east side of the Central Plateau an olivine nephelinite is from , and a flow of nepheline
hawaiite Hawaiite is an olivine basalt with a composition between alkali basalt and mugearite. It was first used as a name for some lavas found on the island of Hawaii. It occurs during the later stages of volcanic activity on oceanic islands such as Ha ...
is from . In the western Midlands there is basalt from , and hawaiites from 25 and . Around Launceston, igneous rocks were intruded into Cenozoic sediments forming dolerite and monzonite.


Quaternary

In the
Ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...
there were valley glaciers and a 1000 km2
ice cap In glaciology, an ice cap is a mass of ice that covers less than of land area (usually covering a highland area). Larger ice masses covering more than are termed ice sheets. Description Ice caps are not constrained by topographical feat ...
. Glaciation on Mount Field occurred 41-44 ka during MIS 3, and 18 ka during MIS 2 with ice free conditions at 16 ka. A. N. Mackintosh, T. T. Barrows E. A. Colhoun and L. K. Fifield
''Exposure dating and glacial reconstruction at Mount Field, Tasmania, Australia, identifies MIS 3 and MIS 2 glacial advances and climatic variability''
in ''Journal of Quaternary Science'' Vol. 21(4) p363-376 2006.
The ice cap on the Central Plateau was around 65 km in diameter. Its western limit was the
Du Cane Range The Du Cane Range is a mountain range in the Central Highlands region of Tasmania, Australia. An unnamed peak on the main ridge of the Du Cane Range has an elevation of above sea level and is the eleventh highest mountain peak in Tasmania. ...
and
Lake St Clair Lake St. Clair (french: Lac Sainte-Claire) is a freshwater lake that lies between the Canadian province of Ontario and the U.S. state of Michigan. It was named in 1679 by French Catholic explorers after Saint Clare of Assisi, on whose feast day ...
. The central part under the ice cap was eroded. Significant areas of till are found in the central highlands arranged roughly in a circle around the former ice cap. Glaciers flowed out into the
Franklin River The Franklin River is a major perennial river located in the Central Highlands and western regions of Tasmania, Australia. The river is located in the Franklin-Gordon Wild Rivers National Park at the mid northern area of the Tasmanian Wilder ...
, the Canning Valley, and north into
Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotla ...
and
Mersey The River Mersey () is in North West England. Its name derives from Old English and means "boundary river", possibly referring to its having been a border between the ancient kingdoms of Mercia and Northumbria. For centuries it has formed part ...
Rivers. Glaciers were in a number of locations on the west coast – at Mount Murchison,
Mount Tyndall Mount Tyndall is a peak in the Mount Whitney region of the Sierra Nevada in the U.S. state of California. At , it is the tenth highest peak in the state. The mountain was named in honor of the Irish scientist and mountaineer, John Tyndall. G ...
and the
Eldon Range The Eldon Range is a mountain range located in the West Coast, Tasmania, west coast region of Tasmania, Australia. The range is located at the north eastern edge of Lake Burbury and is part of the Tasmanian Wilderness World Heritage Area which ...
. Glaciers flowed into the
Henty River The Henty River is a perennial river in the West Coast region of Tasmania, Australia. The river generally lies north of and south of . Location and features Formed by the confluence of the Dobson and Newton Creeks, the river rises below Lake ...
and King River. Moraines were deposited at Crotty and the Henty Road. Ice pushed out from the King River Glacier into
Linda Linda may refer to: As a name * Linda (given name), a female given name (including a list of people and fictional characters so named) * Linda (singer) (born 1977), stage name of Svetlana Geiman, a Russian singer * Anita Linda (born Alice Lake i ...
, Comstock and Nelson Valleys. Wood from the Linda moraine had a
carbon-14 Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and co ...
age of 26480 years. There are also
cirque A (; from the Latin word ') is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic , meaning a pot or cauldron) and (; ). A cirque may also be a similarly shaped landf ...
s on Frenchmans Cap, the
West Coast Range The West Coast Range is a mountain range located in the West Coast region of Tasmania, Australia. The range lies to the west and north of the main parts of the Franklin-Gordon Wild Rivers National Park. The range has had a significant nu ...
, the Denison Range, and King William Range.K. D. Corbett, A. V. Brown
''Geological Survey Explanatory Report Geological Atlas 1:250,000 series sheet SK55/5 Queenstown''
1976
Several
cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
s have developed in dolomite and limestone. Well known are King Solomons Cave and Marakoopa Cave at
Mole Creek Mole Creek is a town in the upper Mersey Valley, in the central north of Tasmania, Australia. Mole Creek is well known for its honey and accounts for about 35 percent of Tasmania's honey production. The locality is in the Meander Valley Coun ...
, and the Newdgate Cave at
Hastings Hastings () is a large seaside town and borough in East Sussex on the south coast of England, east to the county town of Lewes and south east of London. The town gives its name to the Battle of Hastings, which took place to the north-west ...
. Periglacial activity broke up rocks with
ice wedge An ice wedge is a crack in the ground formed by a narrow or thin piece of ice that measures up to 3–4 meters in length at ground level and extends downwards into the ground up to several meters. During the winter months, the water in the gr ...
s and formed block fields and block streams. Gravels are also left from rivers in Quaternary times. These include the
Huon River The Huon River is a perennial river located in the south-west and south-east regions of Tasmania, Australia. At in length, the Huon River is the fifth-longest in the state, with its course flowing east through the fertile Huon Valley and empt ...
with gravel at Randals Bay, Judbury and Beaupre Point. The pebbles are mostly quartzite, but include dolerite and
agate Agate () is a common rock formation, consisting of chalcedony and quartz as its primary components, with a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate was common in Ancie ...
.


South Tasman Rise

A ridge of continental crust extends south of Tasmania below sea level. It contains quartz syenite from , and Cenozoic volcanics.


Macquarie Island

Macquarie Island Macquarie Island is an island in the southwestern Pacific Ocean, about halfway between New Zealand and Antarctica. Regionally part of Oceania and politically a part of Tasmania, Australia, since 1900, it became a Tasmanian State Reserve in 197 ...
is politically part of the state of Tasmania, but comes from a very different geological context. It has formed as part of the
oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumu ...
and mantle was buckled upwards. It is the only place in the world where a complete section of oceanic crust is exposed above water in the place it was formed. The rock composing the island was formed at the
ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...
along the boundary of the
Australian Plate The Australian Plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately when India broke ...
and the
Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...
in
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...
times . Spreading from the ridge became less perpendicular (ESE-WNW), more oblique (SE-NW) and eventually almost parallel to the ridge (NNE-SSW). The
plate boundary Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
is now entirely a
transform fault A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...
a few kilometers to the west of the island. This left fracture zones and spreading fabric in the rock. The
geomagnetic reversals A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's field has alternated b ...
leave a
magnetic anomaly In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...
trace in the rock. Transpression on the plate boundary has deformed the oceanic crust in the vicinity to make the Macquarie Ridge Complex, raising Macquarie Island out of the water. It is studied to understand
seafloor spreading Seafloor spreading or Seafloor spread is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. History of study Earlier theories by Alfred Wegener an ...
and transform faults, and
hydrothermal alteration Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical com ...
of the undersea floor. Most of the south of the island consists of sub oceanic basalt layered between
Globigerina ''Globigerina'' () is a genus of planktonic Foraminifera, in the order of Rotaliida.Glo ...
ooze. The part north of Langdon Point and Ballast Bay consists of
serpentinite Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''s ...
derived from gabbro,
troctolite Troctolite (from Greek τρώκτης 'trout' and λίθος 'stone') is a mafic intrusive rock type. It consists essentially of major but variable amounts of olivine and calcic plagioclase along with minor pyroxene. It is an olivine-rich anorth ...
, and
peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high pr ...
(
dunite Dunite (), also known as olivinite (not to be confused with the mineral olivenite), is an intrusive igneous rock of ultramafic composition and with phaneritic (coarse-grained) texture. The mineral assemblage is greater than 90% olivine, w ...
, wehrlite, and
harzburgite Harzburgite, an ultramafic, igneous rock, is a variety of peridotite consisting mostly of the two minerals olivine and low-calcium (Ca) pyroxene (enstatite); it is named for occurrences in the Harz Mountains of Germany. It commonly contains a f ...
). This was formed in the deep crust and mantle. The two different rock zones are separated by the Finch-Langdon fault zone. It consists of seven segments of faults, subsidiary faults and splays. The fault is a transform fault with a corner at the
spreading ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...
. South of the fault on the west coast is breccia interbedded with the basalts. The breccia matrix is mud, and the stones consist of basalt, dolerite, and gabbro. The southern end of Bauer Bay has a talus of breccia 140 m thick. On top is
greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...
and
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...
. Many other faults cut the rock due to stress from the transform, and uplift. Some of these have scarps that dam lakes.Karah L. Wertz et al.:''Macquarie Island's Finch-Langdon fault: A ridge-transform inside corner structure'' in ''Frontier Research on Earth Evolution'', volume 1


Plate tectonics

Various theories describe the past history of Tasmania in relation to other continental masses. Most models have the south west Tasmania abutting East Antarctica. In the missing link model, Z. X. Li has south west China positioned off the east coast of Tasmania with rifting at , with the Kamding dykes in China matching some granites from Tasmania. Tasmania can be subdivided into two terranes, separated by the Tamar Fracture System, on a line from the Tamar River to Sorell in the south east. The West Tasmania Terrane constitutes most of the state, including all the Precambrian and Cambrian rocks. The East Tasmania Terrane makes up the north east and east coasts dating from the Ordovician. In the model of Moore Betts and Hall, Precambrian Tasmania was part of a microcontinent called VanDieland. VanDieland was first proposed by Cayley in 2011. It consists of Western Tasmania, the South Tasman Rise, the
East Tasman Plateau The East Tasman Plateau is a submerged microcontinent south east of Tasmania. Its area is , and it is mostly from deep. It is a circular piece of continental rocks surrounded by oceanic crust. Volcanism occurred there .C. Gaina, R. D. Müller, ...
and the Selwyn block in the central
Lachlan Orogen The Lachlan Fold Belt (LFB) or Lachlan Orogen is a geological subdivision of the east part of Australia. It is a zone of folded and faulted rocks of similar age. It dominates New South Wales and Victoria, also extending into Tasmania, the Austra ...
. In the time of the
Rodinia Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago and broke up 750–633 million years ago. were probably ...
supercontinent, southern VanDieland was next to southwestern Laurentia, part of the Grenville Front. Central VanDieland was next to the Miller Range in the Transantarctic Mountains in East Antarctica. VanDieland separated during the late Neoproterozoic moving north to the Robertson Bay Terrane in
North Victoria Land North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north'' is ...
. The different elements making up Precambrian assembled together from microcontinental ribbon terranes (also termed crustal megaboudins). These elements or ribbons collided on the western edge, or on the northeastern edge of the VanDieland microcontinent causing it to grow. In this period, into the Cambrian, a subduction zone absorbed the convergence of the proto-Pacific plate beneath the microcontinent. The Tasmanian terranes only accreted onto
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...
in the
Middle Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
in the Tabberabberan Orogeny. The westernmost microcontinental ribbon terrane is the King Island element. This not only consists of King Island, but also a strip extending all the way just off shore from the west coast of Tasmania, and north to Phillip Island under Bass Strait. The Barrow River Fault is a major Paleozoic fault. In the section from the west of King Island it has a north-northwest orientation and had a sinistral displacement of 70 km. Just to the north of the western end of
Macquarie Harbour Macquarie Harbour is a shallow fjord in the West Coast region of Tasmania, Australia. It is approximately , and has an average depth of , with deeper places up to . It is navigable by shallow-draft vessels. The main channel is kept clear by th ...
the fault changes direction and heads south. But the southern section only has 5 km of displacement. The Rocky Cape Block which is mainly in the far northwest Tasmania also includes parts that have been shifted south by the Barrow River Fault. The Sorell Peninsula south of Macquarie Harbour, and the tip of Point Hibbs are also part of this element. The Eastern boundary of the Rocky Cape Block is marked by the Arthur Metamorphic complex in the north, and a fault in the south. These structures dip to the east 30°, and have had sinistral movement at 516 Ma. East of this block is the Burnie Zone. The Pedder Zone lies east, and makes up south and south west Tasmania. The Tyennan Zone is separated from the Pedder Zone by eastward dipping Mt Hobhouse Fault.


Geohazards

The east side of the island of Tasmania is in a low earthquake area. The western highlands is part of a belt of seismic activity that includes highlands in eastern Victoria and New South Wales. Just off the north east coast is a point with a large number of tremors, believed to be an incipient volcano. Macquarie Island is in an earthquake region. On 23 December 2004 an earthquake measuring 8.1 on the
Richter magnitude scale The Richter scale —also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale—is a measure of the strength of earthquakes, developed by Charles Francis Richter and presented in his landmark 1935 ...
(one of the largest earthquakes ever recorded) rocked the island, but caused little damage. The last major earthquake in Tasmania was between magnitude 6.5 and 7 at the Lake Edgar Fault in the Recent Period, but more than 200 years ago. On 4 June 1872, a large landslip collapsed part of the side of Mount Arthur. A huge debris flow descended Humphrys Rivulet, stripping the upstream parts of trees and regolith. Where Glenorchy is now, a flood 600 meters wide engulfed farms. Broken trees, boulders, and mud were deposited. Remarkably no one lost their life as all escaped to safety when hearing the rumbling in the distance.


Minerals

Several unusual minerals are known from Tasmania:
crocoite Crocoite is a mineral consisting of lead chromate, Pb Cr O4, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment. Description Crocoite is commo ...
,
stichtite Stichtite is a mineral, a carbonate of chromium and magnesium; formula Mg6 Cr2 C O3(O H)16·4 H2O. Its colour ranges from pink through lilac to a rich purple colour. It is formed as an alteration product of chromite containing serpentine. I ...
, ferroaxinite from Dundas,
sellaite Sellaite is a magnesium fluoride mineral with the formula MgF2. It crystallizes in the tetragonal crystal system, typically as clear to white vitreous prisms. It may be fibrous and occur as radiating aggregates. It has a Mohs hardness of 5 to 6 ...
,
chondrodite Chondrodite is a nesosilicate mineral with formula . Although it is a fairly rare mineral, it is the most frequently encountered member of the humite group of minerals. It is formed in hydrothermal deposits from locally metamorphosed dolomite. I ...
,
norbergite Norbergite is a nesosilicate mineral with formula Mg3( Si O4)( F, OH)2. It is a member of the humite group. It was first described in 1926 for an occurrence in the Östanmoss iron mine in Norberg, Västmanland, Sweden, for which it is named. ...
,
wagnerite Wagnerite is a mineral, a combined phosphate and fluoride of iron and magnesium, with the formula . It occurs in pegmatite associated with other phosphate minerals. It is named after Franz Michael von Wagner (1768–1851), a German mining offic ...
and
fluoborite Fluoborite has a chemical formula of Mg3(BO3)(F,OH)3. Its name comes from its main chemical components, FLUOrine and BORon. It was first described in 1926. Fluoborite's crystal system is hexagonal, meaning it has one six-fold axis of rotation. It ...
from Mount Bischoff,
heazlewoodite Heazlewoodite, Ni3S2, is a rare sulfur-poor nickel sulfide mineral found in serpentinitized dunite. It occurs as disseminations and masses of opaque, metallic light bronze to brassy yellow grains which crystallize in the trigonal crystal system. ...
(Originally discovered in Tasmania) and
shandite Shandite is a sulfide mineral with chemical formula: Ni3Pb2S2. It was discovered in 1948 by the German mineralogist Paul Raumdohr who named it named after Scottish petrologist, Samuel James Shand (1882–1957). Ramdohr characterized shandite ...
from the Trial Harbour nickel mine. From Mount Lyell there are rare minerals:
mawsonite Mawsonite is a brownish orange sulfosalt mineral, containing copper, iron, tin, and sulfur: Cu6Fe2SnS8. Discovery and occurrence It was first described in 1965 for occurrences in the Royal George mine, Swinton, Tingha, Hardinge County, New So ...
, betechtinite, florenceite,
hessite Hessite is a mineral form of disilver telluride (Ag2Te). It is a soft, dark grey telluride mineral which forms monoclinic crystals. It is named after Germain Henri Hess (1802–1850). Hessite is found in the US in Eagle County, Colorado and in ...
,
jalpaite Jalpaite is a rare copper silver sulfide mineral with formula Ag3CuS2. It was first described in 1858 for an occurrence in the Leonora Mine, Jalpa, Zacatecas, Mexico and named for the locality. It occurs in low temperature hydrothermal veins at t ...
, magnesiofoitite,
svanbergite Svanbergite is a colorless, yellow or reddish mineral with the chemical formula Sr Al3( P O4)( SO4)(O H)6. It has rhombohedral crystals.Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig: " Dana's new ...
woodhousite,
stannoidite Stannoidite is a sulfide mineral composed of five chemical elements: copper, iron, zinc, tin and sulfur. Its name originates from Latin ''stannum'' (tin) and Greek ''eides'' (or Latin ''oïda'' meaning "like"). The mineral is found in hydrothermal ...
, stromeyerite, and
zunyite Zunyite is a sorosilicate mineral, Al13 Si5 O20(O H, F)18 Cl, composed of aluminium, silicon, hydrogen, chlorine, oxygen, and fluorine. Occurrence Zunyite occurs in highly aluminous shales and hydrothermally altered volcanic rocks. It occurs ...
.
Tasmanite Tasmanite is a sedimentary rock type almost entirely consisting of the prasinophyte alga ''Tasmanites''. It is commonly associated with high-latitude, nutrient-rich, marginal marine settings find in Tasmania. It is classified as marine type oil ...
the mineral named after Tasmania is in Dana's classification as an Oxygenated hydrocarbon. It consists of reddish brown scales about 1 mm across. It is insoluble in
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
,
carbon disulfide Carbon disulfide (also spelled as carbon disulphide) is a neurotoxic, colorless, volatile liquid with the formula and structure . The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non ...
,
turpentine Turpentine (which is also called spirit of turpentine, oil of turpentine, terebenthene, terebinthine and (colloquially) turps) is a fluid obtained by the distillation of resin harvested from living trees, mainly pines. Mainly used as a special ...
, ether or alcohol. It contains about 5% sulfur. It is found on the banks of the Mersey River. The shale it is present in, is a kind of
oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...
. Pelionite is a name for cannel coal from
Mount Pelion East Mount Pelion East is a mountain located in the Central Highlands region of Tasmania, Australia. The mountain is situated within the Cradle Mountain-Lake St Clair National Park. With an elevation of above sea level, the mountain is the 25 h ...
and
Barn Bluff Barn Bluff is a mountain located in the Central Highlands region of Tasmania, Australia. The mountain is situated in the Cradle Mountain-Lake St Clair National Park at the junction of the easternmost points of the Murchison and Mackintosh ...
. This term is no longer used.
William Frederick Petterd William Frederick Petterd was a Tasmanian scientist and boot importer. He was born in Hobart in 1849, and died in Launceston in 1910. His first book, ''A Monograph of the land shells of Tasmania'', was the result of a talk to the Royal Society ...
was an amateur who studied minerals in Tasmania. He built up the Petterd collection which was donated to the
Royal Society of Tasmania The Royal Society of Tasmania (RST) was formed in 1843. It was the first Royal Society outside the United Kingdom, and its mission is the advancement of knowledge. The work of the Royal Society of Tasmania includes: * Promoting Tasmanian historic ...
and stored at the
Tasmanian Museum and Art Gallery The Tasmanian Museum and Art Gallery (TMAG) is a museum located in Hobart, Tasmania. The museum was established in 1846, by the Royal Society of Tasmania, the oldest Royal Society outside England. The TMAG receives 400,000 visitors annually. ...
. He discovered
dundasite Dundasite is a rare lead aluminium carbonate mineral. The mineral is named after the type locality, Dundas, Tasmania, Australia. The mineral was first discovered in the Adelaide Proprietary Mine. Dundasite was first described by William Frederick ...
, named from the mine where it was found. Dundaisite has formula PbAl2(CO3)2(OH)4.H2O. It is a silky milk white spherical aggregate. Philipsbornite, PbAl3(AsO4)2(OH)5.H2O was originally found in the Adelaide mine and identified as a new mineral by Professor Kurt Walenta. It was named after another German professor Helmuth Richard Hermann Adolf Friedrich von Philipsborn. It occurs as several other mines and appears as a greenish grey earth.
Shandite Shandite is a sulfide mineral with chemical formula: Ni3Pb2S2. It was discovered in 1948 by the German mineralogist Paul Raumdohr who named it named after Scottish petrologist, Samuel James Shand (1882–1957). Ramdohr characterized shandite ...
, Ni3Pb2S2, was first discovered at Trial Harbour by P. Ramdohr in 1960.


Geophysics

The
geothermal gradient Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth's interior. As a general rule, the crust temperature rises with depth due to the heat flow from the much hotter mantle; away from tectonic plate bo ...
was measured at a gas seep in Smithton as 26.4 degrees/km. The gradient at
Forest, Tasmania Forest is a locality and small rural community in the local government area of Circular Head, in the North West region of Tasmania. It is located about east of the town of Smithton. The Bass Highway follows the north-western boundary from nor ...
is 27.8 °C/km. The
Otway Basin The Otway Basin is a northwest trending sedimentary basin located along the southern coast of Australia. The basin covers an area of 150,000 square kilometers and spans from southeastern South Australia to southwestern Victoria, with 80% lying off ...
has a gradient of 36 °C/km. Several companies are exploring for hot rocks for
geothermal energy Geothermal energy is the thermal energy in the Earth's crust which originates from the formation of the planet and from radioactive decay of materials in currently uncertain but possibly roughly equal proportions. The high temperature and pres ...
. The granite areas have a gradient of 30°/km, whereas the Parmeener sedimentary areas have a gradient of 40°/km. Heat flow is between 85 and 159 mW/m2. Active seismic exploration reveals the nature of the deep crust. It shows that the Tyennan block plumbs the depth to the moho which is about 33 km underneath. The Tyennan Block slopes below the Adamsfield-Jubilee Element. Under the Tasmania Basin the block is stretched, with faults in to several large blocks that have tilted down. Above these the Adamsfield-Jubilee Element sediments have filled in the topography. Below the north east element the moho is 36 km deep with alternating seismically fast and slow rocks in the mid crust. The Tyennan Block and the Rocky Cape Element have a boundary that dips at 30° to the east to the base of the crust. The Dundas Element lies on top of this boundary. A shallower Moho occurs under the Rocky Cape Block at 26 to 28 km. A deep segment is found under the central north of the state, down to 34 km. Shallower moho depths also occur under southeast and southern Tasmania. A low seismic velocity zone occurs under the Tamar Fracture System. East of this zone is the Northeast Tasmania Block with higher seismic velocities. The high speed zone boundary meets the east coast near
Little Swanport, Tasmania Little Swanport is a rural locality and an estuary in the local government area of Glamorgan–Spring Bay in the South-east region of Tasmania. It is especially significant for the Little Swanport language. The locality is about north of the ...
but the high speed zone also includes Maria Island and Forestier Peninsula. the Bass Strait is a low seismic velocity zone. Magnetic field measurements show that the different elements making up Tasmania have very different signatures. Wherever there is Jurassic Dolerite, the magnetic map shows fine ripples, so the Tasmania Basin stands out, as does the smaller intrusions in the other elements. The North east element is smooth, as is the Tyennan Block, and the Adamsfield-Jubilee Element. The Dundas Element has a smooth background with prominent north–south ridges. The Rocky Cape Element is densely packed with linear textures parallel to the Arthur Lineament, with the Smithton Syncline showing as a Y shape. King Island also shows north–south texture. Basalt south of Wynyard also shows a wrinkly magnetic signature. The stress field in the crust has not yet been measured.


Mining

World class mineral deposits of base and precious metals were found in western Tasmania. Major mines are at Mount Lyell, Rosebery,
Zeehan Zeehan is a town on the west coast of Tasmania, Australia south-west of Burnie. It is part of the West Coast Council, along with the seaport Strahan, and neighbouring mining towns of Dundas, Rosebery and Queenstown. History The greater ...
, Que River,
Henty Henty may refer to: Australian geography *Henty, New South Wales * Henty, Victoria * Henty (wine) an Australian geographical indicator and wine region in southwestern Victoria *Division of Henty, a former federal electorate in Victoria *Henty Highw ...
and Savage River. Many are hosted in the Mount Read Volcanics. They are in the form of massive sulfides. The Mount Lyell mine extracts copper and gold. The Renison Bell mine was the largest primary tin producer in Australia. Mount Lyell gold and copper deposit was discovered in 1883, formerly the biggest copper mine, and operating till this day. The Savage River ore body is in the Bowry Formation in the Arthur Metamorphic Complex. It consists of
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With ...
,
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
,
chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mo ...
and tiny amounts of
sphalerite Sphalerite (sometimes spelled sphaelerite) is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimen ...
,
ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...
and
rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer Polymorphism (materials science), polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest ...
. The ore was formed under the sea in association with volcanism. The Savage River area also contains deposits of
magnesite Magnesite is a mineral with the chemical formula (magnesium carbonate). Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts. Occurrence Magnesite occurs as veins in and an alteration product of ultramafic ro ...
in the form of marble. At
Beaconsfield Beaconsfield ( ) is a market town and civil parish within the unitary authority of Buckinghamshire, England, west-northwest of central London and south-southeast of Aylesbury. Three other towns are within : Gerrards Cross, Amersham and High W ...
, 1.95 million ounces of
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
was mined from a quartz reef in a fault. The largest Tasmanian
gold nugget :''"Gold nugget" may also refer to the catfish Baryancistrus xanthellus or the mango cultivar Gold Nugget.'' A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate nuggets and finer gold in placers. Nuggets a ...
was found at Rocky River in 1883, weighing 243 ounces. An oil exploration boom happened in the 1920s with two companies making bold claims, but earning nothing from
oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...
.
Asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...
was mined from the Cape Sorell and Serpentine Hill ultramafic complexes.


History

Abel Janszoon Tasman Abel Janszoon Tasman (; 160310 October 1659) was a Dutch seafarer, explorer, and merchant, best known for his voyages of 1642 and 1644 in the service of the Dutch East India Company (VOC). He was the first known European explorer to reach New Z ...
noted in his journal on 22 November 1642 that his compasses were not steady and deduced the presence of deposits of
lodestone Lodestones are naturally magnetized pieces of the mineral magnetite. They are naturally occurring magnets, which can attract iron. The property of magnetism was first discovered in antiquity through lodestones. Pieces of lodestone, suspen ...
. This was two days before his lookout spotted Tasmania for the first time. This was the first prognostication of mineral wealth on the west coast of Tasmania. A. W. Humphrey, a mineralogist, collected rocks and minerals from 1804. W. H. Twelvetrees and W. F. Petterd did petrographic investigations in Cygnet, around 1899.R. S. Bottrill
''A mineralogical field guide for a Western Tasmania minerals and museums tour''
2001
Other unpaid people studied Tasmanian geology such as Paweł Edmund Strzelecki, Joseph Milligan who was a surgeon, R.M. Johnson,
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
,
John Lhotsky John Lhotsky (1795–1866) was a Galicia-born Austrian naturalist, lecturer, artist and author. He wrote and published on the topics of zoology, botany, geology, geography and politics. Lhotsky was active in the early colonies of New South Wales ...
and
Joseph Jukes Joseph Beete Jukes (10 October 1811 – 29 July 1869), born to John and Sophia Jukes at Summer Hill, Birmingham, England, was a renowned geologist, author of several geological manuals and served as a naturalist on the expeditions of (under th ...
. Joseph Milligan sent specimens of a manganese mineral from
Frenchman's Cap Frenchmans Cap is a mountain in the West Coast region of Tasmania, Australia. The mountain is situated in the Franklin-Gordon Wild Rivers National Park. At above sea level, it is within the top thirty highest mountains in Tasmania. Locatio ...
and
Galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It cryst ...
to the 1851
Great Exhibition The Great Exhibition of the Works of Industry of All Nations, also known as the Great Exhibition or the Crystal Palace Exhibition (in reference to the temporary The Crystal Palace, structure in which it was held), was an International Exhib ...
in London. Small amounts of gold were discovered at
Fingal Fingal ( ; ) is a county in Ireland. It is located in the province of Leinster and is part of the Eastern and Midland Region. It is one of three successor counties to County Dublin, which was disestablished for administrative purposes in 1994. ...
and Lefroy in 1851. William B. Clarke, a geologist and Anglican parson, predicted that gold would be found in Tasmania at 146 degrees east longitude line. On 17 July 1859 Charles Gould, a geologist recruited from England, was appointed as the Geological Surveyor of Tasmania by the Tasmanian governor. He began the search for worthwhile minerals in the west, gave up and studied the geology of the eastern half of the state instead. He was commissioned by the
Tasmanian Government The Tasmanian Government is the democratic administrative authority of the state of Tasmania, Australia. The leader of the party or coalition with the confidence of the House of Assembly, the lower house of the Parliament of Tasmania, is invite ...
in 1862 to return to the
west coast West Coast or west coast may refer to: Geography Australia * Western Australia *Regions of South Australia#Weather forecasting, West Coast of South Australia * West Coast, Tasmania **West Coast Range, mountain range in the region Canada * Britis ...
, he named mountains in the
West Coast Range The West Coast Range is a mountain range located in the West Coast region of Tasmania, Australia. The range lies to the west and north of the main parts of the Franklin-Gordon Wild Rivers National Park. The range has had a significant nu ...
: Mount Lyell after
Charles Lyell Sir Charles Lyell, 1st Baronet, (14 November 1797 – 22 February 1875) was a Scottish geologist who demonstrated the power of known natural causes in explaining the earth's history. He is best known as the author of ''Principles of Geolo ...
, Mount Darwin, Mount Huxley and opponents of Charles Darwin were commemorated with Mount Owen, Mount Sedgwick, and Mount Jukes. Gould returned several times but did not find worthwhile mineral deposits. James "Philosopher" Smith discovered the Mount Bischoff tin deposit, for many years the world's richest and largest, on 4 December 1871. This discovery inspired George Renison Bell to find more tin and other minerals in western Tasmania. Dally shortly thereafter found important gold reefs at Beaconsfield and at Lefroy in the northeast.Geoffrey Blainey: ''
The Peaks of Lyell ''The Peaks of Lyell'' is a book by Geoffrey Blainey, based on his University of Melbourne MA thesis originally published in 1954. It contains the history of the Mount Lyell Mining and Railway Company, and through association, Queenstown and f ...
'' Melbourne University Press 1967
In 1882, Gustav Thureau was appointed Inspector of Mines, later called Inspector and Mining Geologist. In 1889, the position became Geological Surveyor.
William Harper Twelvetrees William Harper Twelvetrees (1848 – 7 November 1919) was an English geologist who was important for the characterisation of the geology of Tasmania. Twelvetrees was born in Bedfordshire, England, in 1848, to industrialist Harper Twelvetree ...
took up the position. He established the Geological Survey library, and mineral and rock collection at the Queen Victoria Museum in Launceston. In 1883, the Mines Office was created from the Commissioners and registrars for mines and goldfields that worked in the Mines Branch of the Lands and Works Department. Bernard Shaw was appointed the Secretary for Mines. The Mines Office gained a Minister for Mines in 1894 and changed its name to Mines Department. Bernard Shaw later became the Police Commissioner. The Mines Department lost its separate existence in July 1989 when it was merged to the Department of Resources and Energy, which has since changed its name several times. The current name for the Mines Office is ''Mineral Resources Tasmania''.C. A. Bacon
''A Brief History of the Department of Mines – 1882 to 2000''
2001
Tannatt William Edgeworth David, a geologist working out of Sydney, was a proponent of the idea of Permo-Carboniferous glaciations. He studied the evidence for past glaciations in Tasmania. Professor S. Warren Carey established the Department of Geology at the
University of Tasmania The University of Tasmania (UTAS) is a public research university, primarily located in Tasmania, Australia. Founded in 1890, it is Australia's fourth oldest university. Christ College, one of the university's residential colleges, first pro ...
on 27 October 1946. He was an early proponent of continental drift and the unorthodox
expanding earth theory The expanding Earth or growing Earth hypothesis argues that the position and relative movement of continents is at least partially due to the volume of Earth increasing. Conversely, geophysical global cooling was the hypothesis that various featu ...
. He had become the Government Geologist of Tasmania in 1944 where he organised the understanding of Paleozoic formations in the west coast mineral fields, and introduced the Cenozoic rift valley idea, and the policy of publishing the results of the Geologic Survey. Carey introduced terms such as
orocline An orocline — from the Greek words for "mountain" and "to bend" — is a bend or curvature of an orogenic (mountain building) belt imposed after it was formed. The term was introduced by S. Warren Carey in 1955 in a paper setting forth how comp ...
and sphenochasm and the concept of the hotspot. The University of Tasmania building for Geology and Geography was constructed in 1962. It had exhibitions of a
Foucault pendulum The Foucault pendulum or Foucault's pendulum is a simple device named after French physicist Léon Foucault, conceived as an experiment to demonstrate the Earth's rotation. A long and heavy pendulum suspended from the high roof above a circular a ...
, a
seismometer A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu ...
recording drum, a mosaic illustrating crystal symmetry, and a large terrestrial globe. Carey organised and hosted the Continental Drift Symposium in 1956. The Tasmanian Seismic Net was established in 1957. Professor Carey founded the Tasmanian Caverneering Club. The film ''
Walking with Dinosaurs ''Walking with Dinosaurs'' is a 1999 six-part nature documentary television miniseries created by Tim Haines and produced by the BBC Science Unit the Discovery Channel and BBC Worldwide, in association with TV Asahi, ProSieben and France 3. Envi ...
'' was filmed in part in central Tasmania where forests of
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό ...
s similar to vegetation in the Cretaceous still grow.


References


Maps

* Geological Map of Tasmania 1:506,880 Geological Survey of Tasmania-Department of Mines 1961 * Geological Atlas 1:250,000 series SK55-3 Burnie Geological Survey of Tasmania-Department of Mines 1973 * Geological Atlas 1:250,000 series SK55-4 Launceston Geological Survey of Tasmania-Department of Mines 1975 * Geological Atlas 1:250,000 series SK55-5 Queenstown Geological Survey of Tasmania-Department of Mines 1975 * Geological Atlas 1:250,000 series SK55-6 Oatlands Geological Survey of Tasmania-Department of Mines 1975 * Geological Atlas 1:250,000 series SK55-7 Port Davey Geological Survey of Tasmania-Department of Mines 1976 * Geological Atlas 1:250,000 series SK55-8 Hobart Geological Survey of Tasmania-Department of Mines 1975
Mineral Resources Tasmania: Online maps


External links


Mineral Resources Tasmania

Geoscience Australia – Tasmanian TASGO 3D model
{{Geology of Australia