Geology of the Lake District
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The
geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...
of England's Lake District is dominated by
sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
and
volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...
s of mainly
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 ...
age underpinned by large
granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz- ...
intrusions. Younger sedimentary sequences outcrop on the edges of the Lake District area, with Silurian to the south, Carboniferous to the north, east and west and Permo-
Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
to the west and east. The entire area was covered by a
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 ...
sequence that was eroded off during Paleogene uplift related to the opening of the North Atlantic. During the Quaternary the area was affected by repeated
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 be ...
s, which sculpted the current mountainous landscape.


Early Paleozoic

In early
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 ' ...
times the area was on the northern margin of the
microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...
of Avalonia, which was moving northwards as the Iapetus Ocean began to close. Initial deepwater sedimentation recorded by the Skiddaw Group was followed by the development of a continental arc caused by the subduction of Iapetus
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 ...
beneath the Avalonian margin. This
magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...
produced both the
Borrowdale Volcanic Group The Borrowdale Volcanic Group is a group of igneous rock formations named after the Borrowdale area of the Lake District, in England. They are Caradocian (late Ordovician) in age (roughly 450 million years old). It is thought that they represent t ...
sequence and the older granitic intrusions, which are the preserved
magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it up ...
s to the volcanics. Continental collision began near the end of the Ordovician as southward subduction ceased and northward subduction beneath the margin of
Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...
began, forming the Southern Uplands
accretionary wedge An accretionary wedge or accretionary prism forms from sediments accreted onto the non- subducting tectonic plate at a convergent plate boundary. Most of the material in the accretionary wedge consists of marine sediments scraped off from the d ...
. As the collision progressed the Lake District area became part of a foreland basin in which the
Windermere Supergroup The Windermere Supergroup is a geological unit formed during the Ordovician to Silurian periods ~, and exposed in northwest England, including the Pennines and correlates along its strike, in the Isle of Man and Ireland, and down-dip in the South ...
sediments were deposited, initially interfingering with the volcanics and then overlaying them. The collision reached its end during the
Early Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, ...
, part of the Acadian Orogeny with the final closure of Iapetus and the intrusion of late orogenic granites.


Skiddaw Group

The Skiddaw Group are the oldest rocks known from the Lake District. They are mainly Ordovician in age, from possibly Cambrian up to
Llanvirn 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. Th ...
(upper middle Ordovician). The sequence, which is up to about 5 km in thickness, consist mainly of mudstones and siltstones, with lesser amounts of sandstone. Following deformation and low-grade metamorphism during the Acadian Orogeny, they now have a well-developed
slaty cleavage Cleavage, in structural geology and petrology, describes a type of planar rock feature that develops as a result of deformation and metamorphism. The degree of deformation and metamorphism along with rock type determines the kind of cleavage fea ...
, giving rise to their common name, the Skiddaw Slates. The group is divided into two main areas, the northern and central fells, to either side of the WSW-ENE trending Causey Pike Fault, with distinct successions developed.


Eycott Volcanic Group

The Eycott Volcanic Group (EVG) forms the youngest part of the preserved Ordovician sequence in the northernmost part of the Lake District. This set of mainly
andesitic 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 predomin ...
lavas and tuffs, with related minor intrusions is of Caradocian (
Sandbian The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species '' Nemagraptus gracilis'' around million yea ...
to Early
Katian The Katian is the second stage of the Upper Ordovician. It is preceded by the Sandbian and succeeded by the Hirnantian Stage. The Katian began million years ago and lasted for about 7.8 million years until the beginning of the Hirnantian millio ...
) age. In terms of their chemistry the EVG are transitional between moderately potassic
tholeiitic 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
calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...
in type.


Borrowdale Volcanic Group

The Borrowdale Volcanic Group (BVG) lies
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 ...
above the Skiddaw Group, and is of Caradocian age. It is similar to, but distinct from, the Eycott Volcanic Group. It consists of a thick sequence of
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 ...
ic, andesitic,
dacitic 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 rhyol ...
and
rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
lavas and
pyroclastic rock 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 ...
s with interbedded volcaniclastic sediments. It is subdivided informally into two parts known as the Lower Borrowdale Volcanic Group and Upper Borrowdale Volcanic groups. It is further subdivided into many formations, of which only a few have regional extent. In terms of chemistry, the BVG are moderate to highly potassic calk-alkaline in type.


Lower Borrowdale Volcanic Group

The lower part of the succession is dominantly andesitic. Locally in the western part, the lowest formation is the non-volcanic sandstones of the Latterbarrow Formation. In the Furness Inlier the Greenscoe Tuff Formation is the lowermost unit. In the southwest at Millom Park the Whinny Bank Tuff Formation is the lowermost unit, overlain by the Po House Tuff Formation. The Birker Fell Andesite Formation makes up most of the lower BVG, varying in thickness from 980 m to 2700 m.


Upper Borrowdale Volcanic Group

The upper part of the group consists of mainly intermediate to acidic pyroclastic rocks and interbedded volcaniclastic sediments. There are four main successions recognised at the base of the upper sequence: the Duddon Basin, the Scafell Caldera, the Haweswater Caldera and the Kentmere succession. These are all followed by volcaniclastic sandstone of the Seathwaite Fell Sandstone Formation, which is developed over almost the whole outcrop, varying in thickness from 30 m to >1100 m. This is followed by the equally extensive Lincombe Tarns Tuff Formation, which is an
ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...
. The uppermost part is the Helvellyn Basin succession, consisting of volcaniclastic sandstones, dacitic lavas, andesitic lavas and tuffs, and dacitic ignimbrites.


Windermere Supergroup

The transition from the top of the Borrowdale Volcanics into the overlying
Dent Group The Dent Group is a group of Upper Ordovician sedimentary and volcanic rocks in north-west England. It is the lowermost part of the Windermere Supergroup, which was deposited in the foreland basin formed during the collision between Laurentia an ...
is marked by an unconformity. The Dent Group is of latest Ordovician age and forms the lowermost part of the Windermere Supergroup. It was deposited in shallow marine conditions, consisting mainly of calcareous mudstones, siltstones, limestones and shales. There is evidence of continued volcanism, with tuffs locally developed at various levels within the group. The Dent Group is overlain unconformably by the Stockdale Group, a sequence of mudstones and siltstones deposited during the latest Ordovician to earliest Silurian. The overlying
Sheinwoodian In the geologic timescale, the Sheinwoodian is the age of the Wenlock Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that is comprehended between 433.4 ± 0.8 Ma and 430.5 ± 0.7 Ma (million years ago), approximatel ...
to
Gorstian In the geologic timescale, the Gorstian is an age of the Ludlow Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that is comprehended between 427.4 ± 0.5 Ma and 425.6 ± 0.9 Ma (million years ago), approximately. The ...
Tranearth Group The Tranearth Group is a Silurian lithostratigraphy, lithostratigraphic group (stratigraphy), group (a sequence of rock strata) in the southern Lake District and Howgill Fells of the Pennines of northern England. The name is derived from the loca ...
consists mainly of hemipelagite (clays and silts) with some turbiditic sandstones. This is succeeded by turbiditic sandstones, siltstones and hemipelagites of the Gorstian Coniston Group. The youngest unit is 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 ...
to Pridoli
Kendal Group The Kendal Group is a Silurian lithostratigraphic group (a sequence of rock strata) in the southern Lake District and the Howgill Fells of northern England. The name is derived from the town of Kendal in Cumbria. The Group is included within the ...
, which consists of couplets of graded siltstone and mudstone, locally with thick turbiditic sandstones.


Granitic intrusions

The Lake District was affected by two stages of granitic intrusion. The earlier Ordovician granites were intruded at the same time as the BVG, representing the solidified magma chambers related to the volcanics, which later uplift has now exposed at the surface. Intrusions of this age include the Ennerdale Granophyre and the Eskdale Granite. The later granites were intruded during the Early Devonian as part of group of intrusions found within a SW–NE trending belt that straddles the
Iapetus Suture The Iapetus Suture is one of several major Fault (geology), geological faults caused by the collision of several ancient land masses forming a suture (geology), suture. It represents in part the remains of what was once the Iapetus Ocean. Iapet ...
. Granites of this age include the
Shap Shap is a linear village and civil parish located among fells and isolated dales in Eden district, Cumbria, England, in the historic county of Westmorland. The parish had a population of 1,221 in 2001, increasing slightly to 1,264 at the 2011 ...
Granite, the Skiddaw Granite and the unexposed granite responsible for the
Crummock Water Crummock Water is a lake in the Lake District in Cumbria, North West England situated between Buttermere to the south and Loweswater to the north. Crummock Water is long, wide and deep. The River Cocker is considered to start at the north of ...
aureole An aureola or aureole (diminutive of Latin ''aurea'', "golden") is the radiance of luminous cloud which, in paintings of sacred personages, surrounds the whole figure. In Romance languages, the noun Aureola is usually more related to the d ...
. As a result of these two separate magmatic events, the Lake District is underpinned by a large batholith with an area of about 1500 km2. Most of the batholith is thought to be Late Ordovician in age but with some Early Devonian contributions.


Late Paleozoic

After the end of the Acadian collision, Northern England was affected by a phase of Early Carboniferous extension, possibly related to the subduction of
Rheic Ocean The Rheic Ocean was an ocean which separated two major palaeocontinents, Gondwana and Laurussia (Laurentia- Baltica-Avalonia). One of the principal oceans of the Palaeozoic, its sutures today stretch from Mexico to Turkey and its closure result ...
crust beneath Gondwana. Preserved Lower Carbonifeous rocks are found to the west, north and east of the Lake District in the East Irish Sea, Solway and
Vale of Eden The Vale of Eden is formed by the course of the River Eden, one of the major rivers of Northwest England. It is however of much greater extent than the actual valley of the river, lying between the Cumbrian Mountains (more usually referred to as ...
basins. The sequence consists of limestones of the Carboniferous Limestone Supergroup, overlain by sandstones of the Millstone Grit Group and deltaic sandstones, shales and coals of the Coal Measures Group. The only Permian rocks known from the Lake District area are from the upper part of the sequence and form part of the early
syn-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 Fault (geology), downfaulted depression, called a graben, or more commonly ...
associated with the mainly Triassic
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 ...
ing event. This sequence consists of the Appleby Group, dominantly sandstones, and the Cumbrian Coast Group consisting mainly of siltstones and
dolomites The Dolomites ( it, Dolomiti ; Ladin: ''Dolomites''; german: Dolomiten ; vec, Dołomiti : fur, Dolomitis), also known as the Dolomite Mountains, Dolomite Alps or Dolomitic Alps, are a mountain range located in northeastern Italy. They form pa ...
overlain by
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 red shales (locally with the development of
halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
). On the western edge of the Lake District and in the Vale of Eden the Appleby Group includes thick
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 ...
s, known as the Brockram.


Mesozoic

The Mesozoic saw the first stages of break-up of the
supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...
of
Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
. Rifting began at the end of the Permian, with development of a series of rift basins over much of the British Isles. The rifts became more localised during the Jurassic and by the Cretaceous, most of the rifting has stopped, apart from the area south of the Variscan Front, where rifting continued into the Early Cretaceous. The Late Cretaceous saw the inundation of almost all parts of the British Isles by the "chalk sea". Triassic age rocks of the
New Red Sandstone The New Red Sandstone, chiefly in British geology, is composed of beds of red sandstone and associated rocks laid down throughout the Permian (300  million years ago) to the end of the Triassic (about 200 million years ago), that under ...
outcrop to the northeast and southwest of the Lake District massif. To the southwest they were deposited at the eastern edge of the
East Irish Sea Basin The Irish Sea or , gv, Y Keayn Yernagh, sco, Erse Sie, gd, Muir Èireann , Ulster-Scots: ''Airish Sea'', cy, Môr Iwerddon . is an extensive body of water that separates the islands of Ireland and Great Britain. It is linked to the Ce ...
. To the northeast, they were deposited in the Vale of Eden Basin. The Triassic sequences consist mainly of continental sandstones. At the end of the Triassic, shallow seas transgressed over all of the Triassic basins. There are no rocks of Jurassic or Cretaceous age preserved anywhere near the Lake District. However, based on the analysis of apatite fission tracks (AFTA) and estimates from neighbouring preserved sequences, it is thought that the Lake District was covered by between about 700 to 1750 m of Triassic, Jurassic and Cretaceous sediments by the Palaeocene that has since been removed by erosion.


Cenozoic

During the Paleogene, the Lake District, like most of the northern and western British Isles was affected by the break-up of the Atlantic at the end of the Paleocene, including the formation of the
North Atlantic Igneous Province The North Atlantic Igneous Province (NAIP) is a large igneous province in the North Atlantic, centered on Iceland. In the Paleogene, the province formed the Thulean Plateau, a large basaltic lava plain, which extended over at least in area and i ...
. The timing of the exhumation that removed the Mesozoic section from the top of the Lake District massif remains uncertain, although a significant part of the uplift is thought to have been caused by underplating at the end of the Paleocene. The amount of Neogene exhumation is particularly poorly constrained.


Quaternary

The Quaternary saw repeated glaciations of the Lake District area with the development of an ice cap, although the current landscape is the result of the Last glacial period, which occurred over the period 115,000 to 11,700 years ago. As the Lake District was an upland area it was unaffected by the main British-Irish ice sheet, which flowed around the margins of the massif.


Devensian glaciation

The main period of glaciation to shape the Lake District was the Devensian (the British name for the last glacial period). There were undoubtedly earlier glacial phases, but all signs of them were removed by erosion associated with the Devensian phase. The radial pattern of the main deeply glaciated valleys is thought to reflect the original radial pre-glacial drainage pattern of the massif. At various times, the peaks were either completely covered by ice or formed protruding nunataks.


Younger Dryas

Some of the best preserved glacial deposits were formed during the
Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stag ...
stadial Stadials and interstadials are phases dividing the Quaternary period, or the last 2.6 million years. Stadials are periods of colder climate while interstadials are periods of warmer climate. Each Quaternary climate phase is associated with a Ma ...
, which followed on from the relatively warm
Late Glacial Interstadial The Late Glacial Interstadial (LGI) c. 14,670 to c. 12,890 BP, also called the Bølling–Allerød interstadial, represents the first ''pronounced'' warming since the end of the Last Glacial Maximum (LGM). Human populations, which had previousl ...
about 12,900 years ago. A this time permanent ice reappeared in the Lake District. At its maximum the ice is thought to have been in the form of two areas of plateau glaciation in the central and eastern fells.


Structure


Pre-Acadian

The earliest known structures that affected the rocks of the Lake District are folds in the Skiddaw Group that are thought to be a result of slumping. It has also been proposed that there were active
extensional fault An extensional fault is a fault caused by stretching of the Earth's crust. Stretching reduces the thickness and horizontally extends portions of the crust and/or lithosphere. In most cases such a fault is also a normal fault, but may create a ...
s during deposition of the group, consistent with the presence of two distinct sequences. In this model, the Causey Pike Fault is one of the early faults, which was reactivated during the Acadian Orogeny as a thrust. The eruption of the Borrowdale Volcanic Group was accompanied by volcano-tectonic faulting. The faults of this age are extensional in type and thought to be a result of
caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...
formation.


Acadian

The main period of structuring was of Early Devonian age and part of the Acadian Orogeny. Most of the finer-grained sedimentary rocks in the Ordovician sequence took on a well-developed slaty cleavage. In the BVG, strong cleavage is mainly restricted to finer-grained volcaniclastic rocks interbedded with the volcanics. The rocks of the Windermere Supergroup have a variably developed cleavage. The cleavage has an overall WSW-ENE trend, although regionally it is somewhat arcuate, being more SW-NE trending in the west and more west-east trending in the east. The main Acadian structures in the Skiddaw Group are a set of
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 ...
s, of which the Causey Pike Fault has the greatest extent, being recognised across the whole of the main outcrop of the group. This and other thrusts within the Skiddaw Group are thought to be reactivated extensional faults that were active during sedimentation. The Borrowdale Volcanic Group sequence was folded during the Acadian and some of the volcano-tectonic faults were reactivated. Three large synclinal folds were formed, the Haweswater, Scafell and Ulpha synclines. In all cases, these synclines are thought to be modifications of older volcano-tectonic features. The southernmost part of the BVG sequence and the overlying Windermere Supergroup dip steeply to the south forming the Westmorland Monocline. Continuing to the south a series of upright folds are developed, reducing in amplitude towards the south. The first and largest of the folds is the Bannisdale Syncline.


Post-Acadian

During the Carboniferous period, the Lake District massif initially formed an emergent high. The north-dipping Maryport Fault formed on its northern margin as part of the regional Early Carboniferous extensional event, possibly reactivating an Acadian thrust structure. It was reactivated during the
Variscan Orogeny The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Variscan'', comes f ...
as a reverse fault, leading to
inversion Inversion or inversions may refer to: Arts * , a French gay magazine (1924/1925) * ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas * Inversion (music), a term with various meanings in music theory and musical set theory * ...
of the Solway Basin to the north. The Lake District Boundary Fault on the western margin may also have been active at this time, possibly reactivating an Ordovician volcano-tectonic fault in part. In late Permian to Triassic times the Lake District Boundary Fault was an active extensional structure, forming part of the margin to the East Irish Sea Basin. Activity on this structure continued episodically through the Triassic up to the Early Cretaceous.


Mineralisation

Mineralisation has affected all of the Ordovician rocks in the Lake District, whether sedimentary, volcanic or intrusive. The distribution of this mineralisation suggests a close relationship to the batholith that underlies the area. The mineral veins indicate that there were several separate periods of mineralisation, with each period being associated with particular minerals.


Graphite

At Seathwaite there is major deposit of
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...
. The graphite appears as pipes and veins associated with a
diorite Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-sili ...
intrusion, presumed to be of Caradoc age. Organic-rich sediments in the Skiddaw Group mudstones are considered the likely source for the carbon. These high-temperature veins were probably deposited from aqueous fluids rich in carbon dioxide and methane driven by the effects of the dioritic intrusion.


Copper

Copper mineralisation is mainly hosted by the Borrowdale Volcanic Group, with particularly important veins found in the Coniston,
Haweswater Haweswater is a reservoir in the valley of Mardale, Cumbria in the Lake District, England. Work to raise the height of the original natural lake was started in 1929. It was controversially dammed after the UK Parliament passed a Private Act ...
and
Ulpha Ulpha is a small village and civil parish in the Duddon Valley in the Lake District National Park in Cumbria, England. Historically in Cumberland, it forms part of the borough of Copeland. At Ulpha a road leaves the Duddon Valley to cross Bir ...
areas. The main copper mineral found is
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 ...
, locally accompanied by
bornite Bornite, also known as peacock ore, is a sulfide mineral with chemical composition Cu5 Fe S4 that crystallizes in the orthorhombic system (pseudo-cubic). Appearance Bornite has a brown to copper-red color on fresh surfaces that tarnishes to v ...
,
chalcocite Chalcocite (), copper(I) sulfide (Cu2S), is an important copper ore mineral. It is opaque and dark gray to black, with a metallic luster. It has a hardness of 2.5–3 on the Mohs scale. It is a sulfide with a monoclinic crystal system. ...
and
tennantite Tennantite is a copper arsenic sulfosalt mineral with an ideal formula . Due to variable substitution of the copper by iron and zinc the formula is . It is gray-black, steel-gray, iron-gray or black in color. A closely related mineral, tetrahedri ...
. The veins also contain arsenic and iron sulphides, and locally magnetite. Other minerals in minor to trace amounts include
native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and entert ...
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 ...
, other bismuth minerals and locally gold. The veins typically have chlorite,
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
and
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 ...
as
gangue In mining, gangue () is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body ...
minerals. The veins were probably deposited from moderately saline brines, with the metallic elements derived from the volcanics and the sulphur from the underlying Skiddaw Group. This period of mineralisation probably dates to the late Caradoc as the veins clearly predate the Acadian-aged cleavage.


Tungsten

North-south trending veins containing the tungsten minerals
scheelite Scheelite is a calcium tungstate mineral with the chemical formula Ca W O4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist K. Scheele (1742-1786). Well-formed crystals are sought by collectors ...
and
wolframite Wolframite is an iron, manganese, and tungstate mineral with a chemical formula of that is the intermediate between ferberite ( rich) and hübnerite ( rich). Along with scheelite, the wolframite series are the most important tungsten ore mineral ...
are associated with the Skiddaw granite around Carrock Fell in the northern lakes. Associated
molybdenite Molybdenite is a mineral of molybdenum disulfide, Mo S2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum ato ...
gives Re-Os age of 405 Ma (Early Devonian), similar in age to the Skiddaw intrusion (399 Ma). The veins are thought to have been deposited from moderately saline brines rich in tungsten.


Lead-zinc

Lead-zinc mineralisation is found over most of the Ordovician outcrop, but particularly in the northern part. The greatest number of veins is found at Brandlehow, in the
Caldbeck Fells Caldbeck is a village in Cumbria, England, historically within Cumberland, it is situated within the Lake District National Park. The village had 714 inhabitants according to the census of 2001. Caldbeck is closely associated with neighbouring ...
, at Eagle Crag, Force Crag, Greenside,
Hartsop Hartsop is a small village in the English Lake District. It lies in the Patterdale valley, near Brothers Water, Hayeswater and Kirkstone Pass. It consists of 17th-century grey stone cottages, like so many of its neighbours. Hartsop retains ...
,
Helvellyn Helvellyn (; possible meaning: ''pale yellow moorland'') is a mountain in the English Lake District, the highest point of the Helvellyn range, a north–south line of mountains to the north of Ambleside, between the lakes of Thirlmere and Ul ...
, around
Threlkeld Threlkeld is a village and civil parish in the north of the Lake District in Cumbria, England, to the east of Keswick. It lies at the southern foot of Blencathra, one of the more prominent fells in the northern Lake District, and to the nort ...
, Thornthwaite and the
Newlands Valley The Newlands Valley is in the Lake District National Park in Cumbria, England. It is regarded as one of the most picturesque and quiet valleys in the national park, even though it is situated very close to the popular tourist town of Keswick and ...
. The main minerals are galena and sphalerite. The galena locally contains up to 838 ppm of silver. Common gangue minerals are baryte, calcite, dolomite and quartz, locally with
siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...
and
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 ...
. Estimated temperatures for these veins is in the range 110–130 °C. The lead and zinc are thought to have been derived by the leaching of Skiddaw Group rocks, the underlying batholith or Carboniferous sediments of the Solway Basin, by Carboniferous seawater. These veins are seen to cut copper-bearing veins and they are thought to be either Late Carboniferous to Early Permian in age, consistent with the age of similar veins in the northern Pennines, or Permo-Triassic in age, similar to the haematite mineralisation.


Iron

Iron mineralisation, in the form of haematite veins, occurs across the northern and western Lake District, hosted particularly in the Skiddaw Group slates. It is typically of the form known as "kidney ore" with most of the veins being almost pure haematite. The most significant haematite mineralisation, however, is in the form of large orebodies replacing Carboniferous limestone in the West Cumbrian iron orefield on the western margin of the Lake District. The similarities between the orebodies hosted in the limestone and those in the Ordovician rocks suggests that they were formed together. The most likely source for the iron is the Permo-Triassic sequence that lies to the west of the Lake District in the East Irish Sea Basin. Orebodies are concentrated wherever Carboniferous limestone is in direct contact with permeable Permo-Triassic rocks. The same iron-rich fluids moving eastwards away from the basin within the sedimentary cover sequence would then have had access to open fractures in the Ordovician rocks, forming the vein deposits there.


Other minerals

The
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
minerals
alloclasite Alloclasite () is a sulfosalt mineral ( IMA symbol: Acl). It is a member of the arsenopyrite group. Alloclasite crystallizes in the monoclinic system and typically forms as columnar to radiating acicular prismatic clusters. It is an opaque steel-g ...
,
cobaltite Cobaltite is a sulfide mineral composed of cobalt, arsenic, and sulfur, Co As S. Its impurities may contain up to 10% iron and variable amounts of nickel.Klein, Cornelus and Cornrlius Hurlbut, 1996, ''Manual of Mineralogy'', 20th ed., Wiley, p. ...
, glaucodot and
skutterudite Named after Skuterudåsen, a hill in Modum, Norway, skutterudite is a cobalt arsenide mineral containing variable amounts of nickel and iron substituting for cobalt with the ideal formula CoAs3. Some references give the arsenic a variable formula ...
have been found in very small amounts associated with apatite-chlorite veins near Causey Pike.
Tourmaline Tourmaline ( ) is a crystalline 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 of colors. The te ...
is found associated with some of the granites and in the Crummock Water aureole.
Antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient t ...
, mainly in the form of
stibnite Stibnite, sometimes called antimonite, is a sulfide mineral with the formula Sb2 S3. This soft grey material crystallizes in an orthorhombic space group. It is the most important source for the metalloid antimony. The name is derived from the ...
, is found in a minor group of veins affecting the Skiddaw Group and the BVG. Baryte, a common gangue mineral in the lead-zinc veins, locally becomes the dominant mineral in veins in the Caldbeck Fells and Force Crag. Small amounts of gold have also been found.


Economic geology

The Lake District has a long history of mining and quarrying going back to at least
Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several p ...
times, with the stone axe factory at Langdale. There are very few active mines or quarries in the Lake District at present, with the quarries working the
Shap Shap is a linear village and civil parish located among fells and isolated dales in Eden district, Cumbria, England, in the historic county of Westmorland. The parish had a population of 1,221 in 2001, increasing slightly to 1,264 at the 2011 ...
Granite being a notable exception.


Mining

The earliest records of mineral extraction in the Lake District is evidence of haematite mining in the Iron Age in
Furness Furness ( ) is a peninsula and region of Cumbria in northwestern England. Together with the Cartmel Peninsula it forms North Lonsdale, historically an exclave of Lancashire. The Furness Peninsula, also known as Low Furness, is an area of vill ...
and during
Roman times In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 BC ...
in West Cumbria. Many mines were active from the 16th-century, following the involvement of the
Society of Mines Royal The Society of the Mines Royal was one of two English mining monopoly companies incorporated by royal charter in 1568, the other being the Company of Mineral and Battery Works. History On 28 May 1568, Elizabeth I established the Society by let ...
, who brought in German miners for their expertise.


Caldbeck Fells

There are more than a dozen individual mines in the area of the
Caldbeck Caldbeck is a village in Cumbria, England, historically within Cumberland, it is situated within the Lake District National Park. The village had 714 inhabitants according to the census of 2001. Caldbeck is closely associated with neighbouring ...
Fells, which were an important source of copper, lead, arsenic, baryte and tungsten from the 16th century up to the 1980s. The larger copper mines included Mexico Mine, Red Gill Mine, Roughton Gill Mine and Silver Gill Mine. Carrock Fell Mine was the last in the area to remain active and the only one to produce wolfram and scheelite in England outside Devon and Cornwall.


Goldscope mine

Although there is evidence of small-scale near-surface mining in the
Newlands Valley The Newlands Valley is in the Lake District National Park in Cumbria, England. It is regarded as one of the most picturesque and quiet valleys in the national park, even though it is situated very close to the popular tourist town of Keswick and ...
area from the 13th-century, mining on a large scale began in 1564. The german miners brought in to work it by the Mines Royal named it "Gottesgab" (God's gift) due to the richness of the copper deposit, which became corrupted over time to "Goldscope". During the 16th and 17th centuries it was worked for copper, but became disused during the 18th century. It was reopened for lead mining during the 19th century, before final closure in 1920.


Force Crag

This mine, at the head of the Coledale valley, was initially opened in the mid-19th century to produce lead and silver. From 1867 until its closure in 1991 it was worked mainly for baryte and zinc. The mine produced 60,000 tons of baryte during its working life.


Seathwaite graphite mine

Near Seathwaite in
Borrowdale Borrowdale is a valley and civil parish in the English Lake District in the Borough of Allerdale in Cumbria, England. It lies within the historic county boundaries of Cumberland. It is sometimes referred to as ''Cumberland Borrowdale'' ...
an unusually large deposit of high quality graphite, known locally as "wad", was found in the form of veins. Although the deposit was known from at least the early 15th century, significant production only began in the early 17th century and continued until 1891, when the mine finally closed. The very irregular geometry of the veins led to a complex set of workings. Individual pods of graphite could be quite large. For example, Dixon's Pipe, discovered in 1803, generated more than 30 tons of graphite, at more than £1300 per ton.


West Cumbrian iron orefield

Large deposits of hematite hosted in Carboniferous Limestone, were exploited by a series of mines on the northwestern margin of the Lake District. The
Cleator Moor Cleator Moor is a town and civil parish in Cumbria, England, within the historic county of Cumberland. It had a population of 6,936 at the 2011 census. Below Dent Fell, the town is on the Coast to Coast Walk that spans Northern England. ...
to Egremont area was particularly important, with Bigrigg, just north of Egremont, being the earliest for which there are written records, showing that this area was active as early as 1179. At the Langhorn Mine, a large high quality orebody was found, which had produced 12,500 tons of ore by 1709. In the 20th century, exploration between Egremont and Haile led to the development of three separate mines, Ullcoats, Florence and Beckermet, that were eventually linked together. This combined mine was the last to be active in West Cumbria, carrying on until 2008, if only on a small scale, when flooding brought operations to a final halt.


Coniston

The Mines Royal began working on the copper deposits near Coniston at the end of the 16th century until 1642, when mining was interrupted by the
civil war A civil war or intrastate war is a war between organized groups within the same state (or country). The aim of one side may be to take control of the country or a region, to achieve independence for a region, or to change government policies ...
. It did not begin again in earnest until 1758, when the Macclesfield Copper Company started to work the Bonsor Vein, continuing to a depth below the surface of by 1795, where work once again stopped. In 1824 the experienced mining engineer John Taylor oversaw a major expansion of the mine and by 1856, the mine had its most productive year, with an output of 3,659 tons of ore. From that peak, output dropped off rapidly and by the end of the century virtually all mining activity had stopped.


Building stone

Various of the rock types in the Lake District have been quarried for building stone.


Slate

The Skiddaw Group slates have mainly been used in buildings around its area of outcrop as
rubble stone Rubble stone is rough, uneven building stone not laid in regular courses. It may fill the core of a wall which is faced with unit masonry such as brick or ashlar. Analogously, some medieval cathedral walls are outer shells of ashlar with an i ...
as the slates are of too low quality for use in roofing. The strongly cleaved volcaniclastic units (
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 ...
s) within the BVG have in contrast locally produced good quality slates that have been widely quarried and more recently extracted by mining. Several different bands of slate have been worked across the outcrop, for instance at
Buttermere Buttermere is a lake in the Lake District in North West England. The adjacent village of Buttermere takes its name from the lake. Historically in Cumberland, the lake is now within the county of Cumbria. Owned by the National Trust, it forms pa ...
, along Borrowdale (Honister, Yewcrag, Rigg Head and Castle Crag) and from the
Duddon Estuary The Duddon Estuary is the sandy, gritty estuary of the River Duddon that lies between Morecambe Bay and the North Lonsdale coast. The River Duddon and its estuary form part of the boundary of the historic county of Lancashire. It opens into th ...
up to Mosedale (including
Broughton Moor Broughton Moor is a village and civil parish in Cumbria, England. It is situated on an extensive moor about north of Broughton, north west of Cockermouth, south of Maryport and north of Workington. According to the 2001 census it had a ...
, Kirskstone and Coniston). Light green, silver grey and blue-black varieties have all been worked. They have been used for roofing both in the Lake District and elsewhere in the United Kingdom. The
Honister Slate Mine The Honister Slate Mine in Cumbria is the last working slate mine in England. Quarrying for Westmorland green slate has been taking place in the area since 1728. Apart from the mining it is also a popular tourist attraction in the Lake Distr ...
is the only mine in the Lake District still producing slates of this type. Good quality slates are also found in parts of the Windermere Supergroup, particularly the blue-grey slates of the Tranearth Group, known as "Burlington Slates". These have been produced in large quantities since the 17th century. A large quarry working these slates is still in operation near
Kirkby-in-Furness Kirkby-in-Furness, generally referred to simply as Kirkby locally, is a village in the Furness area of Cumbria, England. Historically part of Lancashire, it's located close to the Lake District National Park. It is about south of Broughto ...
.


Limestone

Limestone has been quarried from the Carboniferous sequences on the margins of the Lake District. It has been mainly used as rubble stone or ashlar in buildings across the area, particularly in Kendal.


Sandstone

Sandstones of Carboniferous, Permian and Triassic age have all been used as building stone in the Lake District. Grey sandstones of the Yoredale Group were locally quarried and used in buildings. Red Penrith Sandstone and Brockram
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 ...
of the Permian Appleby Group have been used as building stone in the area of their outcrop to the east and south of the Lake District. Red Triassic sandstones of the
Sherwood Sandstone Group The Sherwood Sandstone Group is a Triassic lithostratigraphic group (a sequence of rock strata) which is widespread in Britain, especially in the English Midlands. The name is derived from Sherwood Forest in Nottinghamshire which is underlain by ...
were widely quarried, with the largest quarries near St Bees, working since the 19th century, sending stone around the country and to the United States.


Granitic rocks

Most of the Ordovician and Devonian granitic bodies in the Lake District have been quarried to some extent. Parts of the Eskdale granitic body has been worked for building stone, as seen in
Muncaster Castle Muncaster Castle is a privately owned castle overlooking the River Esk, about a mile east of the west-coastal town of Ravenglass in Cumbria, England. It is recorded in the National Heritage List for England as a designated Grade I listed ...
. The church of St James in Buttermere was partly constructed from rock taken from the Eskdale intrusion. The microgranite at
Threlkeld Threlkeld is a village and civil parish in the north of the Lake District in Cumbria, England, to the east of Keswick. It lies at the southern foot of Blencathra, one of the more prominent fells in the northern Lake District, and to the nort ...
was used in the Roman Catholic Our Lady of the Lakes and St Charles Church in Keswick. The Shap Granite has been quarried since the 19th century and still remains active, producing small amounts of ornamental stone.


Aggregate

Aggregate comes from three main types of extraction: unconsolidated sand and gravel, crushed rock aggregate and secondary aggregate (by-products of other types of extraction or industrial processes).


Sand and gravel

There are working sand and gravel quarries in Cumbria, but all outside the National Park, such as Peel Place Quarry, which works fluvioglacial sand and gravel, near
Holmrook Holmrook is a linear village in the English county of Cumbria. It lies along the A595 road on the west banks of the River Irt. The B5344 road connects it to Drigg, with its railway station less than two miles to the west. Two miles north-e ...
and Cardewmires Quarry which works river deposits south west of Carlisle.


Crushed rock aggregate

Much of the crushed rock aggregate in the area comes from various layers in the Carboniferous limestone. Higher specification aggregates, such as those required for
road surfacing A road surface (British English), or pavement (American English), is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, hoggin, cobble ...
, however, come mainly from sandstones and igneous rocks, both volcanic (BVG) and intrusive (various granitic bodies). Two quarries at Roan Edge (east of Kendal) and Holmscales are currently producing high specification roadstone from sandstone. The single quarry producing very high specification aggregate is at Ghyll Scaur, just north of
Millom Millom is a town and civil parish on the north shore of the estuary of the River Duddon in southwest Cumbria, historically part of Cumberland, England. It is situated just outside the Lake District National Park, about north of Barrow-in-Furnes ...
, which is the only currently available source for this quality of roadstone in England. It works a welded rhyolitic tuff from the Waberthwaite Tuff Formation of the BVG.


References

{{Geology of national parks in Britain


External links


Lake District National Park Authority's Geology Factsheet
Lake District Geology of Cumbria