The

island of Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The island of Taiwan, formerly known to Westerners as Formosa, has an area of and makes up 99% of the land under ROC control. It lies about across the Taiwan Strait f ...

was formed approximately 4 to 5 million years ago at a

convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

between the

Philippine Sea Plate The Philippine Sea plate or the Philippine plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part of ...

and the Eurasian Plate. In a boundary running the length of the island and continuing southwards, the Eurasian Plate is sliding under the Philippine Sea Plate. In the northeast of the island, the Philippine Sea Plate slides under the Eurasian Plate. Most of the island comprises a huge

fault block Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by Tectonics, tectonic and localized stresses in Crust (geology), Earth's crust. Large areas of bedrock are broken up into blocks by Fault (geology) ...

tilted to the west. The island is active geologically, formed on a complex convergent boundary between the Yangtze Subplate of the Eurasian Plate to the west and north, the Okinawa Plate on the north-east, the

on the east and south, and the Sunda Plate to the southwest.

Subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

changes direction at Taiwan. The upper part of the crust on the island is primarily made up of a series of

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its d ...

s, mostly old

island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...

s which have been forced together by the collision of the forerunners of the Eurasian Plate and the Philippine Sea Plate, which is moving to the northwest. These have been further uplifted as a result of the detachment of a portion of the Eurasian Plate as it was subducted beneath remnants of the Philippine Sea Plate, a process which left the crust under Taiwan more buoyant. South of Taiwan, the Sunda Plate is subducting under the Philippine Sea Plate, forming the

Luzon Volcanic Arc The Luzon Volcanic Arc is a volcanic arc, chain of volcanoes in a north–south line across the Luzon Strait from Taiwan to Luzon. The name "Luzon Volcanic Arc" was first proposed by Carl Bowin et al. to describe a series of Miocene to recent vo ...

(including Green Island and Orchid Island). The east and south of the island are a complex system of belts formed by, and part of the zone of, active collision between the North Luzon Trough portion of the Luzon Volcanic Arc and the Eurasian Plate, where accreted portions of the Luzon Arc and Luzon forearc form the eastern Coastal Range and parallel inland Taitung Longitudinal Valley of Taiwan respectively. From the northeast of Taiwan and continuing eastwards in the

Ryukyu The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Geography of Taiwan, Taiwan: the Ryukyu Islands are divided into the Satsunan Islands (Ōsumi Islands, Ōsumi, Tokara Islands, Tokara and A ...

Volcanic Arc, the Philippine Sea Plate is subducting under the Okinawa Plate, forming the Ryukyu Volcanic Arc. Taiwan seismicity

Terranes

The Hai'an Range or Coastal Range

belongs to the

(呂宋島火山弧), and is on the

(菲律賓海板塊). West of this is the Longitudinal Valley or Huatung Valley, an active depositional zone in a rift valley. West of this is the Eastern Central Range terrane, part of the continental base that has been upturned. The western side of the range is the Western Central Range terrane, which is metamorphosed earlier Tertiary clastic sediments. The Lishan Fault separates the Hsuehshan Range terrane Eocene to Oligocene sandstone and shale. The Chukou Fault (觸口斷層) provides the boundary for the Western Foothills terrane, which is shallow marine detritus from Miocene to Pleistocene. A deformation front forms the boundary with the undeformed coastal plains alluvium, which is still depositing. The Eastern Central Range terrane can be divided into the Tailuko belt on the west with greenschist metamorphism and the Yuli belt on the east with blueschist metamorphism. The two metamorphic belts are possibly separated by a fault called Shoufeng fault, but this is unproven.

Central Mountains

The oldest exposed rocks are heavily metamorphosed and found in the Central Mountains. Poor quality fossil evidence suggests an origin in the

Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...

Period. They form a band of rock from Nan'ao in the north to inland of Jinfeng on the eastern flank of the Central Mountain Range. The band is 30 km wide in the north and narrows to the south. These earlier rocks are heavily metamorphosed. They also occur as a basement beneath the western part of the island. They make up the Danana'ao Group or Tananao Schist. This group consists of the Kainanagang Gneiss, Tailuge Marble, and Changchun Schist. The Yuli Schist is

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

in age and consists of black schist and some

greenschist 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 ...

, glaucophane

schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

, and spotted

slate Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism. It is the finest-grained foliated metamorphic ro ...

. It is the easternmost part and extends from Chian southwards to the west of the Chihpen hot springs in a belt about 150 km long. Although the dark colour of the black schist is due to carbon, carbon is less than 2% of the content. The minerals found are quartz,

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), 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 s ...

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 tectosilicat ...

sphene Titanite, or sphene (), is a calcium titanium nesosilicate mineral, Ca Ti Si O5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly rep ...

, and

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

. The Changchun Schist being mostly

is found on the western side and forms thick beds. It is found along with smaller amounts of

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 prec ...

, and black schist. The rock is foliated dark green rock containing chlorite,

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 ha ...

, quartz, calcite, biotite, albite and actinolite. They are derived from

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

volcanic rock Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...

s. These rocks can host copper sulfide ores. Siliceous schists are coloured grey, they are metamorphosed sandstone, rich in quartz.

Quartzite Quartzite is a hard, non- foliated metamorphic rock that 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 tecton ...

and chert bands can be found, and they are commonly associated with the black schist. The Chiuchu Formation or Tailuge Marble forms a band from Tailuko in the north to a point between Wulu and Kuanshan in the south. The

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

is mined in quarries south of Suao for cement manufacture. Although the colour is usually a shade of grey, there are also black or white limestone, which is chopped into blocks for building purposes. dolomite is also found along with the limestone particularly at Chingchangshan, Hopingchi, and Mukuashan. The Kainangan Gneiss or Kanagan Formation occurs in several elongated bodies. The

gneiss Gneiss (pronounced ) 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. This rock is formed under p ...

derived from sedimentary rocks contains coarse grained quartz, biotite, and albitic plagioclase. There is also orthogneiss derived from

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, 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 coo ...

. This is light grey and contains sodic plagioclase, quartz, biotite, and muscovite. Within the gneiss there are

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

dikes containing quartz, feldspar and mica. Other igneous rocks found in the old metamorphic belt are

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 ...

and

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 ...

dikes.

Serpentinite Serpentinite is a metamorphic rock composed predominantly of serpentine group minerals formed by serpentinization of mafic or ultramafic rocks. The ancient origin of the name is uncertain; it may be from the similarity of its texture or color ...

is found 5 km west of Fengtien (奉天). It contains exploited deposits of nephrite,

talc Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

and

asbestos Asbestos ( ) is a group of naturally occurring, Toxicity, toxic, carcinogenic and fibrous silicate minerals. There are six types, all of which are composed of long and thin fibrous Crystal habit, crystals, each fibre (particulate with length su ...

. Wanjung Station (萬榮) is close to more outcrops of serpentenite. Tamayenshan block northwest of Juisui (瑞穗) and the Tsenghuanshan block 10 km west of Juisui are significant

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 usua ...

outcrops. Green serpentinite from near Yuli makes a good quality building stone. A band of ultramafic rocks extends for 25 km north of Litao, Taitung (離島). The area was subjected to the Nanao Orogeny around 85 Ma which involved the granite intrusion and regional metamorphism. Rifting that opened the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan island, Taiwan and northwestern Philippines (mainly Luz ...

around 40 Ma may be connected with some dolerite intrusions. The Penglai Orogeny started about 10 Ma and continues at the present time.

Eastern stratigraphic region

The most recently added part of the island is the Coastal Range on the east coast from

Taitung City Taitung City () is a county-administered city and the county seat of Taitung County, Taiwan. It lies on the southeast coast of Taiwan facing the Pacific Ocean. Taitung City is the most populous subdivision of Taitung County and it is one of the ...

in the south to Hualien City in the north. The range is the continuation of the Luzon arc. The age is

Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...

and the rock consist of melange and

volcaniclastic Volcaniclastics are geologic materials composed of broken fragments (clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...

s. The rock units are firstly Chimei Volcanics Miocene

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 predomina ...

. Next is the Tuluanshan Formation, consisting of

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 co ...

, then Takangou Formation, consisting of sediments such as shale and sandstone that contain volcanic particles. The Lichi Formation consists of melange. It is made of mud containing blocks of other stone such as sandstone and

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is ...

. It is found on the southern half of the west side of the Coastal range. When this erodes,

badlands Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded."Badlands" in '' Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 2, p. 47. They are characterized by steep slopes, ...

are formed. Because it is a mixture of stone, the Lichi Formation is hard to date, but is likely to be from

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58conglomerate is found on Pinanshan Hill and along the Pinantachi stream north of Taitung (台東). The constituents are 5–15 cm cobbles erodes by freshwater from the Central Range. It formed somewhere from middle to late Pleistocene, and indicates the plate collision had taken place. The Milun Conglomerate is to the north of Hualien. This has also gone under the names of Beiron Conglomerate Formation and Milunpi Conglomerate. It is tilted at 30°. It is undated but is likely from Pleistocene.

Central Mountains strata

Shibachongxi Formation is from the Eocene consisting of slate and then beds of metamorphosed sandstone. The total thickness is up to 1000 m. Dajian Formation consists of sandstone from the upper Eocene, up to 2700 meters thick. Xichun Formation slate and

phyllite Phyllite ( ) is a type of foliation (geology), foliated metamorphic rock formed from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. I ...

is from the lower Oligocene. The thickness is from 0.6 to 3 km. Siling Formation coarse sandstone in thick beds is from the Oligocene. Shuichungliu Formation form the Oligocene contains argillaceous slate and graywacke. Bilushan Formation contains slate and phyllite from the Eocene. Lushan Formation from the Miocene contains shale slate and sandstone. Aodi Formation contemporary Sule Formation slate and sandstone from the later Miocene.

Western stratigraphic region

The west part of the island exposes deformed and metamorphosed

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

sediments, overlaid by

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

piedmont region in the flat plains on the west coast.

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

and Eocene deposits are not exposed on the surface, but are buried. They have been discovered by drilling. The Yunlin Formation is from the Cretaceous and only known from boreholes. The rocks are siltstone, basalt, shale and limestone. The Paleocene Wangong Formation consisting of

s, sandstone, shale and limestone is over 1046 meters thick. In the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

the Shuangji Formation formed mostly from volcanic particles in the form of tuff and tuffaceous sandstone. These beds are from 100 m to 3 km thick. In the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

the Wuzhishan Formation or Wuchihshan Formation (五指山組) formed thick beds of sandstone. The total thickness is 0.9 to 1.2 km. The Yeliu Group from the

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

is fine grained sandstone, with some beds of shale, basaltic tuff and three seams of

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 Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

. Possibly including Wushan Formation, Piling Shale, Peiliao Formation, Talu shale, Shihti Formation, Kuanyiongshan sandstone. The Ruifang Group contains beds of sandstone, siltstone, shale and six thin coal beds. These beds are 0.8 to 1.6 km thick. The Sangxia Group starts with medium grained sandstone, but in the upper layers increases shale. Eight thin coal seams are included. The total thickness of the deepest beds exceeds 5 km. This includes the Kueichulin Formation with the Yutengping Sandstone, Shihliufen Shale, Kuantaoshan Sandstone; the Nanchuang Formation including Shangfuchi Sandstone and Tungkeng Formation. The Jinshui Formation or Chinshui Formation from the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58mudstone 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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

and sandstone is between 80 and 400 m thick. The Zhuolan Formation or Cholan Formation (卓蘭層) starts in the Pliocene and extends into the first stage of the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. It consists of fine grained sandstone. This is 1.5 to 2.5 km thick. At the same time on the southern tip of the island, the Kending Formation or Kenting Formation (墾丁組) was formed consisting of mudstone with

melange. The ophiolite melange contains pebbles and blocks of Miocene age consisting of basic and ultrabasic rock from the ocean floor. The interpretation is that a wedge of seafloor was pushed above sea level, eroded and dropped fragments into the mud. The Toukoshan Formation (Toukeshan) (頭嵙山層) commenced with fine sandstone with thin beds of conglomerate, and continued into mainly conglomerate with sandstone beds. This was formed in stage 1 and 2 of the Pleistocene. It is from 0.4 to 3 km thick. The Szekou Formation is a light bluish gray siltstone, with shale and fine grained sandstone. The Maanshan Formation is very similar. It is overlain by Hengchun Limestone and may interfinger.

Western piedmont region

The Hengchun Limestone was formed after the Penglai movement in the third Pleistocene stage. Also at this time

laterite Laterite is a soil 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 intensive and prolo ...

(紅土) and gravel on river terraces was formed.

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

mud sand and coral form a wide belt on the west side of the island.

Volcanic rocks

The Tatun Volcanic Group is found on the northern tip of Taiwan. Chihsingshan is the highest point of the volcanoes at 1120 meters. The volcanoes have formed the rounded shape of the northern cape of Taiwan. The volcanic rock also occur on Huaping Isle, Mienhua Isle, Pengchia Isle and Huangwei Isle just to the north of Taiwan. The rocks are aluminium rich

and

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

. The rocks are poor in sodium and magnesium, but rich in iron, potassium, rubidium and strontium and strong in rare earth elements. The magma was derived by melting of the underthrust sea plate behind the Ryukyu Volcanic Arc during the

. The Caolingshan Basalt consists of olivine and pyroxene, with crystals of biotite and plagioclase. This is rich in K, Rb, Mg, Sr, Cr, and Ni, but poor in Na, Al, and Fe. Rare earth elements are strongly enriched. The magma was derived by deep mantle melting of the underthrust sea plate behind the Ryukyu Volcanic Arc during the Pleistocene. The volcanoes on Chilungshan, Penshan, Caoshan, Chilung Island (Keelung Islet) and Gueishan Island date from the Pleistocene period and later. The eruption were explosive tholeiitic andesite and

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 rhyolite. ...

. The main mineral is calcium rich

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

. The magma source is the western extremity of the Ryukyu Volcanic Arc formed when the

subducting Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second pla ...

was compressed below the edge of the Eurasian Plate at about 20 to 30 km deep. The magma was contaminated with continental crust material. Geochemistry of the rock shows that iron, aluminium, titanium, potassium, rubidium and strontium are enriched, but sodium, magnesium and nickel are impoverished. Alkaline volcanic rocks from north west Taiwan are found at the Shihmen Reservoir, Chiaopanshan, Taoyuan and Fuxing. The rocks are picrite, alkaline basalt and trachyandesite. The commons minerals are

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

, clinopyroxene and oxides of iron and titanium. The elements enriched are sodium and titanium, and magnesium and calcium are reduced. The rock dates from the Miocene. The magma was formed under tension conditions on the continental margin from deep down in the mantle. Volcanoes on the Coastal Range and Green Island erupted tholeiite andesite, and volcanic explosive fragments. The volcanoes erupted from the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Luzon Volcanic Arc The Luzon Volcanic Arc is a volcanic arc, chain of volcanoes in a north–south line across the Luzon Strait from Taiwan to Luzon. The name "Luzon Volcanic Arc" was first proposed by Carl Bowin et al. to describe a series of Miocene to recent vo ...

. Magma was formed from subducting

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 ultramaf ...

under compression about 25 km deep. The andesite rock contains some visible crystals of

pyroxene The pyroxenes (commonly abbreviated 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 ions of calcium (Ca), sodium (Na), iron ( ...

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

geochemistry Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...

of the rock shows it is enriched in

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

strontium Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...

and

rubidium Rubidium is a chemical element; it has Symbol (chemistry), symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have ...

and light rare earth elements. Chromium and nickel are depleted. The Chimei Volcanic Complex, near the Hsiukuluanchi River, has an age from 9 to 22.2 Ma. It is associated with copper porphyry mineralisation. It covers an area of 22 km². Pleistocene basalt and tholeiite is found in the

Penghu Islands The Penghu ( , Hokkien POJ: ''Phîⁿ-ô͘'' or ''Phêⁿ-ô͘'' ) or Pescadores Islands are an archipelago of 90 islands and islets in the Taiwan Strait, about west of the main island of Taiwan across the Penghu Channel, cove ...

. The lava erupted from fissures in a

flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...

. The rock is enriched in titanium and poor in aluminium, rubidium and strontium. The alkaline basalt contains olivine and analcite. The tholeiite contains plagioclase and pyroxene. The magma originated in the

upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (geology), crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle (Earth), lower man ...

under tension conditions on the continental margin.

Structures

*Hengchun Valley

syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed ...

under the Hengchun Valley *Hengchun Fault on east side of Hengchun Valley. It extends along the Pintung Valley as the Chaochow fault and Laonungchi fault. *Kenting Park

anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...

is overturned and folds Miocene rocks of the Changlo Formation, Lushan Formation to the north. Loshui Formation is on the sides of the anticline.

Tectonics

The Philippine Sea Plate is converging with the continent at 7 cm per year in the west north west direction. It has compressed Cenozoic sediments by around 200 km in the last 4 Ma. The piled up sediment is rising into mountains at the rate of 5 mm per year. Accretion of the material is caused by convergence and subduction of the Luzon arc and the Eurasian Plate. The major seismic faults in Taiwan correspond to the various suture zones between the various terranes. As a result, Taiwan has numerous

mud volcano A mud volcano or mud dome is a landform created by the eruption of mud or Slurry, slurries, water and gases. Several geological processes may cause the formation of mud volcanoes. Mud volcanoes are not true Igneous rock, igneous volcanoes as th ...

es and

hot spring A hot spring, hydrothermal spring, or geothermal spring is a Spring (hydrology), spring produced by the emergence of Geothermal activity, geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow ...

s. The suture zones involve arc to continent collision, making thrust melts and young mountain ranges. The mountain belt was formed roughly 6.5 Ma through oblique movement of the continental plate (Eurasian Plate) and the plate containing the volcanic arc (Luzon arc). The oblique movement allows for differing velocities of the subducting plate and deforms the crust at varying rates. Faults are produced through the release of tectonic stress by fracturing. Faults could form through compressional or tensional stresses. In the case of Tawian, faults are produced through compressional stresses and have brought about several major quakes throughout the history of the island, including the 1951 East Rift Valley earthquakes on the East Rift Valley (花東縱谷) and 1964 Baihe earthquake on the Chukou Fault. The 1946 Hsinhua earthquake ruptured the Hsinhua fault (新化斷層). The most lethal was 1935 Hsinchu-Taichung earthquake shifting on a fault at Emei Township,

Hsinchu County Hsinchu is a County (Taiwan), county in Regions of Taiwan, north-western Taiwan. The population of the county is mainly Hakka people, Hakka; with a Taiwanese aboriginal minority in the southeastern part of the county. Zhubei is the county seat ...

. The second deadliest was a 7.3 quake that ruptured the Chelongpu Fault (車籠埔斷層) on 21 September 1999, known as the " 921 earthquake". On 4 March 2010 at about 01:20 UTC, a magnitude 6.4 earthquake hit southern Taiwan. The seismic hazard map for Taiwan by the USGS shows 9/10 of the island as the highest rating (most hazardous).

Offshore

The offshore features include the Kaoping Slope extending off the southwest coast of Taiwan into the South China Sea. This is emerging from the sea over time to extend the island. The Hengchun Ridge extends south from the Hengchun Peninsula, and is the submarine part of the Central Range. The Southern Longitudinal Trough is the southern underwater extension of the Longitudinal Valley. The Huatang Ridge extends south off the coast from

. The Taitung Trough lies to the east behind the Luzon Arc. The Luzon Arc comes to the surface on the islands of Lüdao and Lanyu. A submarine canyon, the Taitung Canyon, cuts through the arc between the two islands linking the Taitung Trough to the Huatung Basin. The canyon cuts across the Huatung Basin bending to the north and reaching the Ryukyu Trench. A 5.5 magnitude earthquake struck at 08:00 GMT on 20 March 2011, near the canyon breaking segments C and D of the East Asia Crossing undersea cable. The Huatung Basin lies east of Taiwan south of the city of Hualien. It extends west till the Gagua Ridge about 110 km offshore. The Taiwan Banks are a shallow part of the main continental shelf off mainland China lying to the south and south west of

. The Taixinan Basin (台西南盆地) is located between Taiwan Banks and the Central Mountains. The Okinawa Trough, the

back-arc basin A back-arc basin is a type of geologic Structural basin, basin, found at some convergent boundary, convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found ...

behind the

Ryukyu Islands The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Geography of Taiwan, Taiwan: the Ryukyu Islands are divided into the Satsunan Islands (Ōsumi Islands, Ōsumi, Tokara Islands, Tokara and A ...

, shows up on the coastline as a bay between Dome Point north to Sanshokiaku (easternmost point of Taiwan) (24.6° to 25°N).

Geophysics

Taiwan has a very strong, positive Bouguer gravity anomaly in the Coastal Range, at over +4x10⁻⁴ ms⁻². A local low below -2x10⁻⁴ ms⁻² is on the western side centered near Zhoulan.Geology of China page 62 The gravity low is due to a mass deficit in the

Taiwan Strait The Taiwan Strait is a strait separating the island of Taiwan and the Asian continent. The strait is part of the South China Sea and connects to the East China Sea to the north. The narrowest part is wide. Names Former names of the Tai ...

which is a flexural basin. Positive magnetic variations are found in narrow strips, west-southwest oriented of the west coast, and east-northeast off the northern coast, and south-north offshore from the Coastal Range heading south. These are of the order of 200 nT. The Crustal thickness is around 30 km, with over 2 km of thickening under the Central Range, and thinning off the east coast. Taiwan is on the edge of the continental shelf, so the thickness of the crust is constant through the Taiwan Strait to the mainland. Heat flow is greatest to west of the Longitudinal Valley at rates exceeding 240 mWm⁻².

Hydrology

Beitou Thermal Valley warning sign 20050814

Many of the rocks in Taiwan have low pore space and have little ground water. There are several hot springs in Taiwan, with most around the northern volcanic region. The Chingshui geothermal region is named after the Cingshuei River 13 km south west of

Yilan Yilan may refer to: China * Yilan County, Heilongjiang (依兰县), county of central Heilongjiang province, People's Republic of China * Yilan Town, Heilongjiang (依兰镇), seat of Yilan County * Yilan, Jilin (依兰镇), town in Yanji Taiwan ...

. Rivers in Taiwan transport a large amount of sediment to the sea. The south end of the Longitudonal Valley discharges the Peinan River with 88,000,000 tons of sediment per year. East flowing rivers move 17, 15 31 and 22 megatons per year of sediment. The Cho Shiu shifts 54 MT per year. Rivers running south from the Central Range move over 100 MT of sediment per year.

Study

Mapping

The first

geological map A geological map or geologic map is a special-purpose map made to show various geological features. Rock (geology), Rock units or stratum, geologic strata are shown by color or symbols. Bed (geology), Bedding planes and structural features such ...

of Taiwan was made in 1898 by Y. Ishii titled ''A Map of Geology and Mineral Resources of the Island of Taiwan''. It was at a scale of 1:800,000 and showed six items in its legend. Japan needed oil and coal for the war against Russia in 1904, so study began on the coal fields in the north part of Taiwan, more detailed maps were made, and the next one was published in 1911 by Y. Deguchi and G. Hosoya at a scale of 1:300,000. A third map was produced in 1926 titled: ''Geological Map of Taiwan showing Mineral Distribution'' by Y. Ichikawa and H. Takahashi. It showed 19 rock units. A 1935 coloured map by Y. Ichikawa had a scale of 1:500,000. In 1953 the Geological Survey of Taiwan (台灣地質調查所) published a map compiled by L.S. Chang at a 1:300,000 scale. A 1974 map had two scales 1:250,000 and 1:500,000. A second edition was printed in 1986 along with notes.

References

External links

* {{Asia topic, Geology of