Geology of Taiwan
Encyclopedia
Taiwan
is active geologically, showing plate boundary tectonics. The island formed at the junction of the Luzon Volcanic Arc
(呂宋島火山弧) and the Ryukyu Volcanic Arc (琉球火山弧). Subduction
changes direction at Taiwan. South of the island, the Philippine Sea Plate is subducting under the Sunda Plate
. To the north the Philippine Sea Plate is subducting under the Okinawa Plate
(沖繩板塊). The Philippines Plate is moving to the north east. The Manila Trench meets the southern tip of Taiwan. The North Luzon Trough extends into the island forming the inland Taitung Longitudinal Valley.
(海岸山脈) or Coastal Range terrane
belongs to the Luzon Volcanic Arc
(呂宋島火山弧), and is on the Philippine Sea Plate (菲律賓海板塊). West of this is the Longitudinal Valley or Huatung Valley
(花東縱谷), 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 metamorpism. The two metamorphic belts are possibly separated by a fault called Shoufeng fault, but this is unproven.
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
in age and consists of black schist and some greenschist
, glaucophane schist, and spotted slate. 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
, chlorite
, albite
, sphene, and graphite
.
The Changchun Schist being mostly Greenschist
is found on the western side and forms thick beds. It is found along with smaller amounts of chert, and black schist. The rock is foliated dark green rock containing chlorite
, epidote
, quartz, calcite, biotite, albite, and actinolite
. They are derived from mafic volcanic rocks. These rocks can host copper sulfide
ores.
Siliceous schists are coloured grey, they are metamorphosed sandstone, rich in quartz. Quartzite 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 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 derived from sedimentary rocks is coarde grained quartz, biotite, and albitic plagioclase. There is also orthogneiss derived from granite. This is light grey and contains sodic plagioclase, quartz, biotite, and muscovite. Within the gneiss there are pegmatite
dikes containing quartz, feldpsar and mica.
Other igneous rocks found in the old metamorphic belt are amphibolite
and dolerite dikes. Serpentinite
is found 5 km west of Fengtien (奉天). It contains exploited deposits of nephrite
, talc
and asbestos
. Wanjung Station (万荣) 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 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
around 40 Ma may be connected with some dolerite intrusions. The Penglai Orogeny started about 10 Ma and continues at the present time.
on the east coast from Taitung City
in the south to Hualien City in the north. The range is the continuation of the Luzon arc. The age is Neogene
and the rock consist of melange
and volcanicalstics. The rock units are firstly Chimei Volcanics Miocene andesite. Next is Tuluanshan Formation, consisting of tuff, 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. It is found on the southern half of the west side of the Coastal range. When this erodes, badlands
are formed. Because it is a mixture of stone, the Lichi Formation is hard to date, but is likely to be from Pliocene.
The Pinanshan conglomerate
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.
Dajian Formation consists of sandstone from the upper Eocene, up to 2700 meters thick.
Xichun Formation slate and phyllite
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.
sediments, overlaid by Quaternary
piedmont region in the flat plains on the west coast.
Cretaceous
, Paleocene
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 volcaniclastics, sandstone, shale and limestone is over 1046 meters thick.
In the Eocene
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 Wuzhishan Formation or Wuchihshan Formation (五指山組) formed thick beds of sandstone. The total thickness is 0.9 to 1.2 km.
Yeliu Group from Miocene
is fine grained sandstone, with some beds of shale, basaltic tuff and three seams of coal. Possibly including Wushan Formation, Piling Shale, Peiliao Formation, Talu shale, Shihti Formation, Kuanyiongshan sandstone.
Ruifang Group contains beds of sandstone, siltstone, shale and six thin coal beds. These beds are 0.8 to 1.6 km thick.
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 Kueichulin Formation with Yutengping Sandstone, Shihliufen Shale, Kuantaoshan Sandstone; the Nanchuang Formation including Shangfuchi Sandstone and Tungkeng Formation.
The Jinshui Formation or Chinshui Formation from the Pliocene
is mostly shale interbedded with some mudstone
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
. 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 墾丁组 was formed consisting of mudstone with ophiolite 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.
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.
(紅土) and gravel on river terraces was formed. Holocene
mud sand and coral form a wide belt on the west side of the island.
The Caolingshan Basalt consists of olivine and pyroxene, with crystals of biotite and plagioclase. This is rich in K Rb Mg Sr Cr 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
(基隆火山群), Penshan, Caoshan, Chilung Island (Keelung Islet) and Gueishan Island
date from the Pleistocene
period and later. The eruption were explosive tholeiitic andesite
and dacite
. The main mineral is calcium rich plagioclase
. The magma source is the western extremity of the Ryukyu Volcanic Arc (琉球火山弧) formed when the subducting Philippines Sea Plate 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 albite
, olivine
, 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 Lüdao erupted tholeiite
andesite
, and volcanic explosive fragments. The volcanoes erupted from the Pliocene
to Pleistocene
period. It is part of the Luzon Volcanic Arc
. Magma was formed from underthrusting oceanic crust
under compression about 25 km deep. The andesite rock contains some visible crystals of pyroxene
or amphibole
. The geochemistry
of the rock shows it is enriched in potassium
, strontium
and rubidium
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 Penhu Islands (澎湖群島). The lava erupted from fissures in a flood. 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 under tension conditions on the continental margin.
Taiwan is a major hazard area for earthquakes. It has mud volcano
es and hot spring
s.
Earthquakes included 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 921 earthquake
(921地震) was the second deadliest rupturing the Chelongpu Fault (車籠埔斷層). The most lethal one was 1935 Hsinchu-Taichung earthquake
shifting on a fault at Emei Township
(峨眉), Hsinchu County
.
The Henchung Ridge extends south from the Hengchun Peninsula (恆春半島), 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 Taitung City
. 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 Penghu Islands.
The Okinawa Trough
, the back-arc basin
behind Ryukyu Islands
, shows up on the coastline as a bay between Dome Point north to Sanshokiaku (easternmost point of Taiwan). (24.6° to 25°N)
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.
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
.
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.
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
is active geologically, showing plate boundary tectonics. The island formed at the junction of the Luzon Volcanic Arc
Luzon Volcanic Arc
The Luzon Volcanic Arc is a chain of volcanoes in a north south line across the Luzon Strait from Taiwan to Luzon. It is the northern extension of the Philippine Mobile Belt...
(呂宋島火山弧) and the Ryukyu Volcanic Arc (琉球火山弧). Subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
changes direction at Taiwan. South of the island, the Philippine Sea Plate is subducting under the Sunda Plate
Sunda Plate
The Sunda Plate is the tectonic plate on which the majority of Southeast Asia is located. It was formerly considered a part of the Eurasian Plate, but GPS measurements have confirmed its independent movement at 10 mm/yr eastward relative to Eurasia...
. To the north the Philippine Sea Plate is subducting under the Okinawa Plate
Okinawa Plate
The Okinawa Plate is a long narrow tectonic plate stretching from the northern end of Taiwan to the southern tip of the island of Kyūshū. To the east lies the Ryukyu Trench and the Pacific Plate. It is separated from the Yangtze Plate by a rift that forms the Okinawa Trough which is a Back arc...
(沖繩板塊). The Philippines Plate is moving to the north east. The Manila Trench meets the southern tip of Taiwan. The North Luzon Trough extends into the island forming the inland Taitung Longitudinal Valley.
Terranes
The Haian RangeHaian Range
The Hai-an Range , also known as the Coastal Range, is a mountain range lies on the east seashore of Taiwan and crossed the border of counties of Hualien and Taitung. Distinct from western lands of Taiwan, it is a part of Philippine Mobile Belt instead of the Yangtze Plate.The Huatung Valley, a...
(海岸山脈) or Coastal Range terrane
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
belongs to the Luzon Volcanic Arc
Luzon Volcanic Arc
The Luzon Volcanic Arc is a chain of volcanoes in a north south line across the Luzon Strait from Taiwan to Luzon. It is the northern extension of the Philippine Mobile Belt...
(呂宋島火山弧), and is on the Philippine Sea Plate (菲律賓海板塊). West of this is the Longitudinal Valley or Huatung Valley
Huatung Valley
Huatung Valley or Hualien-Taitung Valley , also known as East Rift Valley or the Longitudinal Valley, is a long and narrow valley located at the between Chungyang Range and Haian Range...
(花東縱谷), 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 metamorpism. 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 PermianPermian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
Period. They form a band of rock from Nan'ao
Nan-ao, Yilan
Nan-ao is a rural township in the southern part of Yilan County, Taiwan. It has a significant population of Atayal aborigines. The township was the site of the Sayun incident during Japanese rule, made famous through the movie Sayon's Bell....
in the north to inland of Jinfeng on the eastern flank of the Central Mountain Range
Central Mountain Range
The Central Mountain Range, also known as the Chungyang Range , is the principal range of mountains in Taiwan. It runs from the north of the island to the south.Due to this separation, connecting between the west and east is not so convenient...
. 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
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
in age and consists of black schist and some greenschist
Greenschist
Greenschist is a general field petrologic term applied to metamorphic or altered mafic volcanic rock. The term greenstone is sometimes used to refer to greenschist but can refer to other rock types too. The green is due to abundant green chlorite, actinolite and epidote minerals that dominate the...
, glaucophane schist, and spotted slate. 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
Mica
The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...
, chlorite
Chlorite
The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:...
, albite
Albite
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...
, sphene, and graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
.
The Changchun Schist being mostly Greenschist
Greenschist
Greenschist is a general field petrologic term applied to metamorphic or altered mafic volcanic rock. The term greenstone is sometimes used to refer to greenschist but can refer to other rock types too. The green is due to abundant green chlorite, actinolite and epidote minerals that dominate the...
is found on the western side and forms thick beds. It is found along with smaller amounts of chert, and black schist. The rock is foliated dark green rock containing chlorite
Chlorite
The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:...
, epidote
Epidote
Epidote is a calcium aluminium iron sorosilicate mineral, Ca2Al2O, crystallizing in the monoclinic system. Well-developed crystals are of frequent occurrence: they are commonly prismatic in habit, the direction of elongation being perpendicular to the single plane of symmetry. The faces are often...
, quartz, calcite, biotite, albite, and actinolite
Actinolite
Actinolite is an amphibole silicate mineral with the chemical formula .-Etymology:The name actinolite is derived from the Greek word aktis , meaning "beam" or "ray", because of the mineral's fibrous nature...
. They are derived from mafic volcanic rocks. These rocks can host copper sulfide
Copper sulfide
Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores....
ores.
Siliceous schists are coloured grey, they are metamorphosed sandstone, rich in quartz. Quartzite 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 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 derived from sedimentary rocks is coarde grained quartz, biotite, and albitic plagioclase. There is also orthogneiss derived from granite. This is light grey and contains sodic plagioclase, quartz, biotite, and muscovite. Within the gneiss there are pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
dikes containing quartz, feldpsar and mica.
Other igneous rocks found in the old metamorphic belt are amphibolite
Amphibolite
Amphibolite is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are...
and dolerite dikes. Serpentinite
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
is found 5 km west of Fengtien (奉天). It contains exploited deposits of nephrite
Nephrite
Nephrite is a variety of the calcium and magnesium-rich amphibole mineral actinolite . The chemical formula for nephrite is Ca25Si8O222. It is one of two different mineral species called jade. The other mineral species known as jade is jadeite, which is a variety of pyroxene...
, talc
Talc
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...
and asbestos
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...
. Wanjung Station (万荣) 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 outcrops.
Green serpentinite from near Yuli
Yuli, Hualien
Yu Li, Hualien , is a township located in central Huatung Valley, and also the southern administrative center of Hualien, Taiwan. It has a population of 27,500 inhabitants and 15 villages.- Transportation :...
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
South China Sea
The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...
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 RangeHaian Range
The Hai-an Range , also known as the Coastal Range, is a mountain range lies on the east seashore of Taiwan and crossed the border of counties of Hualien and Taitung. Distinct from western lands of Taiwan, it is a part of Philippine Mobile Belt instead of the Yangtze Plate.The Huatung Valley, a...
on the east coast from Taitung City
Taitung City
Taitung City is the county seat of Taitung County, Taiwan. It lies on the southeast coast of Taiwan facing the Pacific Ocean.The city is served by Taitung Airport. Taitung is a gateway to Green Island and Orchid Island, both of which are very popular among Taiwanese tourists.-History:Taitung...
in the south to Hualien City in the north. The range is the continuation of the Luzon arc. The age is Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
and the rock consist of melange
Melange
Melange also called the "spice" is the name of the fictional drug central to the Dune series of science fiction novels by Frank Herbert, and derivative works....
and volcanicalstics. The rock units are firstly Chimei Volcanics Miocene andesite. Next is Tuluanshan Formation, consisting of tuff, 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. It is found on the southern half of the west side of the Coastal range. When this erodes, badlands
Badlands
A badlands is a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded by wind and water. It can resemble malpaís, a terrain of volcanic rock. Canyons, ravines, gullies, hoodoos and other such geological forms are common in badlands. They are often...
are formed. Because it is a mixture of stone, the Lichi Formation is hard to date, but is likely to be from Pliocene.
The Pinanshan conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
is found on Pinanshan Hill and along the Pinantachi stream north of Taitung
Taitung City
Taitung City is the county seat of Taitung County, Taiwan. It lies on the southeast coast of Taiwan facing the Pacific Ocean.The city is served by Taitung Airport. Taitung is a gateway to Green Island and Orchid Island, both of which are very popular among Taiwanese tourists.-History: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
Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradation in the degree of metamorphism between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky, sometimes golden sheen to the...
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 CenozoicCenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
sediments, overlaid by Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
piedmont region in the flat plains on the west coast.
Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
, Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
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 volcaniclastics, sandstone, shale and limestone is over 1046 meters thick.
In the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
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
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
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.
Yeliu Group from Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
is fine grained sandstone, with some beds of shale, basaltic tuff and three seams of coal. Possibly including Wushan Formation, Piling Shale, Peiliao Formation, Talu shale, Shihti Formation, Kuanyiongshan sandstone.
Ruifang Group contains beds of sandstone, siltstone, shale and six thin coal beds. These beds are 0.8 to 1.6 km thick.
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 Kueichulin Formation with Yutengping Sandstone, Shihliufen Shale, Kuantaoshan Sandstone; the Nanchuang Formation including Shangfuchi Sandstone and Tungkeng Formation.
The Jinshui Formation or Chinshui Formation from the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
is mostly shale interbedded with some mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
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
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
. 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 墾丁组 was formed consisting of mudstone with ophiolite melange
Melange
Melange also called the "spice" is the name of the fictional drug central to the Dune series of science fiction novels by Frank Herbert, and derivative works....
. 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.
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 lateriteLaterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
(紅土) and gravel on river terraces was formed. Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
mud sand and coral form a wide belt on the west side of the island.
Volcanic rocks
The Tatun mountain volcanics are 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 andesite, tuff and breccia. 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 Pleistocene.The Caolingshan Basalt consists of olivine and pyroxene, with crystals of biotite and plagioclase. This is rich in K Rb Mg Sr Cr 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
Chilung Volcano Group
Chilung Volcanoes , a group of volcanoes located at northern Taiwan, is just lies on the east of Taipei and Keelung , and adjoins the northern coast of the Taiwan island. It comprises the largest gold-copper deposits of Taiwan....
(基隆火山群), Penshan, Caoshan, Chilung Island (Keelung Islet) and Gueishan Island
Gueishan Island
Guishan Island or Steep Island or Turtle Island , also known as Kueishan Island, is an island in the Pacific Ocean currently administered by Yilan County, Taiwan and located east of port of Gengfang Fishery Harbor. The island is the top of an andesite stratovolcano which rises from the seafloor...
date from the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
period and later. The eruption were explosive tholeiitic andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
and dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
. The main mineral is calcium rich plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
. The magma source is the western extremity of the Ryukyu Volcanic Arc (琉球火山弧) formed when the subducting Philippines Sea Plate 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
Trachyandesite
Trachyandesite is an extrusive igneous rock. It has little or no free quartz, but is dominated by alkali feldspar and sodic plagioclase along with one or more of the following mafic minerals: amphibole, biotite or pyroxene...
. The commons minerals are albite
Albite
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...
, olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
, 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 Lüdao erupted tholeiite
Tholeiite
The tholeiitic magma series is one of two main magma series in igneous rocks, the other magma series being the calc–alkaline. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...
andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
, and volcanic explosive fragments. The volcanoes erupted from the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
to Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
period. It is part of the Luzon Volcanic Arc
Luzon Volcanic Arc
The Luzon Volcanic Arc is a chain of volcanoes in a north south line across the Luzon Strait from Taiwan to Luzon. It is the northern extension of the Philippine Mobile Belt...
. Magma was formed from underthrusting oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
under compression about 25 km deep. The andesite rock contains some visible crystals of pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
or amphibole
Amphibole
Amphibole is the name of an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.-Mineralogy:...
. The geochemistry
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
of the rock shows it is enriched in potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
and rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
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 Penhu Islands (澎湖群島). The lava erupted from fissures in a flood. The rock is enriched in titanium and poor in aluminium, rubidium and strontium. The alkaline basalt contains olivine and analcite
Analcite
Analcime or analcite is a white, grey, or colourless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi2O6·H2O. Minor amounts of potassium and calcium substitute for sodium...
. The tholeiite contains plagioclase and pyroxene. The magma originated in the upper mantle under tension conditions on the continental margin.
Structures
- Hengchun Valley synclineSynclineIn structural geology, a syncline is a fold, with younger layers closer to the center of the structure. A synclinorium is a large syncline with superimposed smaller folds. Synclines are typically a downward fold, termed a synformal syncline In structural geology, a syncline is a fold, with younger...
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 anticlineAnticlineIn structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
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 Philippines 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.Taiwan is a major hazard area for earthquakes. It has mud volcano
Mud volcano
The term mud volcano or mud dome are used to refer to formations created by geo-excreted liquids and gases, although there are several different processes which may cause such activity. Hot water mixes with mud and surface deposits. Mud volcanoes are associated with subduction zones and about 700...
es and hot spring
Hot spring
A hot spring is a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal hot springs in many locations all over the crust of the earth.-Definitions:...
s.
Earthquakes included the 1951 East Rift Valley earthquakes
1951 East Rift Valley earthquakes
The 1951 East Rift Valley earthquakes were a series of 735 earthquakes which struck eastern Taiwan from October 22, 1951 to December 5, 1951, four of which registered over 7 on the Richter Scale, the largest of those being two magnitude 7.3 quakes on October 22 and November 25...
on the East Rift Valley (花東縱谷) and 1964 Baihe earthquake
1964 Baihe earthquake
The 1964 Baihe earthquake , also known as the Great Baihe earthquake, was a deadly earthquake measured at 6.3 ML, occurred at 20:04 CST on 18 January 1964 in Baihe Township of Tainan County , Taiwan. The hypocenter of the earthquake was 20 kilometers deep...
on the Chukou Fault. The 1946 Hsinhua earthquake
1946 Hsinhua earthquake
The 1946 Hsinhua earthquake , also referred to as the 1946 Tainan earthquake was a magnitude 6.1 earthquake which hit Tainan County , Taiwan, on December 5, 1946 at 06:47...
ruptured the Hsinhua fault (新化斷層). The 921 earthquake
921 earthquake
The 921 earthquake , also known as Jiji earthquake , was a 7.3 Ms or 7.6 Mw earthquake which occurred at 1:47:12 am local time in Jiji , Nantou County, Taiwan. 2,415 people were killed, 11,305 injured, and NT$300 billion worth of damage was done...
(921地震) was the second deadliest rupturing the Chelongpu Fault (車籠埔斷層). The most lethal one was 1935 Hsinchu-Taichung earthquake
1935 Hsinchu-Taichung earthquake
The 1935 Hsinchu-Taichung earthquake was a magnitude 7.1 earthquake which occurred on April 21, 1935, with its epicentre in Sanyi , Miaoli County, Taiwan. It was the deadliest earthquake in Taiwan's recorded history, claiming 3,276 lives and causing extensive damage...
shifting on a fault at Emei Township
Emei, Hsinchu
Emei is a town in Hsinchu County in northern Taiwan. It had an estimated population of 6,127 as of 2007....
(峨眉), Hsinchu County
Hsinchu County
Hsinchu County is a county in north-western Taiwan. The population of the county is mainly Hakka; there is a Taiwanese aboriginal minority in the southeastern part of the county. Zhubei is the capital of Hsinchu, where the government office and county office is located...
.
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 Henchung Ridge extends south from the Hengchun Peninsula (恆春半島), and is the submarine part of the Central Range. The Southern Longitudinal Trough is the southern underwater extension of the Longitudinal Valley
Huatung Valley
Huatung Valley or Hualien-Taitung Valley , also known as East Rift Valley or the Longitudinal Valley, is a long and narrow valley located at the between Chungyang Range and Haian Range...
. The Huatang Ridge extends south off the coast from Taitung City
Taitung City
Taitung City is the county seat of Taitung County, Taiwan. It lies on the southeast coast of Taiwan facing the Pacific Ocean.The city is served by Taitung Airport. Taitung is a gateway to Green Island and Orchid Island, both of which are very popular among Taiwanese tourists.-History:Taitung...
. 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
Orchid Island
Orchid Island is a 45-km² volcanic island off the southeastern coast of Taiwan island and separated from the Batanes of the Philippines by the Bashi Channel of the Luzon Strait. It is governed as Lanyu Township of Taitung County...
. 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
Ryukyu Trench
The Ryukyu Trench is a 2,250 kilometer long oceanic trench along the southeastern edge of Japan's Ryukyu Islands in the Philippine Sea in the Pacific Ocean. It is located between northeastern Taiwan and southern Japan...
. 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 Penghu Islands.
The Okinawa Trough
Okinawa Trough
The is a seabed feature of the East China Sea. It is an active, initial back-arc rifting basin which has formed behind the Ryukyu arc-trench system in the West Pacific. It developed where the Philippine Sea Plate is subducting under the Eurasia Plate....
, the back-arc basin
Back-arc basin
Back-arc basins are geologic features, submarine basins associated with island arcs and subduction zones.They are found at some convergent plate boundaries, presently concentrated in the Western Pacific ocean. Most of them result from tensional forces caused by oceanic trench rollback and the...
behind Ryukyu Islands
Ryukyu Islands
The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...
, 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 just about the strongest positive Bouguer gravity anomoly in China 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 Cholan. The gravity low is due to a mass deficit in the Taiwan Strait 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
Taiwan Strait
The Taiwan Strait or Formosa Strait, formerly known as the Black Ditch, is a 180-km-wide strait separating Mainland China and Taiwan. The strait is part of the South China Sea and connects to East China Sea to the northeast...
to the mainland.
Heat flow is greatest to west of the Longitudinal Valley at rates exceeding 240 mWm−2.
Hydrology
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
Yilan may refer to:*Yilan County, Heilongjiang , People's Republic of China*Yılankale, a crusader castle in Turkey*Ye Yilan , Taiwanese writer*Yilan, Yanji , town in Jilin, PRC...
.
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.