Geology of Taiwan

Source: Wikipedia, the free encyclopedia.
Taiwan lies on the western edge of the Philippine Plate.
3D block diagram showing plate tectonic setting of Taiwan

The

island of Taiwan was formed approximately 4 to 5 million years ago at a convergent boundary between the Philippine Sea Plate 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.[1][2]
Most of the island comprises a huge fault block tilted to the west.[3]

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 Philippine Sea Plate on the east and south, and the Sunda Plate to the southwest. Subduction changes direction at Taiwan. The upper part of the crust on the island is primarily made up of a series of terranes, mostly old island arcs 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.[4]

South of Taiwan, the Sunda Plate is subducting under the Philippine Sea Plate, forming the

Taitung Longitudinal Valley of Taiwan respectively.[5]

From the northeast of Taiwan and continuing eastwards in the

Ryukyu Volcanic Arc
.

External image
image icon Geology Map of Taiwan
Taiwan seismicity, showing both magnitude and depth of earthquakes.

Terranes

Hai'an Range

The

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.[6]

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.[7]

Central Mountains

Central Mountain Range

The oldest exposed rocks are heavily metamorphosed and found in the Central Mountains.

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.[9]
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

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.[10]

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.[10]

The Kainangan Gneiss or Kanagan Formation occurs in several elongated bodies. The gneiss derived from sedimentary rocks contains coarse 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, feldspar and mica.[10]

Other igneous rocks found in the old metamorphic belt are

ultramafic outcrops.[10]

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).[10]

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.[11]

Eastern stratigraphic region

The most recently added part of the island is the

volcaniclastics. The rock units are firstly Chimei Volcanics Miocene andesite. Next is the 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.[12]

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.[12]

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.[12]

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.[8]

Dajian Formation consists of sandstone from the upper Eocene, up to 2700 meters thick.[8]

Xichun Formation slate and phyllite is from the lower Oligocene. The thickness is from 0.6 to 3 km.[8]

Siling Formation coarse sandstone in thick beds is from the Oligocene.[8]

Shuichungliu Formation form the Oligocene contains

graywacke.[8]

Bilushan Formation contains slate and phyllite from the Eocene.[8]

Lushan Formation from the Miocene contains shale slate and sandstone.[8]

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 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.

The Yeliu Group from the Miocene is fine grained sandstone, with some beds of shale, basaltic tuff and three seams of coal.[13] Possibly including Wushan Formation, Piling Shale, Peiliao Formation, Talu shale, Shihti Formation, Kuanyiongshan sandstone.[14]

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.[14]

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 (墾丁組) was formed consisting of mudstone with ophiolite melange.[15] 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.[16]

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.[15]

Western piedmont region

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

river terraces was formed. Holocene mud sand and coral form a wide belt on the west side of the island.[17]

Volcanic rocks

External image
image icon Volcanic Distribution Map

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.[8]

The

subducting Philippine 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.[8]

Alkaline volcanic rocks from north west Taiwan are found at the

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.[8]

Volcanoes on the Coastal Range and

copper porphyry mineralisation. It covers an area of 22 km2.[19]

Pleistocene basalt and tholeiite is found in the

upper mantle under tension conditions on the continental margin.[8]

Structures

  • Hengchun Valley syncline under the Hengchun Valley[15]
  • Hengchun Fault on east side of Hengchun Valley. It extends along the Pintung Valley as the Chaochow fault and Laonungchi fault.[15]
  • Kenting Park anticline is overturned and folds Miocene rocks of the Changlo Formation, Lushan Formation to the north. Loshui Formation is on the sides of the anticline.[15]

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.[8]

The major seismic faults in Taiwan correspond to the various suture zones between the various terranes. As a result, Taiwan has numerous

seismic hazard map for Taiwan by the USGS shows 9/10 of the island as the highest rating (most hazardous).[21]

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. [6]

The Hengchun Ridge extends south from 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.[6]

The Taiwan Banks are a shallow part of the main continental shelf off mainland China lying to the south and south west of

(台西南盆地) is located between Taiwan Banks and the Central Mountains.

The Okinawa Trough, the back-arc basin behind the 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).[6]

Geophysics

Taiwan has a very strong, positive

Zhoulan.[25] The gravity low is due to a mass deficit in the Taiwan Strait which is a flexural basin.[14]

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.[26]

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.[25]

Heat flow is greatest to west of the Longitudinal Valley at rates exceeding 240 mWm−2.

Hydrology

Beitou hot spring valley

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.[27]

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.[28]

Study

Mapping

The first

geological map 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.[29] 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.[29] A third map was produced in 1926 titled: Geological Map of Taiwan showing Mineral Distribution by Y. Ichikawa and H. Takahashi.[29] It showed 19 rock units.[29] A 1935 coloured map by Y. Ichikawa had a scale of 1:500,000.[29] 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.[29] A second edition was printed in 1986 along with notes.[29]

References

  1. ^ "The Geology of Taiwan". Department of Geology, National Taiwan Normal University. Archived from the original on 22 February 2008.
  2. ^ "Geology of Taiwan". Department of Geology, University of Arizona. Archived from the original on 2017-04-13. Retrieved 2012-05-06.
  3. .
  4. ^ "Geology of Taiwan — University of Arizona". Geo.arizona.edu. Archived from the original on 13 April 2017. Retrieved 1 August 2010.
  5. p84–86
  6. ^ a b c d e Megan Anderson (5 March 2001). "Introduction to Geologic Features". Taiwan: An Active Continental Subduction Zone. Archived from the original on 15 June 2017. Retrieved 20 March 2011.
  7. ^ "Metamorphc Belts". Archived from the original on 2010-12-15.
  8. ^ .
  9. ^ "Eastern Central Range Introduction". Archived from the original on 2011-05-24.
  10. ^ a b c d e f "Eastern Central Range Occurrence and Lithology of Metamorphic Rocks". Archived from the original on 2010-12-15.
  11. ^ "Eastern Central Range Radiometric Ages". Archived from the original on 2010-12-15.
  12. ^ a b c Central Geological Survey MOEI. "Eastern Coastal Range Stratigraphy and Lithology". Archived from the original on 2011-09-27.
  13. ^ "Tertiary in Petroliferous Regions of China" (PDF).
  14. ^ .
  15. ^ a b c d e "Geology of the Hungchun Peninsula". Archived from the original on 2011-07-24.
  16. ^ Benjamin M. Page; Ching-Ying Lan (May 1983). "The Kenting Melange and its Record of Tectonic Events" (PDF). Memoir of the Geological Society of China (5): 227–248. Archived from the original (PDF) on 2016-03-05.
  17. ^ Song Zhi-chen; Huang Fei (February 2004). "Cretaceous and Tertiary Palynofloras in Taiwan Area and its Correlation with those in Neighbouring Coastal Regions of Mainland China". Journal of Tropical Oceanography.
  18. ^ "Geographic Setting". Geology of Taiwan. Central Geological Survey. Archived from the original on 24 May 2011.
  19. ^ "構造模型實驗室 盧佳遇老師 - Eastern Coastal Range". Archived from the original on 2011-07-24. Retrieved 2011-03-21.
  20. ^ Theodorou, Christine; Lee, Andrew (3 March 2010). "6.4-magnitude quake hits southern Taiwan". CNN.com. Archived from the original on 5 March 2010. Retrieved 4 March 2010.
  21. ^ "USGS seismic hazard map of Eastern Asia". Seismo.ethz.ch. Archived from the original on 2000-03-03. Retrieved 2011-05-30.
  22. S2CID 54689775
    .
  23. (PDF) on 2011-08-30.
  24. ^ "Magnitude 5.5 - TAIWAN REGION". Archived from the original on 2011-03-24. Retrieved 2017-08-28.
  25. ^ a b Geology of China page 62
  26. ^ Geology of China page 66
  27. ^ K. C. Fan; et al. (30 January 2006). "Evaluation of Natural Recharge of Chingshui Geothermal Reservoir in Taiwan" (PDF). Archived (PDF) from the original on 11 March 2016. Retrieved 31 March 2011.
  28. ^ "Home - Springer". Springerimages.com. Archived from the original on 13 March 2012. Retrieved 4 November 2018.
  29. ^ a b c d e f g "Earlier Geologic Maps Of Taiwan". Archived from the original on 2011-05-24.

External links

  • Chao-Hsia Chen; Hsin-Chang HoKai-Shuan Shei; et al. (2000). "Geologic Map of Taiwan". Central Geological Survey, Ministry of Economic Affairs. Archived from the original on 2011-08-15. Retrieved 2011-03-29.