Friday, December 10, 2021

Geology | Dec. 11, 2021

 Convergent boundary

​Geology of Taiwan

The island of Taiwan 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 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.[1]

South of Taiwan, the Philippine Sea Plate is subducting under the Sunda Plate, forming the Luzon Volcanic Arc (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.[2]
To the northeast, the Philippine Sea Plate is subducting under the Okinawa Plate, forming the Ryukyu Volcanic Arc.

​台灣地質
臺灣位於菲律賓海板塊歐亞板塊的聚合邊界,為一個造山作用活躍的活動構造區,根據GPS觀測資料,菲律賓海板塊以每年8.2公分的移動速度向西北移動[1]。菲律賓海板塊的隱沒方向在臺灣改變,在臺灣南方,歐亞板塊朝東隱沒到菲律賓海板塊之下,形成馬尼拉海溝及其東側的呂宋火山島弧,到了臺灣北方,菲律賓海板塊則是朝北隱沒到歐亞板塊之下,造成琉球海溝及其北側的琉球火山島弧沖繩海槽[2]

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 plane where many earthquakes occur, called the Wadati–Benioff zone.[1] These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.
Plate tectonics is driven by convection cells in the mantle. Convection cells are the result of heat generated by radioactive decay of elements in the mantle escaping to the surface and the return of cool materials from the surface to the mantle.[2] These convection cells bring hot mantle material to the surface along spreading centers creating new crust. As this new crust is pushed away from the spreading center by the formation of newer crust, it cools, thins, and becomes denser. Subduction begins when this dense crust converges with less dense crust. The force of gravity helps drive the subducting slab into the mantle.[3] As the relatively cool subducting slab sinks deeper into the mantle, it is heated, causing hydrous minerals to break down. This releases water into the hotter asthenosphere, which leads to partial melting of asthenosphere and volcanism. Both dehydration and partial melting occurs along the 1,000 °C (1,830 °F) isotherm, generally at depths of 65 to 130 km (40 to 81 mi).[4][5]

Some lithospheric plates consist of both continental and oceanic lithosphere. In some instances, initial convergence with another plate will destroy oceanic lithosphere, leading to convergence of two continental plates. Neither continental plate will subduct. It is likely that the plate may break along the boundary of continental and oceanic crust. Seismic tomography reveals pieces of lithosphere that have broken off during convergence.[citation needed]

聚合性板塊邊緣Convergent plate boundary / Destructive plate boundary,又譯大陸匯聚帶聚合性板塊邊界破壞性板塊邊界),顧名思義,是指邊界兩旁板塊相移近之處。其動力源自軟流圈中下沈的熔岩對流,乃三種主要板塊邊界之一。由於板塊相撞時產生巨大擠壓力和摩擦力,並形成俯衝帶,產生大量熔岩,故容易觸發地震火山爆發海嘯自然災害。與此同時,亦造出褶曲山脈海溝火山火山島弧等自然地貌。


Picture

Pingxi District (Chinese平溪區pinyinPíngxī QūWade–GilesP'ing2-hsi1 Ch'ü1Pe̍h-ōe-jīPêng-khoe-khu, Pêng-khe-khu; also spelled Pinghsi), is a rural district in New TaipeiTaiwan. The source of the Keelung River is in Jingtong, which is inside Pingxi District. It was an important coal mining town in the early 20th century. Its population of 4,872 as of January 2016 is the smallest among the districts of New Taipei City.   more info.


平溪區 - 维基百科,自由的百科全书 (wikipedia.org)臺灣話Pîng-khoe-khu)位於中華民國新北市東部,東北鄰瑞芳區、東南鄰雙溪區、南鄰坪林區、西南鄰石碇區、西北鄰汐止區基隆市暖暖區。平溪區境內多山,屬於伏獅山區,具有煤炭礦層。由於礦產業沒落導致人口嚴重流失,目前人口約於四千多人,為新北市人口最少的行政區,與人口最多的板橋區差距125倍。也是全國老年人口最高的一個行政區,占全區人口30%以上。每年元宵節放天燈是平溪最為人所熟知的重要節慶[1]。    有關更多

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