亚洲大地构造的演化

<正> 一、引言 最近作者用板块构造观点编制了一幅八百万分之一的亚洲大地构造图。从这幅图可以清楚地认识到亚洲地质构造比较复杂。它并非从古以来就是一个完整的大陆块,而是由于地壳长期以来分离聚合演化的结果。板块构造在地球上开始于什么时候,目前尚无定论。亚洲大地构造图的编制,主要是从显生宙初期开始的。

TECTONIC EVOLUTION OF ASIA

Recently the writers have compiled the "Tectonic Map of Asia" on a scale of 1:8000000. From this map, it can be clearly seen that the whole continent was not originally a single landmass, but a result of long time evolution from separated paleoplates. Based upon the important features of plate tectonics, Asia and its adjacent regions can be divided into 12 plates during the Phanerozoic, namely the Tarim-Sinokorean, South China-Southeast Asian, Siberian,Kazakhstanian, East European, Turkey-Central Iran-Gangdise, Arabian, African, Indian, Australian, Philippine Sea and Pacific Ocean plates.The above said plates did not coexist at the same time. They drifted variably from time to time. In the Early Paleozoic the Tarim-Sinokorean, Siberian, East European, Kazakhstanian and South China-Southeast Asian plates which made up the northern part of Asia, were separated from each other by oceans and were situated in the low latitude territories on both sides of the equator. The Gandwanaland on the other hand, remained integrated and was mainly located in the southern hemisphere. Owing to the convergent movement of the plates, the geosynclines (actually the geoclines) along the continental margins folded and/or subducted, forming the Early Paleozoic (Caledonian) fold belts. But the oceans among the plates were not yet closed. The convergent movement continued to the Late Paleozoic, bringing about the Late Paleozoic (Variscan) folding, subduction and finally collision of plates. These five plates joined together to form a combined land-mass which may be called the Paleo-Eurasia Plate. Nevertheless the South China-Southeast Asian Plate was not entirely welded together with the northern part of Asia.In the Early Mesozoic the Paleo-Eurasia Plate shifted dextrally and the South China-Southeast Asian plate moved northward to combine with the former along the suture of Kunlun and Western Qinling Mountains. This en- larged landmass may be called the MesoEurasia Plate. Meanwhile the Gand-wanaland began to disintegrate. A number of microcontinents separated from the northern part of Gandwanaland. They constituted the Turkey-Central Iran-Gangdise median plate. It welded together with the Meso-Eurasia Plate along the suture from the northern foot of Bolsoj Kavkaz-Kopet Dagh on the west and Hindu Kush, Bangong Lake up to Lancangjiang fracture on the east to form the Neo-Eurasia Plate. In the Late Mesozoic as well as in the Early Tertiary the Arabian Plate and the Indian Plate moved northward to collide with the Neo-Eurasia Plate. A well known suture line is found along Taurus-Zagros Mountains and Yarlung Zangbo River through to Bomi. The configuration of the modern Eurasia continent was then accomplished.Along the eastern margin of Asia from Kamchatka on the north through Japan southwestward as far as to Ryukyu Islands there existed some NE-trending subduction zones underthrusting to the continents since the Mesozoic, by which the two paired metamorphic belts in Japan were formed.The Longitudinal Valley in Taiwan Island represents a suture line between the Eurasia and Philippine Sea plates. The fan-shaped Hidaka folding in Hokaido, and the high pressure metamorphism in the inner belt and the high temperature metamorphism in the outer belt seem to reflect that an eastward subduction had happened along Sakhalin (Kuye) Island and the western side of Hidaka Mountains.The calcalkali igneous rocks are well developed in the eastern provinces of China. It is considered that there were some subduction lines in the sea region along the coast, and meanwhile on the land surface the Nadanhada fracture in eastern Heilongjiang Province and Changle-Zhaoan deep fault in Fujian Province may represent the westward subduction zones in the Late Mesozoic.The Indian Plate still moved northward in the Late Cenozoic. Thereby the Main Boundary Fault came to exist along the pidemont of Siwalik Range. This is a huge underthrust on the earth crust. It is called A-type subduction by some tectonic geologists.