东亚大地构造发展的重要转折

GEOTECTONIC TRANSITION FROM PALEOASIAN SYSTEM AND PALEOTETHYAN SYSTEM TO PALEOPACIFIC ACTIVE CONTINENTAL MARGIN IN EASTERN ASIA

本文根据现实主义原则和现代地质学理论，分析综合了东亚构造地质、古地磁、古生物地理、地质年代学等方面的一些最新研究成果，提出东亚古亚洲洋构造系和古特堤斯构造系向环太平洋主动陆缘的转变最终出现在中侏罗世，著名的燕山运动正是这一重要构造转折的产物。

In this paper, we discuss the geotectonic transition from Paleoasian system and Paleotethyan system to Paleopacific active continental margin of eastern Asia. For the past decade, most of authors have considered that this vital tectonic turnaround in eastern China and its adjacent areas appeared in Triassic (Indosinian). Having analysed and synthesized the recent data of structural geology, tectonics, paleobiogeography, paleomagnetism, and so on from the viewpoints of actualism and the complex orogenic process from initial collision to eventual consolidation, we propose that it may have occurred in middle Jurassic. It was this important tectonic turnaround that resulted in the well-known 'Yanshanian Movement' throughout eastern China and its adjacent areas.The consolidation of the Siberian Plate, the North China Plate and the Yangtze Plate was the basis of formation of Paleopacific active continental margin of eastern Asia.In Central Asian-Mongolian Orogen, huge nappe strutures, with 1500km in length and 170-200km in nappe displacement distance, developed during late Triassic-early Jurassic probably to middle Jurassic, almost at the same time as thrusts and nappes previously recorded in and around the regions. Mongolia-Okhotsk Sea eventurally disappeared in early-middle Jurassic. SystematiC and reliable paleomagnetic data from the Ordos Basin, North China, the other paleomagnetic data published and the revised and synthetic apparent polar wandering path of the Eurasian Plate lay con6traints on the collision and consolidation of the three main plates. Absence of obvious postearly Cretaceous deformation in those regions and paleobiogeographic study of China indicate the consolidatin of the Siberian Plate and the North China Plate in early Cretaceous, with the North China Plate unified the Yangtze Plate in middle-ate Jurassic.Along the northern margin of the North China Plate, a Triassic alkaline syenite belt distributes in Yanshan and Liaohe regions with EW-ENE direction The cover sequences of Yanshan and Liaohg regions folded and thrusted during Triassic to middle Jurassic. Those Triassic alkaline syenite belt and folds extend into northwestern Korea, the latter called 'the Liaodung direction'. Therefore, Indosinian Movement and early Yanshanian Movement of Yanshan region and the Songnim Disturbance of North Korea were the effects of the Central Asian-Mongolian Orogen rather than Paleopacific active continental margin of eastern Aisa.Subduction of Paleopacific oceanic crust beneath eastern Aisan continental margin commenced around griddle Jurassic. Trench turbidite wedges represent their subduction age of subduction complexes that the trench turbidite wedges consist partly of.Most of the trench turbidite wedges in Jurassic subduction complexes of eastern Aisa range in age from middle Jurassic to earliest Cretaceous. They distribute from Nadanhada, through Sikhote-Aim, Japan, Ryukyu, to Taiwan. Magmatic belts of the south-eastern coast of China and Japan developed during late Jurassic-early Cretaceous, may be slightly younger owiog to most of Rb-Sr and K-Ar age. The Juassic subduction complexes and the magmatic belts constituted the unitary trench-arc system of eastern Asian continental margin during middle Jurassic-early Cretaceous. There was no such a trench-arc system in eastern Asia until middle Jurassic. Permian subduction complexes in Japan can be considered as composite terranes or the other cases.