昆仑多岛弧盆系及泛华夏大陆的增生

MULTI-ARC-BASIN SYSTEM OF KUNLUN OROGENIC BELT AND THE PAN-CATHAYSIAN CONTINENTAL ACCRETION

自从Rodinia超大陆在晚元古代解体之后,冈瓦纳大陆群与泛华夏大陆群间从晚元古代至中生代始终存在一大洋-特提斯洋。从早古生代至中生代,特提斯洋分三个阶段向泛华夏陆块群俯冲,形成了弧后扩张、弧陆碰撞和弧前增生。弧后盆地扩张到达小洋盆,出现蛇绿混杂岩。由于早期大陆边缘已向南发生了增生,继后的弧后扩张和前锋弧的位置也就相应地向南迁移了。因而蛇绿岩带、岩浆岩带会出现多条,且从北向南时代有从老变新的趋势。由于陆缘向南裂离,并到达高纬度位置,或者如洋岛的生成,随着洋壳的消减速、俯冲,高纬度的沉积体向低纬度的不断增生,这样就出现了生物的冷暖型混生。且从泛华夏陆块群或从冈瓦纳大陆群裂离的块体不能越过大洋中脊拼合在另一大陆块体上。因此,泛华夏大陆的西南缘-昆仑带只是在弧后海底扩张、弧-弧碰撞、弧-陆碰撞的多岛弧造山作用、向南不断增生过程中形成的。

All the time there is a ocean between Gondwana and pan Cathaysian continental groups from the Neoproterozoic to the Mesozoic. The continental margin is spilt and arc basin system is formed during northward subduction of the original Tethys. From early Paleozoic to the Mesozoic there are three subductions, which form back arc expansion, arc continent collision and fore arc accretion. The mix living biology presents in eary Ordovician, early Permian and the Mesozoic. The small ocean basin is formed and the ophiolite appear when back arc basin expands. With early fore arc accreted southward, the back arc expanding and leading arc are move southward. So there are many ophiolites and magma belts, whose ages are very younger from north to south. The broad outline of this evolutionary scheme may be as follows.The proto Tethys from the Early Sinian to the Silurian, which is characterized by the evolution of the frontal arc and the Early Palaeozoic arc basin system in the pan Cathaysian continental group. The palaeo Tethys Ocean from the Devonian to Middle Triassic, which is characterized by the evolution of the Late Palaeozoic Mesozoic arc basin on the southwestern margin of the pan Cathaysian continental group.In a word, the southwest edge of the pan Cathysia is formed by accretion southward when back arc expands, arc arc collids, arc continent collids and orogeny takes place.