IMPLICATION OF THE TECTONIC EVOLUTION OF PALEO-ASIAN OCEAN

The paleo-Asian Ocean was not a simple ocean basin between Siberian Platform and North China Platform but an integration of complex activities(including long-distance migration) by multiple ocean basins of varied sizes opening and closing at different times and in different regions. The northern ocean basin originated from the Cambrian ocean basin formed by the disintegration of Gondwana archicontinent during late Neoproterozoic-early Cambrian(573-522 Ma), with the fragments of disintegrated Gondwana archicontinent, Cambrian oceanic crust, and continental margin transitional crust collided with each other and combined to form the original Central Asia-Mongolian archicontinent in late Cambrian-early Ordovician(510-480 Ma). The archicontinent then formed an active continental margin in Ordovician and a stable continent in Silurian in the south, and disintegrated in Early Devonian, with the fragments moving northward along the sinistral fault in the newly-formed Devonian ocean and reaching the southern margin of Siberian platform in late Late Devonian to form the present Central Asian-Mongolian archicontinent. The Late Carboniferous (318-316 Ma) and Early Permian (295-285 Ma) rifting magmatism occurred in the present Central Asian-Mongolian archicontinent in Late Paleozoic, forming bimodal volcanic rocks and alkaline granites. Mongolia-Okhotsk belt, as the Devonian ocean basin between Siberian archicontinent and Central Asia-Mongolian archicontinent connecting the paleo-Pacific Ocean eastward, developed until the Middle-Late Jurassic and ended at the same time as the ocean, of which the oceanic crust moved to the margin of Siberian platform and subducted under the platform, forming the wide epicontinental magmatic belt on the southern margin of platform, very active during Middle Devonian-Late Jurassic. The southern ocean basin of paleo-Asian Ocean began in Late Cambrian when the North China craton split from Gondwana land and formed the Late Cambrian-Early Ordovician passive continental margin and Middle Ordovician-Early Silurian trench-arc-basin system in the northern margin. The distribution of Silurian brachiopod biota indicates that the northern margin of North China Platform is related to the northern margin of Tarim Platform, western Sichuan, Yunnan, and eastern Australia, but not to the above northern ocean basin of paleo-Asian Ocean, with Songnen-Turan block between the two ocean basins. The arc-continent collision occurred in the northern North China Platform during Late Silurian-Early Devonian, forming continental volcanic belt in the south margin of Songnen block in Devonian. With the collision between North China Platform and Songnen block during Late Permian-Early Triassic, the paleo-Asian ocean basin closed. The latest fold structure in the southern and northern basins of paleo-Asian Ocean and the direct relation with Tarim platform are probably caused by the late tectonic movement.