关于古亚洲洋构造演化研究的几点思考

古亚洲洋不是西伯利亚陆台和华北地台间的一个简单洋盆，而是在不同时间、不同地区打开和封闭的多个大小不一的洋盆复杂活动(包括远距离运移)的综合体.其北部洋盆起始于新元古代末-寒武纪初(573~522Ma)冈瓦纳古陆裂解形成的寒武纪洋盆.寒武纪末-奥陶纪初(510~480Ma)，冈瓦纳古陆裂解的碎块、寒武纪洋壳碎块和陆缘过渡壳碎块相互碰撞、联合形成原中亚-蒙古古陆.奥陶纪时，原中亚-蒙古古陆南边形成活动陆缘，志留纪形成稳定大陆.泥盆纪初原中亚-蒙古古陆裂解，裂解的碎块在新形成的泥盆纪洋内沿左旋断裂向北运动，于晚泥盆世末到达西伯利亚陆台南缘，重新联合形成现在的中亚-蒙古古陆.晚古生代时，在现在的中亚-蒙古古陆内发生晚石炭世(318~316Ma)和早二叠世(295~285Ma)裂谷岩浆活动，形成双峰式火山岩和碱性花岗岩类.蒙古-鄂霍次克带是西伯利亚古陆和中亚-蒙古古陆之间的泥盆纪洋盆，向东与古太平洋连通，洋盆发展到中晚侏罗世，与古太平洋同时结束，其洋壳移动到西伯利亚陆台边缘受阻而向陆台下俯冲，在陆台南缘形成广泛的陆缘岩浆岩带，从中泥盆世到晚侏罗世都非常活跃.古亚洲洋的南部洋盆始于晚寒武世.此时，华北古陆从冈瓦纳古陆裂解出来，在其北缘形成晚寒武世-早奥陶世的被动陆缘和中奥陶世-早志留世的沟弧盆系.志留纪腕足类生物群的分布表明，华北地台北缘洋盆与塔里木地台北缘、以及川西、云南、东澳大利亚有联系，而与上述的古亚洲洋北部洋盆没有关连，两洋盆之间有松嫩-图兰地块间隔.晚志留世-早泥盆世，华北地台北部发生弧-陆碰撞运动，泥盆纪时，在松嫩地块南缘形成陆缘火山岩带，晚二叠世-早三叠世华北地台与松嫩地块碰撞，至此古亚洲洋盆封闭.古亚洲洋的南、北洋盆最后的褶皱构造，以及与塔里木地台之间发生的直接关系，很可能是后期的构造运动所造成的.

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.