中朝陆台北侧褶皱带构造发展的几个问题

中朝与西伯利亚陆台之间的乌拉尔—蒙古—鄂霍茨克褶皱系是古亚洲洋演化的结果。其发展分为两个大的阶段:早期阶段从中元古代起在北部形成蒙古—鄂霍茨克洋,到寒武纪初封闭,形成兴凯褶皱带;晚期阶段从震旦—寒武纪初起在南部形成乌拉尔—蒙古洋,到泥盆纪大洋封闭,形成早及中古生代褶皱带。这就是中朝与西伯利亚陆台边缘褶皱带发育不对称的原因。 乌拉尔—蒙古洋最后封闭的缝合带在内蒙古中部形成中古生代褶皱带。它包括贺根山蛇绿岩带,二道井—查干诺尔混杂体带和它们之间的锡林浩特花岗岩—变质岩带。后者是造山碰撞的中心,上泥盆统法门阶的磨拉石堆积主要沿此带分布。 石炭—二叠纪时,本区广泛兴起裂谷活动。这些裂谷发育在不同的基底之上,多数发生于不同时期构造带的界线上。它们在新增生的年青陆壳上形成,其特征不同于红海或东非型裂谷;其岩浆活动和变形、变质作用使年青陆壳增厚并更加稳固。

ON TECTONIC DEVELOPMENT OF THE FOLD BELTS IN THE NORTH MARGIN OF SINO-KOREAN PLATFORM

Abstract The area concerned in this paper belongs to the Tianshan-inggan fold system and is a part of the huge Urals-ongolia-khotsk fold system. In north of Sino-Korean and Talimu platforms the oldest ophiolite were formed in Sinian Cambrian; besides the Ondor Sum ophiolite, Dobretzov and Zonenshain (1985) showed widespread Sinian-ambrian ophiolite in western Mongolia, eastern Sayan, Tuva,western Sayan, Khazahstan and western Urals. They show that theUrals-Mongolian ocean op-ned and spreatled in Sinian and Cambrian. However, the Mongolia-Okhotsk ocean between the ancient microcontinents in the Xingkaiian fold belt and Siberian platform opened more earlier, with its spreading begining between 1600 Ma and 1400Ma ago and its consumption about 800Ma. Therefore, the intercontinental region between Sino-orean and Siberian platforms comprises two fold systems representing earlier Mongolia-Okhotsk ocean and later Urals-Mongolian ocean respectively. On the basis of our data, the time of collision between Sino-Korean and Siberian platforms ought to be Late Devonian or earlier. Late Late Devonian molasse is overlying unconformably the metamorphic rocks and the granites of Siliiihot belt, indicating the age of the continental crust there. This orogeny resulted from the collision between the two ancient continental plates and the Silinhot belt is the front of the collision. No oceanic enviroment was present in the region during Late paleozoic but continental rift structures widely developed on the accreted fold belts of various stages from Middle Proterozoic to Middle Paleozoic. However, they are different from the rift of East Africa type or Red Sea type and they are the rifts on newly accreted young continental crust under effect of newly opened Late Paleozoic ocean (the Old Pacific and Paleotethys). The magmatism and deformation-metamorphism of such rifting type thickened the young continental crust to be stabilized further. A brief model is given to show the plate tectonic evolution between the Sino-Korean and Siberian platforms in this paper.