有关内蒙古西拉木伦带古生代-早中生代构造环境的讨论

针对近年来对华北板块与南蒙微大陆碰撞时限与演化历史的争论,本文通过内蒙古西拉木伦河两侧双井-杏树洼一带不同时期地质体的解析,反演了与古生代-中生代构造演化有关的三段历史:(1)由杏树洼组和所裹挟的蛇绿岩块组成的小苇塘岩片记录了早古生代末弧前盆地演化的历史;(2)由早二叠世末期侵位的中-基性岩墙和中二叠世的克德河砂砾岩充填的断陷盆地显示了板块碰撞造山后年轻陆壳经受的伸展作用;(3)中二叠世和中三叠世伸展背景下的岩浆活动,根据兴蒙造山带乃至中亚造山带岩浆活动的研究,结合前人对双井地区的研究成果,认为控制这一岩浆活动的是幔源岩浆上涌的底侵作用,而不是"同碰撞"的挤压-汇聚环境,因此花岗岩的形成不能作为板块碰撞时间的约束。

A reflection on the Xarmoron tectonomagmatic belt, Inner Mongolia, China

In connection with the recent debates on the timing and evolution history of the collision of the North-China Plate with the South-Mongolia microcontinent, three stages of the Paleozoic-Mesozoic plate tectonic evolution history of the concerned area are reconstructed through analysis of the geological bodies in different periods of the Shuangjing-Xingshuwa region on both sides of Xilamulun River in Inner Mongolia. (1) Development of the fore-arc basin in the end of the Earth Paleozoic as recorded by the Xiaoweitang rock slices composed of Xingshuwa formation with ophiolite blocks within. (2) Extension of the young continental crust after plate-collision orogeny as illustrated by the intermediate-basin dykes of later Early Permian and the graden basin filled with the Kedehe sand-conglomerates of Zhesi Formation of Middle Permian. (3) The magmatic activity related to extensional settings in the Middle Permian and Middle Triassic as reflected in the granites of the research area, which is, according to the settings of the magmatic activity of the Hinggan-Mongolia orogen as well as the Central Asia orogen and based on previous studies on the Shuangjing granites, controlled by underpleting of the upwelling mantle source magma in extensional settings rather than by any "syn-collisional" compression-convergence environment and, therefore, formation of the granites could not be seen as a constraint on the timing of the plates collision.