塔里木盆地东南缘早古生代弯山构造

位于塔里木盆地东南缘的阿尔金地区发育南、北两条早古生代缝合带,通过对带内出露的大量早古生代蛇绿岩、高压-超高压变质岩以及不同性质的花岗岩的同位素年代学资料的收集、整理和对比,发现南、北缝合带内岩体在岩石学、地球化学、形成的时代和构造环境等方面具有可对比性,推测在早古生代两者处于同一个俯冲带体系中,只是演化时限存在沿走向的穿时性。本文提出,阿尔金造山带为一弯山构造,我们称之为塔里木盆地东南缘早古生代弯山构造。通过古地磁资料与板块重建的研究与分析,揭示了塔里木-柴达木陆块在早古生代很可能作为一个整体漂移,发生了以逆时针方向为主的相对旋转,这与弯山构造的形成息息相关。在原特提斯洋向南斜向俯冲闭合过程中,分布在大洋中的塔里木-柴达木陆块、中阿尔金-中祁连微陆块以及其他亲冈瓦纳古陆的微陆块组成的链状陆块群,形成了近直线型的俯冲造山带。在斜向俯冲-碰撞机制下,塔里木-柴达木陆块的逆时针旋转,诱发了大型韧性剪切带和右行走滑断裂带,加之微陆块间的俯冲-碰撞相互作用的影响,最终导致初始造山带发生弯曲。塔里木盆地内发育的早古生代构造不整合以及呈"S"形展布的古构造、油气藏分布形态恰好为其提供了佐证。对塔里木盆地东南缘早古生代弯山构造的研究,不仅有助于增进对原特提斯洋俯冲、闭合的理解和认识,还可以为建立中央造山带的演化模式提供新的思路。

The Early Paleozoic orocline in the southeastern Tarim Basin

There are two Early Paleozoic suture zones exposed in the North and South Altun area respectively, located in the southeastern Tarim Basin, NW China. By collecting and analysing the data of ophiolites, metamorphic rocks as well as Early Paleozoic granites in both of the two sutures, it is revealed that the North Altun suture shares a great similarity with the south in their petrology, geochemistry, especially isotopic geochronology, which indicated that both sutures might belong to the same subduction system during the Early Paleozoic. And the difference of them is due to diachronism of evolutionary timing along the orogenic belt probably. In this paper, we propose that the Altun orogenic belt is an orocline, called the Southeastern Tarim Orocline. By the studies on the paleomagnetic data and plate reconstruction results, it can be found that the Tarim and Qaidam micro-continents were likely to drift as a whole after splitting from Gondwana. Besides, it rotated counterclockwise relatively in the Early Paleozoic, which is related with the formation of the orocline closely. And a chain-like superterrane, composed of the Tarim-Qaidam micro-continent, the Central Altyn-Qilian micro-continent and other Gondwana-affinity micro-continents, was formed and located in the Proto-Tethys Ocean. During the southward subduction and closure of the ocean, a nearly linear subduction orogenic belt was formed at the northern margin of the superterrane. Owing to the oblique subduction-collision mechanism, the Tarim-Qaidam micro-continent rotated counterclockwise, and large ductile shear zones and dextral strike-slip faults were generated, which all bent the orogen. Finally, the interaction of the tectonic movements among the micro-continents made the "S"-shaped Southeastern Tarim Orocline take shape in the late Early Paleozoic. The study of the Southeastern Tarim Orocline could not only help to improve the understanding of the Proto-Tethys Ocean closure, but also provide a new perspective on the evolution of the Central China Orogen.