新疆东部新元古代晚期和古生代构造格局及其演变

Late Neoproterozoic and Paleozoic Tectonic Framework and Evolutionof Eastern Xinjiang, NW China

基于笔者近20年来对新疆东部地质构造的研究和对前人地质地球物理资料的深入分析,本文系统讨论了新疆东部新元古代晚期和古生代的地壳形成与演化。该区古生代的构造单元被划分为阿尔泰地块、额尔齐斯断裂带、东准噶尔古生代造山带、准噶尔地块、东天山造山带和库鲁克塔格地块。该区古生代地壳构造演化包括震旦纪—石炭纪洋陆格局的变迁、石炭纪末至二叠纪后碰撞壳幔相互作用等两个阶段。其洋陆格局的变迁包括古生代早期萨彦洋、早古生代阿尔曼太尔洋、晚古生代卡拉麦里洋、古生代北天山洋和南天山洋的打开与关闭,其中两个天山洋盆可能为一个洋盆,大体上可以对比为中亚地区的古亚洲洋北支斋桑洋,阿尔曼太洋和卡拉麦里洋可能为西伯利亚古陆的边缘洋盆;而古亚洲洋南支的乌拉尔—南天山洋向东是否延伸到新疆东部,还有待于进一步研究。新疆东部的后碰撞构造演化包括三期重大地质事件:① 300 Ma 前后的以中酸性为主的大规模岩浆活动;② 280 Ma 前后的包括幔源岩浆在内的双峰式岩浆活动;③ 二叠纪中晚期(可能延续到三叠纪)的大规模地壳走滑运动。在此基础上,对新疆东部新元古代晚期和古生代构造演化与古亚洲洋演变的关系进行了探讨,并对仍然存在的主要相关问题进行了总结和归纳。

Based on the author's investigations into the geological tectonics of the eastern Xinjiang region in the past 20 years and an analytical study of the previous geological and geophysical data,this paper systematically states the crustal formation and evolution of the eastern Xinjiang region during the late Neoproterozoic and Paleozoic. The Paleozoic tectonic framework of the region is divided into the Altay block, the Irtys faulting belt, the East Junggar orogen, the Junggar block, the East Tianshan orogen, and the Kuruktag block. The crustal evolution of the region consists of two stages, i. e. the Sinian to early Carboniferous evolution of oceanic and continental framework, and the late Carboniferous to Permian post-collisional crust-mantle interaction. The evolution of the ocean-continental framework is related to the opening and closure of the earliest Paleozoic Sayan Ocean, the Early Paleozoic Almatai Ocean, the Late Paleozoic Karamaili Ocean, and the Paleozoic north Tianshan and South Tianshan oceans. Of them, the Sayan Ocean separated the Altay block from the Siberian plate; the two Tianshan oceans might be connected to the Zhaisang Ocean between the Kazakhstan and Siberian plates, being a north branch of the Paleo-Asian Ocean; and the Almantai and Karamaili oceans were marginal ones of the Siberian plate. Whether the Ural-South Tianshan Ocean, a south branch of the Paleo-Asian Ocean, was extended into the eastern Xinjiang region remains to be investigated. Post-collisional tectonic evolution of eastern Xinjiang region is marked by three key geological events, which are the large-scale acid-intermediate magmatic activities about 300 Ma ago, the mantle-derived bi-modal magmatic activities about 280 Ma ago, and a large-scale strike-slip movement along major faults during the Middle-Late Permian. And then, the relationship between the tectonic evolution of the eastern Xinjiang region during the late Neoproterozoic to Paleozoic and that of the Paleo-Asian Ocean is discussed, and the major problems open to further studies are summarized.