东准噶尔构造带晚古生代地层时代的厘定及其对区域构造演化意义

Redefinition of Formation Age of Late Paleozoic Strata in the Eastern Junggar Tectonic Zone and Its Implications for Evolution of Regional Geological Structure

新疆东准噶尔（东准）构造带晚古生代地层广泛出露,其沉积时限的精确限定对理解该地区及中亚造山带的构造框架具有深远意义。然而东准构造带的地层时代标定存在多种划分方案,分歧较大。依据自测的5个安山岩和9个砂岩的锆石U-Pb年龄以及收集整理的岩浆岩和砂岩的锆石U-Pb年龄约束,认为东准噶尔构造带地质体的形成时代主要在336~268Ma,〉336Ma地质体沿额尔齐斯、阿尔曼太和卡拉麦里构造带零星分布。原前石炭纪和原石炭纪海相地层主体属于石炭系宾夕法尼亚亚系,部分层段应为同期异相;原石炭纪陆相地层属于二叠系乌拉尔统。东准构造带晚古生代洋盆在晚石炭世同期碰撞拼贴,将其演化阶段分为400~336Ma次生洋盆同期俯冲阶段、336~300Ma洋盆最终闭合消亡阶段、300~270Ma后碰撞伸展阶段及二叠纪中晚期南缘湖相沉积阶段。

The accurate dating of Late Paleozoic strata,which are widely exposed in the eastern Junggar,Xinjiang,is of profound importance for establishing the tectonic framework of the eastern Junggar and the central Asian orogenic belt.Several schemes for the chronostratigraphic classification have been proposed,but there are many differences about these schemes.This study carried out zircon U-Pb dating for five andesite samples and nine sandstone samples.Combined with previously published age data for zircons from magmatic rocks and sanstone,the data in this study indicate that the formation age of the most geological bodies was formed between 336 Ma and 268 Ma,with several bodies with ages 336 Ma sporadically exposed mainly along Erqix,Armantai and Kelameili tectonic zones.Most of preCarboniferous and Carboniferous marine strata should belong to the Pennsylvanian System,with part being contemporaneous heteropical sediments.The Carboniferous continental strata should be Permian Cisuralian series.The Late Paleozoic oceanic basin in eastern Junggar underwent contemporaneous subduction-collision.Its tectonic evolution can be divided into three stages：contemporaneous subduction of secondary oceanic basin during 400~336 Ma,closure stage of oceanic basin during 336 — 300 Ma,and post-collision stage during 300~270Ma as well as lacustrine deposition stage in the southern margin during middle-late Permian.