新疆西准噶尔地区花岗岩类年代学及其构造意义

本文在野外地质调查基础上,通过对西准噶尔花岗岩类年代学的研究,厘定各期构造岩浆事件的时限,反演西准噶尔造山带构造演化过程。研究结果表明,西准噶尔岩浆活动划分为3个时期。晚志留世—早泥盆世花岗岩类主要为谢米斯台花岗岩类、赛尔花岗岩类及阿克乔克花岗岩类,结合区域地质背景及阿克乔克花岗闪长岩具有典型的埃达克岩地球化学特征,推测阿克乔克埃达克岩可能是大洋板片俯冲过程中经过脱水发生部分熔融形成的;早石炭世花岗岩类主要分布在扎尔马—萨吾尔岩浆弧地区,这一时期的花岗岩类可能是额尔齐斯蛇绿岩所代表的古大洋向南俯冲脱水引发上覆地幔楔部分熔融或者部分熔融形成的玄武岩浆底侵作用引起中、下地壳物质部分熔融的结果,指示俯冲的古大洋在早石炭世期间未闭合碰撞;晚石炭世—早二叠世的花岗岩类在整个西准噶尔地区都有分布,形成于后碰撞构造环境,表明西准地区进入了陆内构造演化阶段。

Geochronology and Tectonic Implications of the Granites in West Junggar, Xinjiang

Based on the chronological study of the granites in West Junggar,Combined with the detailed field investigations,Time limits for the tectonic events and tectonic evolution of West Junggar are further established.The results of the study show that the magmatic activities in the West Junggar is divided into three periods.Late Silurian-early Devonian magmatic event produced mainly Akeqiaoke,Ximisitai,and Saier granitoids,and Akeqiaoke granodiorites having geochemical characteristics of typical adakite resulted from the partial melting of subducted oceanic slab;The early Carboniferous granites distributed mainly in the Zharma-Saur volcanic arc region,and produced by either partial melting of the the mantle wedge related to ancient oceans,represented by Irtysh ophiolite,southward subducted,or partial melting of lower crust related to basaltic magma underplating;The Late Carboniferous-Early Permian of granites in West Junggar,formed in post-collision,showing West Junggar had began to intra-continental tectonic evolution.