阿尔泰造山带南缘基性杂岩的形成背景及其动力学含义

Tectonic setting of mafic rocks in southern Altay orogenic belt and its geodynamic implication.

新疆北部阿尔泰造山带南缘出露-套基性杂岩，它们呈透镜状存在于晚古生代片麻状花岗岩中。阿拉尕克基性杂岩的^40Ar／^39Ar坪年龄为262．7±1．1Ma。基性杂岩的地球化学分析结果显示阿勒泰阿拉尕克、塔尔浪乡样品的轻、重稀土元素基本上没有发生分异，富蕴县乌恰沟基性岩的轻、重稀土元素发生了中-弱的分异；在微量元素特征方面，富集Th、Rb。通过地球化学图件判别，认为该基性杂岩形成于海山的构造环境。结合前人获得的花岗岩锆石SHRIMP的年代集中在400-410Ma左右，而花岗岩^40Ar／^39Ar坪年龄为240Ma左右，作者认为基性杂岩的^40Ar／^39Ar坪年龄代表了晚二叠世时期的一次构造事件的年龄，基性杂岩寄生于花岗岩中是通过构造混杂作用实现的。在此基础上，提出了形成过程的两个阶段，即：晚古生代早期的俯冲阶段，为花岗岩与含海山玄武岩的增生楔形成阶段，晚二叠世的强烈碰撞阶段，导致花岗岩和增生楔物质的变形和构造混杂。

Located in southern Altay orogenic belt, North Xinjiang, a suit of mafic rocks exhibited lentoid in Late Paleozoie gneissic granite. ^40 Ar/^39 Ar dating of mafic rocks in Alagak yielded plateau age of 262.7 ± 1.1 Ma. Geochemical analysis of samples in Alagak, Taerlang and along Buerjin-Altay highway shows that there are no differentiation between LREE and HREE, while in Wuqiagou, Fuyun County shows mid-light differentiation. These mafic rocks are enriched in Th and Rb, but depleted in Nb and Zr which is similar to seamount basahs. The discriminate figures of tectonic setting show that the mafic rocks were formed in .seamount basalts. Combined with the ages of 400 - 410Ma by SHRIMP U-Pb dating of zircons and 240Ma by ^40Ar/^39Ar plateau age in granite from the literature, the authors suggest that age of ^40Ar/^39Ar dating represents a tectonic event happened at late Permian and mafic rocks parasited in granites was caused by a tectonic event. Assemblage of mafic rocks and granite is due to tectonic chaotic assemblage. Conclusively, two stages of formation were proposed： （1） during subduction stage in the early of Late Paleozoic, in which granites and accretionary prism containing seamount basalts formed, and （2） during intensive collision stage, in which granites and aecretionary prism experienced tectonic deformation and mixture.