中祁连西段北大河岩群中早古生代火山碎屑岩的识别——来自锆石U-Pb年代学的证据

SHRMP U-Pb Geochronological Verification on the Identification of Early Paleozoic Volcanic Clasolite Zircons from the Beidahe Complex-Group in the Western Segment of the Middle Qilian Mountains, China

摘要: 前人认为北大河岩群是祁连造山带西段最古老的变质岩系之一.笔者在肃北地区该岩群中发现了变质中基性凝灰岩,并对其进行了锆石的LA-ICP-MS U-Pb同位素测定,分析结果表明,该中基性凝灰岩的形成年龄为(444±6.9)Ma,可能为中祁连地块在早古生代发生构造岩浆活动的产物,而并非北大河岩群物质组分.笔者根据野外露头、变质程度及年代学数据将其从北大河岩群中解体出来,并将其重新归属于中下奥陶统吾力沟组.笔者研究结果将为探讨中南祁连的物质组成和地质演化历史提供新的约束材料.

Abstract: Previous researchers thought Beidahe Complex-Group was one of the oldest metamorphic rocks in the western part of the Qilian orogenic belt. However, according to the SHRMP U-Pb zircon data of the mafic tuffs from the Beidahe Complex-Group in Subei area reported in the paper, the intermediate-basic tuffs were formed in (444±6.9) Ma, and they might be the product of early Paleozoic tectonic-magmatic activity in Mid-Qilian area rather than material compositions of Beidahe Complex-Group. The authors separated the tuff from Beidahe Complex-Group and re-attributed it to Wuligou Formation of Ordovician Series. The results of this study will provide new materials for exploring material composition and geological evolution of middle-south Qilian.