西藏冈底斯构造带申扎一带寒武系火山岩的发现及其地质意义

Discovery of the Cambiran volcanic rocks in the Xainza area, Gangdese orogenic belt, Tibet, China and its significance

摘要: 冈底斯构造带中段申扎一带存在下奥陶统阿雷尼格阶最底部的笔石化石带Tetragraptus approximatus，其下伏有一套浅变质的火山-碎屑岩地层，对其中的流纹岩采用锆石LA-ICP-MS测年，获得14个点的加权平均206Pb/238U年龄为（500.8±2.1）Ma，首次确定了冈底斯中西部地区寒武系的存在。根据地层组成初步分析，其形成时处于浅海相沉积环境，为活动构造背景，同时指出冈底斯构造带寒武系的存在并非是局部现象，很可能有一定的分布范围。

Abstract: There is Tetragraptus approximatus, the typical graptolite fossil cluster which distribute in the bottom part of Arenigian of Early Ordovician in Xainza area, Gangdese orogenic belt. In situ zircon 206Pb/238U LA-ICP-MS dating on the rhyolite magmatic genetic zircons yielded a weighted average age of the (500.8±2.1)Ma; this has confirmed the existence of Cambrian sediments in the mid-west part of Gangdese orogenic belt for the first time. It′s indicated by the primary composition analysis that it is formed in shallow marine deposition and active tectonic setting, it also shows that the existence of Cambrian strata are not only local in Xainza County, but also in larger area.