南秦岭武当群锆石SHRIMP U-Pb定年及其地质意义

武当群是南秦岭基底岩系的重要组成部分，对其时代及构造性质的研究，对认识南秦岭早期地质演化历史及其与扬子板块新元古代的相互关系具有重要的意义。目前，武当群的时代归属、划分对比还存在较大争议。本文对采自南秦岭西峡-内乡和陨西地区武当群4件变质酸性火山岩及1件侵入武当群的花岗斑岩样品进行了锆石SHRIMP U-Pb同位素定年，其中采自西峡-内乡接近武当群底部的1件火山岩样品的年龄为802±13 Ma，这一年龄可代表武当群底部地层的时代；采自该群中上部的3件火山岩样品，年龄分别为725±9 Ma、732±6 Ma和725±7 Ma；1件侵入武当群的花岗斑岩样品的年龄为703±5 Ma。根据上述结果，结合前人对武当群的研究资料，确定武当群的形成时代为810~720 Ma，相当于扬子地台板溪群；介于武当群与震旦系之间的耀岭河群可与南华系对比。

Zircon SHRIMP U-Pb dating of the Wudang Group in South Qinling belt and its geological significance

Wudang Group is an important part of the South Qinling basement, and therefore the study of its age and structural property is of great significance for understanding the early geological evolution history of the South Qinling belt and its relationship with the Yangtze plate in the Neoproterozoic. At present, the age, division and comparison of Wudang Group are still controversial. In this paper, zircon SHRIMP U-Pb isotope dating was performed on 4 metamorphic acid volcanic rocks from Wudang Group and 1 granite porphyry invading the group in the Xixia-Neixiang-Yunxi area. The age of a sample located at the bottom of Wudang Group in the Xixia-Neixiang area is 802±13 Ma, which can represent the age of the bottom strata of Wudang Group. In addition, 3 volcanic samples collected from the middle-upper part of the group were formed at 725±9 Ma, 732±6 Ma and 725±7 Ma respectively, and meanwhile the age of the granite porphyry is 703±5 Ma. Based on the above results and combined with previous research data on Wudang Group, it is determined that the formation time of Wudang Group is 810~720 Ma, equivalent to the age of Banxi Group of the Yangtze plate, while the Yaolinghe Group between the Wudang Group and the Sinian could be compared with the Nanhua System.