西秦岭北缘关子镇蛇绿岩的形成时代:来自辉长岩中LA-ICP-MS锆石U-Pb年龄的证据  

LA-ICP-MS Zircon U-Pb Dating of the Gabbro from the Guanzizhen Ophiolite in the Northern Margin of the Western Qinling and Its Geological Significance

作　　者：裴先治[1] 丁仨平 李佐臣[1] 刘战庆[1] 李高阳[1] 李瑞保[1] 王飞[1] 李夫杰[1] 

机构地区：[1]西部地质资源与地质工程教育部重点实验室,长安大学地球科学与资源学院,西安710054

出　　处：《地质学报》2007年第11期1550-1561,共12页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40572121;40234041);教育部科学技术研究重点项目(编号104175);中国地质调查局地质调查项目(编号200013000154)资助的成果。

摘　　要：西秦岭北缘天水地区关子镇蛇绿岩由变质基性火山岩(斜长角闪片岩)和蛇纹岩、变辉石岩、变辉长岩等构造岩块组成。其中的变质基性火山岩具有N-MORB的地球化学特征,显示关子镇蛇绿岩是洋脊型蛇绿岩残片。对蛇绿岩中的辉长岩进行了LA-ICP-MS锆石U-Pb定年,得到206Pb/238U加权平均年龄为(499.7±1.8)Ma(MSWD=2.2),代表了辉长岩的结晶年龄,表明关子镇蛇绿岩是晚寒武世在西秦岭北缘李子园—关子镇—武山洋盆扩张过程中岩浆活动的产物,代表了东秦岭早古生代商丹古洋盆在西秦岭造山带北缘向西延伸的组成部分。The Guanzizhen ophiolite in the Tianshui area, located in the northern margin of the western Qinling,is composed of metamorphic basic volcanic rock and massive rocks such as serpentinite, metapyroxeniteand metagabbro. The geochemical features of metamorphic basic volcanic rock show its N-type MORB,indicating that the Guanzizhen ophiolite is the remains of the oceanic ridge ophiolite. LA-ICP and MSzircon U-Pb dating of gabbro from the Guanzizhen ophiolite suggests an isotopic age of 499. 7 -＋- 1. 8Ma（MSWD = 2. 2）, which indicates that the Guanzizhen ophiolite was the product of magmatic activity during the process of extension of Liziyuan-Guanzizhen-Wushan ocean basin along the northern margin of the Western Qinling in the late Cambrian, and was a component of the Shangda paleobasin during Paleocene which extended westward along the northern margin of the Qinling orogenic belt.

关 键 词：蛇绿岩 辉长岩 LA-ICP-MS 锆石U-Pb年龄 晚寒武世 天水地区 西秦岭 

分 类 号：P588.1[天文地球—岩石学]