扬子陆块西缘乌拉溪花岗岩体SHRIMP锆石U-Pb定年及地质意义

SHRIMP Zircon U-Pb Dating of the Wulaxi Granite in the Western Margin of the Yangtze Block and Its Geological Significance

乌拉溪花岗岩体位于扬子陆块西缘的江浪穹窿北侧,为精确厘定其形成时代并探讨岩石成因、构造意义及与里伍式铜矿的关系,对其进行了SHRIMP锆石U-Pb年代学研究。定年结果表明,乌拉溪花岗岩中发育940.3~199.6Ma的锆石,最年轻一组岩浆锆石206Pb/238U加权平均年龄为166.6±1.1Ma（MSWD=2.6,n=6）。结合前人研究成果,认为乌拉溪花岗岩体形成于~166.6Ma,接近邻近的文家坪花岗岩体结晶年龄（~161.5Ma）,可能均是松潘—甘孜造山带伸展构造背景下里伍岩群部分熔融的产物。2个岩体年龄大致代表江浪穹窿的成穹时代,后者可能发生于166.6~161.5Ma。此外,花岗岩体结晶年龄与金属硫化物Re-Os定年结果相近,表明江浪穹窿的Cu、W成矿可能与岩浆热液作用相关。

The Wulaxi granite is located in the north side of the Jianglang dome in the western margin of the Yangtze block.In order to accurately determine the formation age of the granite and discuss its petrogenesis,tectonic significance,and relationship with the Liwu-type copper deposits,the SHRIMP zircon U-Pb dating of the granite has been carried out in this study.The results show that the Wulaxi granite contains zircons of numerous ages varying from 940.3 Ma to199.6 Ma,with the youngest magmatic zircons having the206 Pb /238 U weighted mean age of 166.6 ± 1.1 Ma（MSWD =2.6,n = 6）.Combining with the previous studies,it is proposed that the Wulaxi granite was formed at ~ 166.6 Ma which was close to the crystallization age of the adjacent Wenjiaping granite（~ 161.5 Ma）.They both could be formed by the partial melting of the Liwu group under extensionalenvironment in the Songpan-Garze orogenic belt.The crystallization ages of two granite bodies（166.6-161.5 Ma） could roughly represent the formation age of the Jianglang dome.Moreover,the Re-Os ages of sulfides are close to the crystallization ages of the Wulaxi and Wenjiaping granites,indicating that the Cu and W mineralization coourred in the Jianglang dome were most likely associated with the magmatic hydrothermal fluid activities.