四川九龙新火山花岗岩体单颗粒锆石LA-ICP-MS U-Pb定年及其地质意义

LA-ICP-MS zircon U-Pb dating and geological implications for the Xinhuoshan granites in Jiulong, Western Sichuan

摘要: 本文对四川九龙新火山花岗岩岩体中的锆石进行了详细的LA-ICP-MS U-Pb同位素年龄测定。该岩体中的锆石发育较好的环带结构,Th/U值较高(大于0.13),具有岩浆成因锆石的特征。研究结果表明,新火山岩体中锆石的²⁰⁶Pb/²³⁸ U加权平均年龄为181.2±1.4Ma(MSWD=3.3),代表了新火山花岗岩的结晶年龄,为早侏罗世,反映了松潘-甘孜造山带燕山期岩浆活动的一个重要阶段,为进一步理解松潘-甘孜燕山期花岗质岩浆活动及其动力学背景等提供了有力的证据。

Abstract: The LA-ICP-MS zircon U-Pb dating is made for the Xinhuoshan granites in Jiulong, Western Sichuan. The selected zircon grains from the granites display well-defined girdle structures in the cathodoluminescence images and higher Th-U ratios (more than 0.13) characteristic of magmatic origin. The ²⁰⁶Pb/²³⁸Pb weighted average age of 181.2±1.4 Ma (Early Jurassic) for the Xinhuoshan granites (MSWD=3.3) represents the age of crystallinization of the Xinhuoshan granites, and an important phase of the Yanshanian magmatism in the SongpanGarze orogenic zone. The findings in this study may serve as the circumstantial evidence for better understanding of the granitic magmatism and dynamic settings in the Songpan-Garze orogenic zone druing the Yanshanian.