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.该岩体中的锫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206 Pb/238U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.%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 2 Pb/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 Songpan-Garze 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.
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