狮泉河地区晚侏罗世—早白垩世火山岩锆石U-Pb年龄及成因

LA-ICP-MS Zircon U-Pb Age and Petrogenesis of the Late Jurassic to Early Cretaceou Volcanic Rocks in Shuquan River Area, Western Tibet

本文对狮泉河一带的则弄群火山岩进行了系统的年代学及元素地球化学研究。则弄群火山岩主要有英安岩、玄武岩、安山岩等组成,根据本区地球化学分析数据将其分为酸性(>63%)和中基性(<63%)两个组。而酸性主要位于高钾钙碱性系列,中基性以低钾和中钾钙碱性为主;二者微量元素分布特征相似,如均富集Rb、U、Th、K等大离子亲石元素(LILE),Nb、Ti、Ta等高场强元素(HFSE)有着明显的负异常,具有明显的岛弧型火山岩的特征;根据锆石U-Pb LA-ICP-MS定年获取了145.9±1.9Ma、148.5±1.5Ma年龄,说明研究区则弄群火山岩形成于晚侏罗世-早白垩世,表明狮泉河结合带在玩侏罗世-早白垩世已发生俯冲作用。

In the paper,majar,trace element compositions and Zicron U-Pbdataing results of the Zenong volcanic rocks in Shiquan River have been reported.The volcanic rocks from the Zenong Group mainly contain basalt,andesite,dacite and rhyolite.BasedonThe geochemical composition,these volcanic rocks are divided into two groups:the intermediate-basic group(SiO2<63%)and acid group(SiO2>63%).The majar element geochemistry of the intermediate-basic group Zenong Group volcanic rocks belong to low potassium calc-alkaline series.mediatebasic group Zenong Group volcanic rocks belong to high-K calc-alkaline series;the two grops show a similar trace element characteristic,being enriched inLILE such as Rb,Th,U,K and depleted in HFSE such as Mb,Ta,Ti,which shows island-arcvolcanic characteristics.The zircon U-Pb weighted average age measured by LA-ICP-MS is 145.9±1.9、148.5±1.5 Ma.It is concluded that subduction took place in Late Jurassic to Early Cretaceou in the Shiquanhe suture.