山西临县紫金山碱性杂岩内二长岩锆石U-Pb年代学及其意义  

U-Pb Zircon Geochronology of the Zijinshan Alkaline Intrusive Complex, Shanxi Province,and Its Geological Significance by using LA-ICP-MS

作　　者：张宏法[1,2] 陈刚 鲍洪平[3] 王润三[1,2] 马占荣[3] 彭天朗[1,2] 

机构地区：[1]大陆动力学国家重点实验室,陕西西安710069 [2]西北大学地质学系,陕西西安710069 [3]中石油长庆油田勘探开发研究院,陕西西安710021

出　　处：《矿物学报》2011年第1期70-79,共10页Acta Mineralogica Sinica

基　　金：大陆动力学国家重点实验室自主研究课题(编号:DJ081331)

摘　　要：山西临县紫金山杂岩主要由深成相岩瘤、浅成相岩墙和岩基、喷出相熔岩和火山角砾岩等岩石单元组成。对该杂岩体内的浅成相次透辉二长岩、霞辉正长岩进行了锆石LA-ICP-MS原位U-Pb同位素测年。结果显示,次透辉二长岩锆石边部U-Pb年龄加权平均值为(136.7±6.5)Ma,Th/U比值0.781～2.559,明显呈三段性,表明岩浆同化混染过程中岩浆成分变化的岩浆混合过程信息;锆石核部U-Pb年龄加权平均值为(1937±37)Ma,Th/U比值为0.339～0.669,显示岩浆成因特征;(霓)霞(次透)辉正长岩的锆石U-Pb加权平均年龄为(137±2.7)Ma,Th/U比值1.484～5.0,反映岩浆富Th且与二长岩互补的特征,揭示出这2期岩浆之间存在有限混合现象。2个样品年龄均显示紫金山碱性杂岩体最早的二长岩与霞辉正长岩浆活动在早白垩世。二长岩的2个孤点年龄(222±4)Ma和(323±3)Ma可能代表了霓霞钛辉岩、正霞正长岩及白霞正长岩包体岩石岩浆底侵的年龄。The Zijinshan alkaline intrusive complex,located in the eastern margin of the Ordos Basin,mainly consists of salite monzonite,diopside syenite,and nepheline-diopside syenite.This paper presented the zircon LA-ICP-MS data of U-Pb in salite monzonite and salite syenite from the Zijinshan alkaline complex.Zircon rims from salite monzonite sample are magmatic genesis with oscillatory and sector zoning,and have Th/U ratios of 0.781 to 2.559,with ^206Pb/^238U age of 136.7±6.5 Ma.The inherited zircon cores is from the same sample,with Th/U ratios ranging from 0.3390.669,and a weighted mean ^207Pb/^206Pb age of 1937±37 Ma.Zircons from the salite syenite have Th/U ratios ranging from 1.484 to 5.0,and give a weighted mean ^206Pb/^238U age of 137±2.7 Ma,which is consistent with the U-Pb age of salite monzonite,indicating that the Zijinshan alkaline intrusive complex occurred in the Early Cretaceous.In addition,the other two zircon grains from monzonite yield ^206Pb/^238U apparent ages of 222±4 Ma and 323±3 Ma,respectively,probably representing the timing of the magma underplating.

关 键 词：次透辉二长岩 霞辉正长岩 LA-ICP-MS 锆石U-PB年代学 山西临县紫金山 

分 类 号：P579[天文地球—矿物学] P581[天文地球—地质学]