西藏冈底斯带中南部与俯冲有关的早侏罗世花岗闪长岩:锆石U-Pb年代学及地球化学证据  

Subduction-Related Early Jurassic Granodiorite in Xiaodasongdu,the South of Middle Gangdise in Tibet :Evidences from Zircon U-Pb Geochronology and Geochemistry

作　　者：陈炜[1,2] 马昌前[1] 宋志强[2] 龙桃成[2] 夏天齐[2] 蔡立元[2] 王彤[2] 

机构地区：[1]中国地质大学地球科学学院,武汉430074 [2]湖北省鄂东北地质大队,湖北孝感432100

出　　处：《地质科技情报》2011年第6期1-12,共12页Geological Science and Technology Information

基　　金：中国地质调查局矿产资源补偿费矿产勘查项目(H46E014011)

摘　　要：肖打松多花岗闪长岩位于西藏冈底斯花岗岩带中段以南,主要岩石类型有:细中粒黑云母(角闪石)花岗闪长岩、细中粒含斑黑云母(角闪石)花岗闪长岩、细中粒斑状黑云母(角闪石)花岗闪长岩,岩石具钙碱性特征,w(SiO2)=61.58%～72.16%,w(K2O)/w(Na2O)=0.64～1.15,相对富钠,A/CNK=1.25～1.43,w(Al2O3)变化于11.45%～16.00%之间,为准铝质岩石,花岗闪长岩岩体稀土元素总量w(∑REE)变化于152.10×10-6～251.22×10-6之间;轻稀土元素富集,负Eu异常较明显,以富K、Rb、Ba、Th等大离子亲石元素和亏损Nb、Y、Yb等高场强元素为特征。岩石学和岩石地球化学研究表明,该时期的花岗闪长岩具俯冲I型花岗岩的特点,形成于板块俯冲下的岛弧环境。用SHRIMP测定肖打松多花岗闪长岩体锆石的U-Pb年龄为(191.9±1.1)Ma。同时表明冈底斯岩浆弧带在早侏罗世岩浆曾经剧烈地活动过,肖打松多岩体是新特提斯洋向北俯冲作用的产物。Granodiorite is located in Xiaodasongdu region in the southern part of the middle Gangdise granitoid belt in Tibet.The main rock types include biotite granodiorite,porphyry-bearing biotite（hornblende） granodiorite,and porphyritic biotite granodiorite.The rocks are calc-alkaline and relatively rich in sodium,with SiO2 content between 61.58%-72.16%,K2O/Na2O=0.64-1.15 and A/CNK=1.25-1.43.Al2O3 varies from 11.45% to 16.00 %,which proves that the rock is the aluminum rock.While the total amount of ΣREE in the granodiorite changes in a range from 152.10×10-6 to 251.22×10-6.The rock is characterized by enrichment of the light REE,obvious negative Eu anomaly,rich K,Rb,Ba,Th,and other large ion lithophile elements（LIL） and loss of Nb,Y,Yb high field strength elements.The petrology and geochemistry researches show that the granodiorite of this period has the characteristics of I-type granite formed in the island arc environment with plate subduction.The U-Pb age of zircon in the rock mass of Xiaodasongdu granodiorite is dated（191.9±1.1）Ma by SHRIMP.This also implies that the Gangdise magmatic arc was very active in Early Jurassic and so the Xiaodasongdu rock mass should be the product of the northward subduction of new Tethys.

关 键 词：早侏罗世花岗闪长岩 SHRIMPU-Pb年龄 锆石 地球化学 肖打松多 西藏 

分 类 号：P588.12[天文地球—岩石学]