藏东卡贡地区早侏罗世似斑状钾长花岗岩LA-ICP-MS锆石U-Pb年龄及地球化学特征  

LA-ICP-MS zircon U-Pb age and geological characteristics of the Early Jurassic potassium porphyritic granites in Kargang area,eastern Tibet

作　　者：于涛[1] 徐佳丽[2] 高强 樊炳良 徐长昊[5] YU Tao;XU Jiali;GAO Qiang;FAN Bingliang;XU Changhao(College of Science,Tibet University,Lhasa 850000,Tibet,China;School of environmental studies,China University of Geosciences(Wuhan),Wuhan 430074,Hubei,China;The Fourth Geological Brigade of Hebei Geological and Mining Bureau,Chengde 067000,Hebei,China;Geothermal Geological Survey Party,Tibet Bureau of Geology and Mineral Exploration and Development,Lhasa 850000,Tibet,China;Department of Geology College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,Sichuan,China)

机构地区：[1]西藏大学理学院,西藏拉萨850000 [2]中国地质大学(武汉)环境学院,湖北武汉430074 [3]河北省地矿局第四地质大队,河北承德067000 [4]西藏自治区地质矿产勘查开发局地热地质大队,西藏拉萨850000 [5]成都理工大学地球科学学院,四川成都610059

出　　处：《地质通报》2020年第5期621-630,共10页Geological Bulletin of China

基　　金：中国地质调查局项目《西藏卡贡地区1∶5万四幅区域地质调查》(编号:DD20160016-21)。

摘　　要：用LA-ICP-MS技术测得卡贡地区似斑状钾长花岗岩锆石的206Pb/238U年龄为178±2 Ma(MSWD=3.7,n=20),属于早侏罗世的产物。岩石地球化学特征表明,岩石具富碱富钾(K2 O+Na2 O=8.02%~8.76%,K2 O/Na2 O=1.71~2.11)、低铝(Al2O 3=14.08%~14.73%,A/CNK=1.01~1.04),不含透辉石和刚玉分子较低的特征;岩石普遍富集Rb、Th、K、U等大离子亲石元素,明显亏损Ba、Nb、Sr、P、Ti等元素,高场强元素Zr、Nb、Ta含量极低,(Ga/Al)×10^4值为4.48~5.06,Rb/Sr值为1.84~2.29,均显示出岩浆分异程度较高的特征;岩石的形成与俯冲消减作用有关,其构造环境由挤压环境逐渐向相对伸展环境转变,伴随着地壳深部压力减小,幔源岩浆上涌,并与上覆地壳发生部分熔融作用而形成。In this paper,LA-ICP-MS zircon U-Pb age test was carried out on the potassium porphyritic granites in the Kargang area,which shows that the 206Pb/238U age weighted average value of the rock mass is 178±2 Ma(MSWD=3.7,n=20),suggesting a product of Early Jurassic.The geochemical characteristics of the rocks show that the rocks have alkali-rich potassium(K2O+Na2O=8.02%~8.76%,K2O/Na2O=1.71~2.11),but low aluminum(Al2O3=14.08%~14.73%,A/CNK=1.01~1.04),without pyroxene and with lower corundum molecules.The rocks are generally characterized by rich Rb,Th,K,U and other large ionic pro-stone elements,obvious loss of Ba,Nb,Sr,P,Ti and other elements,and very low values of high field strength elements Zr,Nb,with(Ga/Al)×10^4 values of 4.48~5.06 and Rb/Sr ratios of 1.84~2.29,which shows the characteristics of high magma differentiation;in addition,the formation of rocks was related to subduction reduction,and its tectonic environment changed gradually from extrusion environment to relative stretching environment,accompanied by the decrease of deep crustal pressure,which led to the upwelling of mantle source magma and the partial melting of the overlying crust.

关 键 词：似斑状钾长花岗岩 地球化学特征 锆石U-Pb LA-ICP-MS 岩石成因 

分 类 号：P534.52[天文地球—古生物学与地层学] P588.12[天文地球—地质学]