冈底斯带西北缘别若则错地区晚白垩世闪长岩LA-ICP-MS锆石U-Pb测年、地球化学及地质意义  

LA-ICP-MS Zircon U-Pb Dating and Geochemical Analysis of the Late Cretaceous Diorite in the Bieruozecuo Area,Northwestern Margin of the Gangdise Belt,Tibet,and Their Geological Significances

作　　者：邱婵媛 肖倩茹[1] 魏永峰 罗巍[1,2] 杨亚民 肖渊甫[1] QIU Chanyuan;XIAO Qianru;WEI Yongfeng;LUO Wei;YANG Yamin;XIAO Yuanfu(College of Earth Sciences,Chengdu University of Technology,Chengdu,610059;Regional Geological Survey Team,Sichuan Geology and Mineral Bureau,Shuangliu,Sichuan,610213)

机构地区：[1]成都理工大学地球科学学院,成都610059 [2]四川省地质矿产勘查开发局区域地质调查队,四川双流610213

出　　处：《地质学报》2018年第11期2215-2226,共12页Acta Geologica Sinica

基　　金：西藏改则别若则错1:5万(I44E022020,I44E022021,I44E023020,I44E023021)4幅地质矿产调查项目(编号12120113036600)资助成果

摘　　要：别若则错地区闪长岩体呈不规则状、近椭圆状岩株侵位于早白垩世去申拉组或中酸性岩体中,内部可见少量暗色镁铁质包体。通过对闪长岩进行LA-ICP-MS锆石U-Pb测年,获得81.4±0.9Ma(MSWD=0.55)岩石结晶年龄,确认形成时代为晚白垩世。岩石具高K2O、低CaO特征,为准铝质高钾钙碱性系列岩石(KCG)。稀土元素总量为113.80×10-6～197.28×10-6,(La/Yb)N为11.98～20.26,δEu=0.83～0.98,球粒陨石标准化稀土元素配分模式表现为LREE相对富集的右倾分布,Eu亏损不明显;在原始地幔标准化比值蛛网图上,富集K、Rb,亏损Ba、Nb、P、Ce,类似于弧型火山岩。闪长岩地球化学成分具有明显的地幔和新生地壳双重特征,说明区内该类岩石是在地幔软流底辟作用下,由前期俯冲和碰撞间产生的地壳发生线性热隆及薄化减压、地幔热能和物质参与了地壳部分熔融和热隆伸展形成,形成环境为班公湖-怒江洋陆转换后碰撞伸展环境。Diorite in the Bieruozecuo area of Tibetoccurs in the Early Cretaceous Qushenla Group or intermediate-felsic rocks as irregular or elliptic stocks,with minor mafic enclaves.LA-ICP-MS zircon U-Pb dating of the diorite yields a crystallization age of 81.4±0.9 Ma（MSWD=0.55）,suggesting latein CaO,and should belong to quasi aluminum,high K and Ca,alkaline series rock（KCG）.The total～20.26and theδEu of 0.83to 0.98.Chondrite normalized REE patterns show relative enrichment of LREE,right-dipping distribution trend,and no obvious Eu depletion.Primitive mantle normalization spider diagram reveals enrichment of K and Rb and depletion of Nb and P,and these features are similar to that of arc volcanic rocks.Geochemical compositions of the diorite show double features of mantle and newly-formed crust,indicating that the diorite likely resulted from linear thermal uplift and thinning decompression of the crust under the effect of mantle flow diaperism in the early stage of subduction and collision.The mantle thermal energy and materials,together with partial melting of the crust,resulted in the formation the diorite in the post collision-extension environment during the ocean-continent transition of the Bangonghu-Nujiang suture zone.

关 键 词：冈底斯带西北缘 晚白垩世 闪长岩 LA-ICP-MS锆石U-PB测年 

分 类 号：P597.3[天文地球—地球化学] P588.122[天文地球—地质学]