西藏谢穷地区晚白垩世淡色花岗岩体和岩脉年龄及地球化学特征:对班公湖-怒江带后碰撞背景的制约  

Age and geochemical characteristics of Late Cretaceous leucogranites pluton and dykes in Xieqiong area,Tibet:constraints on the post-collisional setting of Bangong Co-Nujiang belt

作　　者：梁肖肖 高睿[1] 刘函[2] LIANG Xiaoxiao;GAO Rui;LIU Han(College of Earth Science,Chengdu University of Technology,Chengdu 610059,Sichuan,China;Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]中国地质调查局成都地质调查中心,四川成都610081

出　　处：《地质通报》2023年第1期92-106,共15页Geological Bulletin of China

基　　金：中国地质调查局项目《三江造山带昌都—澜沧地区区域地质调查》(编号:DD20211195)。

摘　　要：藏东左贡地块的晚白垩世侵入岩鲜有报道。对谢穷地区侵入于新元古界酉西岩群中的花岗岩体和岩脉进行了岩石学、地球化学及锆石U-Pb测年研究,揭示其岩石成因及形成环境。岩体岩石类型为含电气石白云母二长花岗岩,岩脉岩石类型为细粒花岗质岩脉,二者的LA-ICP-MS锆石U-Pb年龄分别为88.5±0.7 Ma和85.8±2.3 Ma,均侵位于晚白垩世。岩体与岩脉含白云母,无角闪石,均具有高硅(SiO_(2)=74.17%~78.88%)、富碱(K_(2)O+Na_(2) O=5.92%~9.00%)和富铝(Al_(2)O_(3)=12.61%~15.13%)的特点,铝饱和指数(A/CNK=1.11~1.40)和里特曼指数(δ<3.3),指示二者均属于过铝质钙碱性系列;均富集Rb、U、K、P和Pb,亏损Nb、Ti和Ba,具强烈的负Eu异常(δEu=0.18~0.56),表明为一套强过铝质亚碱性S型花岗岩,具有电气石型淡色花岗岩的特征。其可能为地壳缩短增厚挤压环境向地壳伸展环境转换过程中,构造减压导致的上地壳变质泥岩中含水矿物(白云母)脱水部分熔融的产物,为班公湖-怒江缝合带在东部的后碰撞演化过程提供了新的制约。The Late Cretaceous intrusive rocks in the Zuogong Block,eastern Tibet are rarely reported.This article reports on the granitic pluton and dykes invaded in the Neoproterozoic Youxi Group in the Xieqiong area,through petrology,geochemistry and zircon U-Pb chronology,to reveal its petrogenesis and formation environment.The granitic pluton type is tourmaline-bearing muscovite monzonitic granite,and the dike rock type is fine-grained granitic dike.The LA-ICP-MS zircon U-Pb ages of the two are 88.5±0.7 Ma and 85.8±2.3 Ma,respectively,both invaded in the Late Cretaceous.They contains minor muscovite,no hornblende.The granitic pluton and dike are characterized by high SiO_(2)(SiO_(2)=74.17%~78.88%),rich alkali(K_(2)O+Na_(2) O=5.92%~9.00%)and rich Al(Al_(2)O_(3)=12.61%~15.13%),A/CNK=1.11~1.40,Ritman indexδ<3.3,indicating that they belongs to the peraluminous calc-alkaline series;all are enriched in Rb,U,K,P and Pb elements and depleted in Nb,Ti and Ba elements;and strong negative Eu anomalies(δEu=0.18~0.56),which are indicative of peraluminous sub-alkaline S-type granite,and characteristics of a tourmaline-type leucogranite.It may be the product of dehydration and partial melting of water-bearing minerals(muscovite)in the upper crustal metamorphic mudstone caused by the transition from shortening and thickening extrusion environment to crustal extension environment.This result provides new constraints for the post-collision evolution process of the Bangong Co-Nujiang suture zone in the east.

关 键 词：西藏 晚白垩世 班公湖-怒江 淡色花岗岩 地质调查工程 地球化学 

分 类 号：P588.121[天文地球—岩石学] P595[天文地球—地质学]