藏南白朗地区宗卓组混杂岩的物质来源和形成时代——来自岩石学和碎屑锆石U-Pb定年的证据  

Ages and Provenance of the Zongzhuo Formation of Melanges in Bailang Area,Southern Xizang(Tibet):Evidence from Petrology and Detratal Zircon U-Pb Geochronology

作　　者：程俊 石卫刚 张文峰 郭俊 翟杰 米玛旺久 

机构地区：[1]陕西区域地质矿产研究院,陕西咸阳712000 [2]西藏地勘局第二地质调查大队,拉萨850003

出　　处：《地质论评》2017年第6期1440-1450,共11页Geological Review

基　　金：中国地质调查局青藏专项冈底斯成矿带地质矿产调查计划项目(编号:1212011221060)的成果~~

摘　　要：本文通过对藏南白朗地区宗卓组混杂岩"基质"进行岩石学、碎屑锆石形态学和U-Pb同位素测年等研究,结果表明:"基质"中碎屑岩岩屑成分以中酸性熔岩为主,石英颗粒在阴极发光下主要呈不发光或弱发光,为低温变质成因的自生石英再沉积;碎屑锆石以岩浆成因锆石为主,少量变质成因锆石,多因经历了一定距离的搬运磨蚀作用而呈浑圆状、椭圆状;碎屑锆石年龄绝大多数分布于422~2867 Ma(43.5%)和71~205 Ma(52.2%),在中元古代(1032~1569 Ma)和早白垩世(102~142 Ma)形成两个年龄主峰。综合研究将研究区宗卓组混杂岩中"基质"的形成时代限定为晚白垩统马斯特里赫特期,雅鲁藏布江缝合带北侧冈底斯弧与南侧印度大陆北缘均对其物源具有一定的贡献。Objectives：The Upper Cretaceous Zongzhuo Farmation in southern Xizang（Tibet） is located on the south side of the Yarlung Zangbo suture zone. Academics believe that it should belong to sedimentary mélange,and has always been attracting the attention of the scholars both at home and abroad. Until now, geologists have usually been studying configuration, material sources of the rock block, in order to study formation mechanism but neglected the “matrix”. Therefore, the rock thin section and detratal zircon from the Zongzhuo Formation in Bailang area had been collected to analyze the formation timing and provenance by author. Methods：The cathodoluminescence technique and the detratal zircon U Pb ages were used to determine the provenance of the “matrix” from the Zongzhuo Farmation.The cathodoluminescence image of sandstone sample and the detratal zircon U Pb analysis were carried by State key laboratory of continental dynamics at Northweatern University. Results： he ages of the detrital zircons are nearly all between 422～2867Ma（43.5%） and 71～205Ma（52.2%）. Conclusions：The rock debris of the sandstones in the “matrix” are mainly intermediate—acid volcanic rock; Quartz should come from ancient sedimentary rock, because they have no light by cathodoluminescence; Most of the detrital zircons that belong to magmatic zircons look like circle after transportation and abrasion; The comprehensive evaluation showed that the deposition time of the Zongzhuo Formation is limited to Maastrichtian because the youngest U Pb age was 71±2Ma; the provenance were from the volcanic—magma arc belts of Gangdisi and the northern margin of the Indian Continent.

关 键 词：藏南 宗卓组 混杂岩 碎屑锆石 物源 锆石U-Ph定年 

分 类 号：P581[天文地球—岩石学] P597.3[天文地球—地质学]