云南大平糜棱岩化碱性花岗岩的锆石特征及其地质意义  

Characteristics of Zircons for Dating from Daping Mylonitized Alkaline Granite in Yunnan and Their Geologic Implications

作　　者：张玉泉[1] 夏斌[1] 梁华英[1] 刘红英[1] 林清茶[1] 

机构地区：[1]中国科学院广州地球化学研究所边缘海地质重点实验室,广州510640

出　　处：《高校地质学报》2004年第3期378-384,共7页Geological Journal of China Universities

基　　金：中国科学院知识创新工程重要方向性项目 (KZCX2 -SW - 117;KZCX2 - 10 1)

摘　　要：在哀牢山—金沙江新生代钾质碱性岩浆岩带的南端 ,云南金平县大平糜棱岩化钠闪石霓石花岗岩中锆石 ,主要为“变质锆石”和具有老核新壳的“变质复合型锆石” ,它们皆具不规则状和圆化的外形 ,并常高度的富集成堆和显示有一定层位。用ELA ICP MS和SHRIMP对锆石定年 ,结果表明 ,变质复合型锆石中老核年龄为 2 4 7.9± 6 .4Ma ,新壳和变质锆石年龄为 14 5 .7± 3.4Ma。薄片观察发现 ,在岩体发生糜棱岩化之前还有一次区域变质作用 ,呈现在糜棱岩化弱的地段岩石发育柱粒变晶结构和花岗变晶结构 ,而且残留有清楚的层理 。The Daping mylonitized riebeckite-aegirine granite is located in the southern part of the Ailaoshan-Jinshajiang Cenozoic alkaline magmatic rock belt. The zircons for dating form this granite are of two types: the metamorphic zircons and the metamorphic composite zircons which have old cores and new shells. Their crystal morphology is irregular and/or rounded. The high-degree concentration and layering of zircons are observed in rock thin sections. The results of dating are as following: the old core U-Th-Pb age is 247 Ma by using ELA-ICP-MS and the new shell U-Pb age is 145 Ma by using SHRIMP in metamorphic composite zircons. At the same time, there was a regional metamorphic process before mylonitization. In the weakly mylonitized segments the rocks have prism-granular blastic texture and granoblastic texture. The rocks have clear layering, which suggests a sedimentary-metamorphic genesis of this granite.

关 键 词：ELA-ICP-MS和SHRIMP年龄 锆石 碱性花岗岩 云南省金平县 

分 类 号：P57[天文地球—矿物学]