滇西梁河三叠纪花岗岩的锆石微量元素、U-Pb和Hf同位素组成  

Trace Elements and Hf Isotope Compositions and U-Pb Age of Igneous Zircons from the Triassic Granite in Lianghe, Western Yunnan

作　　者：丛峰[1] 林仕良[1] 唐红峰[2] 谢韬[1] 李再会[1] 邹光富[1] 彭智敏[1] 梁婷[3] 

机构地区：[1]中国地质调查局成都地质调查中心,成都610081 [2]中国科学院地球化学研究所,贵阳550002 [3]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074

出　　处：《地质学报》2010年第8期1155-1164,共10页Acta Geologica Sinica

基　　金：云南1:5万梁河县;江东;帕底幅区域地质调查项目(编号1212010784007)资助的成果

摘　　要：在详细的区域地质调查基础上,分析了滇西梁河三叠纪花岗岩中锆石微区微量元素、U-Pb年龄和Hf同位素。花岗岩中大部分锆石具有振荡环带,为典型岩浆锆石,并发现独特的双核结构锆石,具有核幔边结构,双核锆石继承核与本文岩浆锆石有类似的微量元素特征,而双核锆石增生边(低轻稀土、轻微负Ce异常、高重稀土、低Th、高U、Ti、P)与它们不同。注意到双核锆石外围有一圈灰白色热液蚀变边,认为双核锆石增生边的微量元素特征可能是自身结晶生长过程和后期蚀变影响的综合结果,继承核和增生边同为岩浆成因。双核锆石继承核的206Pb/238U年龄分别为302.5±2.9Ma和289.9±2.5Ma,双核锆石增生边和其他岩浆锆石的206Pb/238U加全平均年龄为213.1±1.7Ma(MSWD=7.7),晚三叠世花岗岩的锆石具有负的εHf(213Ma)值(-9.6～-6.7),并且其tDM2Hf值(1.6～1.8Ga)远大于其结晶年龄,结合大地构造演化,认为花岗岩的形成可能与后碰撞伸展背景下古老地壳熔融相关。Based on detailed field survey, the trace element and Hf isotope compositions and U-Pb age of zircons from granite at Lianghe in Western Yunnan were studied. Most of the zircons exhibit magmatic oscillatory zoning, suggesting a typical magmatic origin. In particular, a zircon with two cores has been discovered, which preserved inherited core and growth zone and hydrothermal domain. The inherited cores show the similar trace element characteristics with igneous zircons. But the growth zone （with low LREE and negative Ce anomalies and high HREE, low Th, high U and Ti and P abundances） point to a significant difference from the magmatic zircons. The fact that the zircon with two cores was observed to have a significant hydrothermal domain, indicating that trace element characteristics of the growth zone might be the comprehensive result of the crystallization associated with hydrothermal activity. The inherited core and growth zone both have igneous affinity. Two inherited cores show the ^206Pb/^238U ages of 302.5±2.9 Ma and 289.9±2.5 Ma, respectively. Igneous zircons together with growth zone yielded a weighted mean ^206Pb/^238U age of 213.1±1.7 Ma （MSWD=7.7）, indicating the granites were formed in the late Triassic. Their εHf（213 Ma） are negative ranging from -9.6 to -6.7, with Hf model ages of 1.6-1.8 Ga higher than that of crystallization. Combined with the evolution of geotectonic, it is suggested that the granites were crust-derived magmas and maybe emplaced at a post-collision extensional setting.

关 键 词：滇西 梁河 花岗岩 锆石 微量元素 U-PB年龄 HF同位素 

分 类 号：P597.3[天文地球—地球化学]