藏南亚东地区中新世岩浆活动及构造意义  

Miocene magmatic activity and tectonic implications in Yadong,southern Tibet

作　　者：王艳 高彭 尹常青 张健[2] 钱加慧 WANG Yan;GAO Peng;YIN ChangQing;ZHANG Jian;QIAN JiaHui(Guangdong Provincial Key Lab of Geological Processes and Mineral Resources,School of Earth Sciences and Engineering,Sun Yat-Sen University,Guangzhou 510275,China;Department of Earth Sciences,The University of Hong Kong,Hong Kong,China)

机构地区：[1]中山大学地球科学与工程学院,广东省地质过程与矿产资源探查重点实验室,广州510275 [2]香港大学地球科学系,中国香港

出　　处：《岩石学报》2024年第8期2353-2373,共21页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42325205、42373043、41973025、92155306、42025204)资助。

摘　　要：喜马拉雅淡色花岗岩是研究造山带构造-岩浆演化历史的岩石探针。亚东淡色花岗岩位于高喜马拉雅序列中部,其成因机制和构造意义有待进一步的研究和讨论。本研究提供了新的亚东地区淡色花岗岩和花岗片麻岩的全岩地球化学和锆石年代学数据。亚东淡色花岗岩具有相对较高的SiO_(2)、K_(2)O含量,和相对较低的CaO、FeO^(T)、MgO含量,属于过铝-强过铝质、高钾钙碱性花岗岩。它们具有较低的稀土含量,相对富集的LREE含量,明显的Eu负异常。这些地球化学特征同典型的高喜马拉雅淡色花岗岩极为一致。本研究获得了顶噶二云母花岗岩约23Ma和21Ma的两期结晶年龄,并且认为该地区高喜马拉雅结晶岩系的部分熔融可能早在36~30Ma就已经开始了。获得亚东淡色花岗岩的ε_(Nd)(t)值和(^(87)Sr/^(86)Sr)i分别为-16.7~-13.8和0.754080~0.791009,与亚东变沉积岩的Sr-Nd同位素组成极其一致,而花岗片麻岩具有明显更高的ε_(Nd)(t)值和(^(87)Sr/^(86)Sr)i,分别为-9.0~-8.8和0.847193~0.866306。因此,我们认为亚东淡色花岗岩源自高喜马拉雅结晶岩系中变沉积岩的部分熔融,且不含或极少有花岗片麻岩的物质贡献。综合全岩地球化学、变质岩石学及年代学研究,我们认为高喜马拉雅结晶岩系在埋藏加厚的过程中就已经发生了白云母为主的脱水部分熔融,在随后的伸展构造阶段发生大规模减压熔融,产生大量中新世淡色花岗岩。Himalayan leucogranites provide a natural probe to study tectonic-magmatic evolution history of continental collisional orogen.The Yadong leucogranites are located in the middle of the Higher Himalayan Sequence(HHS),and their petrogenesis and tectonic implications need to be further investigated and discussed.To address this issue,we carried out new whole-rock geochemistry and zircon geochronology study for leucogranites and granitic gneiss from Yadong area.The leucogranites are peraluminous and high-K calc-alkaline rocks,and characterized by high SiO_(2) and K_(2)O concentrations(69.4%~75.5%SiO_(2) and 2.88%~6.70%K_(2)O),but low CaO,FeO^(T),MgO concentrations(0.44%~1.74%CaO,0.29%~2.53%FeO^(T) and 0.04%~0.57%MgO),enriched LREE patterns and obviously negative Eu anomalies,which are consistent with typical High Himalayan leucogranites.LA-ICP-MS zircon U-Pb dating yields crystallization ages of ca.21.0Ma and 23.0Ma,and partial melting in Yadong may have started as early as 36~30Ma.Yadong leucogranites haveε_(Nd)(t)and(^(87)Sr/^(86)Sr)i values of-16.7 to-13.8 and 0.754080 to 0.791009,respectively,which are similar to those of metasedimentary rocks.The granitic gneisses have significantly higherε_(Nd)(t)and(^(87)Sr/^(86)Sr)i values of-9.0 to-8.8 and 0.847193 to 0.866306,respectively.These pieces of evidences indicate that the leucogranites were derived from partial melting of metasediments in the HHS without or with insignificant addition of granitic gneisses.Combining results from multidisciplinary studies including geochemistry,metamorphic petrology and geochronology,it is suggested that the dehydration melting of muscovite has already occurred during the burial and thickening of the HHS,and then large-scale decompression melting occurred during the tectonic extension stage,resulting in the large amounts of the Miocene leucogranites.

关 键 词：淡色花岗岩 亚东 U-PB年代学 SR-ND同位素 喜马拉雅 碰撞造山带 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]