西藏南部南迦巴瓦地区变泥质岩和含石榴子石淡色花岗岩及其对构造事件的约束  

Metapelite and Garnet-Bearing Leucogranites in the Namche Barwa Area,Southern Xizang,and Their Constraints on Tectonic Events

作　　者：郝光明 曾令森[1] 赵令浩[2] 彭涛[3] HAO Guangming;ZENG Lingsen;ZHAO Linghao;PENG Tao(Beijing SHRIMP Center,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037;NationalResearch Center for Geoanalysis,Chinese Academy of Geological Sciences,Beijing 100037;Chengdu University ofTechnology,Chengdu,Sichuan 610059)

机构地区：[1]北京离子探针中心,中国地质科学院地质研究所,北京100037 [2]中国地质科学院国家地质实验测试中心,北京100037 [3]成都理工大学,四川成都610059

出　　处：《地质与勘探》2024年第4期643-660,共18页Geology and Exploration

基　　金：国家自然科学基金项目(编号:92055202、42172261);第二次青藏高原科学考察项目(编号:2019QZKK0702);中国地质调查局地质调查项目(编号:DD20221817、DD20221630)联合资助。

摘　　要：西藏南部南迦巴瓦地区位于喜马拉雅造山带的东端,该区保留了大量新生代变质和深熔作用记录,是研究喜马拉雅碰撞造山带演化过程的关键地区。本文在野外地质调查和室内显微岩石学观察基础上,通过锆石U-Pb年代学和全岩地球化学研究,分析南迦巴瓦地区变质岩和淡色花岗岩的年代学意义和地球化学特征。研究区露头可见含石榴子石淡色花岗岩平行片麻理侵入到变泥质岩中,该变泥质岩为含石榴子石的黑云斜长片麻岩,其继承锆石年龄为1617~565 Ma,还记录了28.1~16.4 Ma的新生代变质作用。含石榴子石淡色花岗岩形成于23.3±0.4 Ma,经历了18.4~8.6 Ma的岩浆事件,是南迦巴瓦地区构造减压过程中变质岩多次部分熔融的产物。该淡色花岗岩具有较高的SiO_(2)、K_(2)O、FeOT和铝饱和指数A/CNK,较低的Al_(2)O_(3)、CaO、Na_(2)O和Na_(2)O/K_(2)O,为过铝质富钾花岗岩。其富集Rb、K、Pb,亏损Ba、Sr、Nb、Ta、Nd、Zr、Ti,具有强烈的Eu负异常和海鸥状稀土分布模式,较高的Rb/Sr、Nb/Ta和较低的Zr/Hf,可能与发育大量的石榴子石并经历了较高程度的斜长石、独居石分离结晶作用和熔体结构改变有关。The Namche Barwa area of southern Xizang is located in the east of the Himalayan orogenic belt.This area has recorded extensive Cenozoic metamorphism and crustal anataxis,and is significant for studying the evolution process of the Himalayan orogenic belt.Based on field geological investigations and indoor microscopic petrological observations,this work analyzed the chronological significance and geochemical characteristics of metamorphic rocks and leucogranite in the Namche Barwa area through zircon U-Pb chronology and whole rock geochemistry.In this area,the garnet-bearing leucogranite parallel to schistosity intruded into metapelite in the outcrop.This metapelite is garnet-bearing biotite plagioclase gneiss,and its inherited zircon age ranges from 1617 Ma to 565 Ma,which recorded the Cenozoic metamorphism from 28.1 Ma to 16.4 Ma.The formation age of the garnet-bearing leucogranite is 23.3±0.4 Ma,and it experienced magmatic events from 18.4 Ma to 8.6 Ma.It is the product of multiple partial melting of metamorphic rocks during the tectonic decompression in the Namche Barwa area.This garnet-bearing leucogranite has higher SiO_(2),K_(2)O,FeOT and A/CNK,lower AL_(2)O_(3),CaO,Na_(2)O and Na_(2)O/K_(2)O,which belongs to peraluminous potassium rich granite.It is enriched in Rb,K,Pb,depleted in Ba,Sr,Nb,Ta,Nd,Zr,Ti,with strong depleted Eu and gull-like REE patterns,with higher Rb/Sr,Nb/Ta and lower Zr/Hf,which may be related to plagioclase and monazite separation crystallization and the melt structure transition.

关 键 词：喜马拉雅造山带 南迦巴瓦 变泥质岩 淡色花岗岩 深熔作用 西藏南部 

分 类 号：P618[天文地球—矿床学] P59[天文地球—地质学]