川西东风花岗岩及其闪长质包体成因对松潘−甘孜造山带三叠纪岩浆活动的启示  

Petrogenesis of the Dongfeng granite and its dioritic enclave:Implications for the Triassic magmatism in the Songpan−Ganzi Orogenic Belt.

作　　者：巫凌放 翟庆国[1] 胡培远[1] 唐跃[1] 刘一鸣 李金勇 杨宁 WU Lingfang;ZHAI Qingguo;HU Peiyuan;TANG Yue;LIU Yiming;LI Jinyong;YANG Ning(Institute of Geology,Chinese Academy of Geological Sciences/SinoProbe Laboratory,Beijing 100037,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]中国地质科学院地质研究所/自然资源部深地科学与探测技术实验室,北京100037 [2]北京大学地球物理与空间科学学院,北京100871

出　　处：《地质通报》2024年第12期2237-2255,共19页Geological Bulletin of China

基　　金：国家重点研发计划课题《西部伟晶岩型粘土型锂等稀有金属区域成矿背景》(编号:2021YFC2901901);中国地质科学院基本科研业务费项目《班公湖-怒江特提斯洋俯冲消减过程:以安多地区为例》(编号:JKYQN202308);中国地质调查局项目《羌塘盆地晚古生代地层沉积特征及石油地质条件调查评价》(编号:DD20242202)。

摘　　要：松潘−甘孜造山带已成为中国重要的锂多金属成矿带,多金属成矿作用与该地区晚三叠世—早侏罗世花岗质岩浆活动密切相关。岩浆演化的复杂过程导致了这些花岗岩的地球化学多样性。暗色包体在花岗岩的形成演化中扮演了重要角色,然而对于这些暗色包体在松潘−甘孜造山带花岗岩形成过程中的作用及对岩浆系统中Li的贡献目前知之甚少。东风岩体是松潘−甘孜造山带东部含有大量闪长质暗色包体的典型花岗岩体。锆石U−Pb定年结果显示,黑云母花岗岩和闪长质包体的结晶年龄分别为211.8±1.0 Ma和210.5±1.1 Ma。黑云母花岗岩具有富硅、过铝质,以及低Rb、Rb/Sr和Rb/Ba的特征,且具有明显富集的锆石ε_(Hf)(t)(−10.2~−5.9)、较高的初始Sr同位素组成((^(87)Sr/^(86)Sr)i=0.7117~0.7118)及富集的ε_(Nd)(t)(−9.7~−9.3),指示形成于中上地壳杂砂岩部分熔融。闪长质包体具有高Mg、Ca、Cr和Ni的特征,相对亏损的锆石Hf同位素(ε_(Hf)(t)=−9.6~−1.3)和全岩Nd同位素(ε_(Nd)(t)=−9.5~−8.8),以及低放射成因Sr同位素((^(87)Sr/^(86)Sr)i=0.7108~0.7113),指示起源于受软流圈地幔改造的下地壳源区。黑云母花岗岩斜长石斑晶和闪长质包体中斜长石斑晶从核部向边部An值急剧变化,揭示了长英质岩浆和镁铁质岩浆的混合作用。闪长质包体具有低的Li含量(26×10^(−6)~52×10^(−6)),反映松潘−甘孜造山带锂矿成矿物质与下地壳或更深部的地幔物质无关。The Songpan−Ganzi Orogenic Belt has emerged as a prominent Li−polymetallic metallogenic belt in China,characterized by polymetallic mineralization intricately associated with granitic magmatism during the Late Triassic to Early Jurassic period.The complicated magma evolution has resulted in the geochemical diversity of these granites.Enclaves play an important role in the formation of granite.However,it is still enigmatic about the role played by enclaves in the formation of granite within the Songpan−Ganzi Orogenic Belt,as well as their contribution to Li in the magmatic system.The Dongfeng pluton,located in the eastern part of the Songpan−Ganzi Orogenic Belt,is a typical granitoid that contains numerous enclaves.Zircon U−Pb dating yielded crystallization ages of 211.8±1.0 Ma for the biotite granite and 210.5±1.1 Ma for the dioritic enclave.The biotite granite is characterized by high−Si and prealuminous,alongside low Rb content,Rb/Sr and Rb/Ba ratios.Furthermore,it displays negative zirconε_(Hf)(t)values ranging from−10.2 to−5.9,notably high(^(87)Sr/^(86)Sr)i ratios between 0.7117 and 0.7118,and negativeε_(Nd)(t)values of−9.7 to−9.3.These features suggest that the parental magma derived from the partial melting of meta−sediments within the upper to middle crust.These dioritic enclaves display high concentrations of Mg,Ca,Cr and Ni,and relatively slightly depleted zircon Hf isotopes(ε_(Hf)(t)=−9.6 to−1.3)and whole−rock Nd isotopes(ε_(Nd)(t)=−9.5 to−8.8),as well as lower radiogenic Sr isotopes((^(87)Sr/^(86)Sr)i=0.7108~0.7113).This indicates a lower crustal source that had undergone modifications by asthenospheric mantle materials.The pronounced variations in An values from core to rim of the plagioclase phenocrysts from the biotite granite and dioritic enclaves provides compelling evidence for mixing process involving felsic and mafic magmas.The dioritic enclaves exhibit a low Li content(26×10^(−6)~52×10^(−6)),reflecting that the lithium deposits in the Songpan−Ganzi

关 键 词：松潘−甘孜造山带 晚三叠世—早侏罗世 强过铝质花岗岩 闪长质包体 锂成矿 

分 类 号：P595[天文地球—地球化学] P597.3[天文地球—地质学]