滇西勐养花岗岩体暗色包体的地球化学特征及成因  

Geochemical characteristics and genesis of the mafic enclaves in Mengyang intrusion in the Tengchong block, western Yunnan

作　　者：邹光富[1] 毛琼[2] 丛峰[1] 林仕良[1] 李再会[1] 高永娟[1] 

机构地区：[1]成都地质矿产研究所,四川成都610082 [2]华北油田勘探开发研究院,河北任丘062552

出　　处：《中国地质》2016年第2期419-431,共13页Geology in China

基　　金：中国地质调查局"云南1:5万梁河县;江东;帕底幅区域地质调查项目"(1212010784007)资助~~

摘　　要：勐养侵入岩体主要由黑云母二长花岗岩（128 Ma）、花岗闪长岩（113 Ma）和辉长质（123 Ma）、闪长质包体（120Ma）组成。暗色包体主要分布在花岗闪长岩中,包体岩性主要为辉长岩包体和闪长岩包体。包体具有岩浆结构,部分包体具有塑性流变特征,有些包体具有淬冷边和反向脉,包体中可见针状磷灰石,表现出岩浆混合的岩相学特征。岩石地球化学特征研究表明,寄主岩石与暗色包体同为准铝质-过铝质、钙碱性-高钾钙碱性系列岩石。寄主岩石与暗色包体的的稀土配分曲线模式和微量元素原始地幔标准化蛛网图形态基本一致,为岩浆混合作用的结果。所有样品均富集大离子亲石元素（如Rb、Th、U和Nd）、亏损高场强元素（如Nb、Ta、Ce和Zr）。勐养早白垩世侵入岩形成于岩浆弧环境。暗色包体具有低的Si O2含量（Si O2为48.02%和59.8%）和高的Mg#值（Mg#=48.1-68.5）,表明暗色包体的原生岩浆应是板块俯冲带流体交代地幔橄榄岩的部分熔融的产物,并受后期岩浆混合作用的改造。暗色包体锆石的εHf（t）为3.6-6.2,Nb/Ta值为12.1-15.4,显示岩浆源区具有亏损地幔特征。黑云二长花岗岩的Mg#=33.5,Nb/Ta值为10.9,表明岩浆主要来源于古老的地壳物质的部分熔融。花岗闪长岩锆石的Mg#=44,Nb/Ta值为12.5,岩浆主要来源于地幔和地壳,为黑云二长花岗岩与幔源岩浆混合作用的产物。腾冲地块早白垩世勐养侵入岩体及其暗色包体的的成因,是左贡—保山板块洋壳向南西俯冲在波密—腾冲地块之下,使区域地壳不断加厚并导致区域重力均衡隆升,深部地壳物质在加热后抬升减压过程中发生部分熔融,形成大量的花岗岩浆。由于俯冲洋壳板块在俯冲、碰撞过程中诱导的幔源岩浆与重熔物质发生岩浆混合作用,形成花岗闪长岩和暗色包体。Located in Mengyang area of the Tengchong block in western Yunnan, the Mengyang intrusion consists of biotite monzogranite（128 Ma） and granodiorite（113 Ma） with abundant gabbroic enclaves（123 Ma） and dioritic enclaves（120 Ma）. The darkenclaves, which are mainly gabbroic enclaves and dioritic enclaves, are mainly distributed in the granodiorite. The dark enclaves have igneous texture, and some of them are characterized by plastic flow deformation, quenching boundary, reverse pulse and acicular apatite, suggesting petrographic characteristics of magma mixing. Geochemical data show that the host granitoids and mafic enclaves are all metaluminous to peraluminous and high-K calc-alkaline enclaves enriched in LILE（ such as Rb,Th,U, Nd and Pb） and depleted in HFSE（ such as Nb,Ta,Sr,Zr）. The host rock and dark enclaves are metaluminous, calc-alkaline and high-K calc- alkaline series rocks. Geochemical data show that the host granitoids and mafic enclaves are all metaluminous to peraluminous, calc-alkaline and high-K calc-alkaline series rocks enriched in LILE（ such as Rb,Th,U, Nd and Pb） and depleted in HFSE（ such as Nb,Ta,Sr,Zr）. The REE patterns and primitive mantle normalized trace element spider diagrams of the host rock and dark enclaves are nearly of the same shape,which indicates that they have a close relationship in magma mixing. The Early Cretaceous granitoids are considered to be of the volcanic island arc tectonic setting. The gabbroic enclaves and dioritic enclaves are characterized by low Si O2, high Mg O, high K2 O and high Mg#（Mg#= 48.1-68.5）. Zircon in the dioritic enclaves has εHf（122 Ma）values of 3.6-6.2, TDM1 Hf ratios of 535-665 Ma, and Nb/Ta ratios of 12.1-15.4, suggesting that the dioritic enclaves had the nature of mantle derived magmas, and that mafic magma was directly derived from depleted mantle source region and was subjected to magma mixing in late reformation. The Mg#value of biotite monzogranite is 33.5, and Nb/Ta ratio is 10.9. The Mg#value of gran

关 键 词：花岗岩类 暗色包体 岩浆混合 腾冲地块 滇西 

分 类 号：P588.121[天文地球—岩石学]