峨眉山大火成岩省白马层状侵入体的成因  

Genesis of the Baima layered intrusion in the Emeishan Large Igneous Province

作　　者：汤庆艳 鲍坚 党永西 苏天宝 许仕海 TANG QingYan;BAO Jian;DANG YongXi;SU TianBao;XU ShiHai(Key Laboratory of Mineral Resources in Western China(Gansu Province),School of Earth Sciences,Lanzhou University,Lanzhou 730000 China)

机构地区：[1]兰州大学地质科学与矿产资源学院,甘肃省西部矿产资源重点实验室,兰州730000

出　　处：《岩石学报》2020年第7期2163-2176,共14页Acta Petrologica Sinica

基　　金：第二次青藏高原综合科学考察研究(2019QZKK0704);国家自然科学基金项目(41472070、41872073);甘肃省科技计划项目(18JR3RA266);兰州大学中央高校基本科研业务费专项资金资助项目(lzujbky-2017-77)联合资助。

摘　　要：峨眉山大火成岩省与二叠纪晚期的峨眉山地幔柱作用有关。白马层状侵入体是峨眉山大火成岩省赋存超大型Fe-Ti-V氧化物矿床的镁铁-超镁铁质侵入体之一。白马侵入体橄榄辉长岩和橄长岩全岩MgO与Cr、Ni的相关性表明白马母岩浆经历了较高程度的分离结晶作用。原始地幔标准化微量元素图解和球粒陨石标准化稀土元素图解总体具有显著的Sr、Eu和Ti正异常,Zr-Hf负异常;而Nb、Ta既有正异常,也有负异常,这些特征与岩石中磁铁矿、单斜辉石和斜长石等矿物的堆晶作用有关。(87Sr/86Sr)i=0.704232~0.704855,平均值为0.704706;εNd(t)=1.40~3.94,平均值为2.41。Sr-Nd同位素组成落于峨眉山苦橄岩和高钛玄武岩的范围内,混合模拟计算表明白马母岩浆经历了10%~30%硅质大理岩围岩的混染。因此,白马Fe-Ti-V氧化物矿床的形成受母岩浆的组成、分离结晶作用及大理岩围岩的混染等多种因素共同制约。Emeishan Large Igneous Province(LIP)is located in the western margin of the Yangtze Block,which is related to the Emeishan mantle plume in Late Permian.Several layered mafic-ultramafic intrusions host world-class Fe-Ti-V oxide ore deposits in this area.Baima layered intrusion is one of the mafic-ultramafic intrusions that host giant Fe-Ti-V oxide deposit in the Emeishan LIP.The close relationship of the whole-rock MgO contents with Cr and Ni concentrations in olivine gabbros and troctolites of the Baima intrusion indicate that its parental magma underwent extensive fractional crystallization.Primitive mantle-normalized trace elements and chondrite-normalized rare earth elements patterns of the samples from the Baima intrusion show positive Sr,Eu,and Ti anomalies,and negative Zr and Hf anomalies,and either positive or negative Nb and Ta anomalies,which is related to the accumulation of magnetite,clinopyroxene and plagioclase in the Baima intrusion.The(87Sr/86Sr)i ratios of the samples range from 0.704232 to 0.704855 with a mean value of 0.704706,and their εNd(t)values vary between 1.40 and 3.94 with an average value of 2.41.The Sr-Nd isotopes of the samples all fall in the ranges of Emeishan picrite and high-Ti basalts.The mixing calculation displays that the Baima parental magma had been contaminated by 10%~30%bulk assimilation of the siliceous marble country rocks.Therefore,the formation of the Baima Fe-Ti-V oxide deposit is controlled by many factors such as the compositions of the parental magma,fractional crystallization and the assimilation of the marble country rocks.

关 键 词：岩石成因 大理岩混染 白马侵入体 Fe-Ti-V氧化物矿床 峨眉山大火成岩省 

分 类 号：P588.125[天文地球—岩石学]