内蒙古中部二叠纪额布图岩体的橄榄石成分特征及其对辉石岩地幔源区的指示  

Compositions of Olivine of Permian Erbutu Ultramafic Intrusion in the Central Asian Orogenic Belt(Inner Mongolia):Insights for the Pyroxenite Mantle Source

作　　者：暴宏天 王焰[1,3] 曹勇华 魏博 BAO Hongtian;WANG Christina Yan;CAO Yonghua;WEI Bo(Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China;Guangdong Provincial Key Laboratory of Mineral Physics and Materials,Guangzhou 510640,Guangdong,China)

机构地区：[1]中国科学院广州地球化学研究所,矿物学与成矿学重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]广东省矿物物理与材料研究开发重点实验室,广东广州510640

出　　处：《大地构造与成矿学》2021年第6期1185-1201,共17页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41730423、41902077)资助。

摘　　要：内蒙古中部的额布图超镁铁质岩体位于中亚造山带与华北克拉通北缘的碰撞拼贴带内,发育铜镍硫化物矿化。该岩体主要由橄榄斜方辉石岩和斜方辉石岩组成,橄榄斜方辉石岩中橄榄石含量~15%,斜方辉石岩中橄榄石含量<5%,两种岩石中橄榄石的Fo值介于83~87之间。在Fo值相同时,与橄榄岩地幔部分熔融熔体中结晶的橄榄石相比,额布图岩体中的橄榄石具有较低的Mn含量,指示其母岩浆可能不是橄榄岩地幔的熔融产物。同时,该岩体的橄榄石具有较低的Mn/Zn和Mn/Fe值、较高的Zn/Fe值,与来源于典型辉石岩地幔的Mwenezi和Tuli玄武岩中橄榄石斑晶的相应比值一致。因此,额布图岩体的地幔源区可能以辉石岩为主。同时,该岩体中橄榄石的Ca含量较低、Li含量较高指示其源区可能经历了俯冲流体的改造。因此,额布图岩体地幔源区中的辉石岩组分可能是当古亚洲洋板片向南俯冲至华北克拉通之下时,来自俯冲板片的流体/挥发分进入上覆地幔楔,造成先存于地幔中的古老下地壳组分发生熔融并交代周围的地幔橄榄岩形成的。The Erbutu ultramafic intrusion is located in the suture zone between the Central Asian Orogenic Belt and the northern margin of the North China Craton(NCC).The intrusion contains Ni-Cu sulfide mineralization.The intrusion is mainly composed of orthopyroxenite and olivine orthopyroxenite,both of which contain olivine that has Fo contents ranging from 83 to 87.At given Fo contents,the olivine in the rocks of the Erbutu intrusion has much lower Mn than that of the olivine crystallized from the magma derived from the peridotite mantle,indicating that the parental magma of the Erbutu intrusion was unlikely derived from a peridotite mantle.The olivine in the rocks of the Erbutu intrusion has Mn/Zn,Mn/Fe and Zn/Fe ratios similar to those of the olivine in the Mwenezi and Tuli basalts that were derived from typical pyroxenite mantle.Therefore,the Erbutu intrusion is likely derived from a pyroxenite dominated mantle source.The olivine in the rocks of the Erbutu intrusion contains lower Ca but higher Li than that of the olivine in igneous rocks in intra-plate settings,indicating that the mantle source of the intrusion may have been metasomatized by slab-derived fluids.It is proposed that during the subduction of the paleo-Asian oceanic slab beneath the northern margin of the NCC,slab-derived fluids were released and added to the mantle wedge and triggered melting of ancient lower crustal materials(e.g.,eclogite)in the mantle,the melt of the eclogite was then reacted with the ambient mantle peridotite and produced the pyroxenite component in the mantle.

关 键 词：橄榄石 辉石岩地幔 额布图超镁铁质岩体 中亚造山带 

分 类 号：P595[天文地球—地球化学]