鲁西地块济南辉长岩岩石学、地球化学和Os-Nd-Sr同位素研究  

Study on Petrology,Geochemistry and Os-Nd-Sr Isotopes of Jinan Gabbro in Luxi Block

作　　者：高林[1] 陈斌[2] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室,北京100871 [2]北京大学地球与空间科学学院,北京100871

出　　处：《地球科学与环境学报》2013年第2期19-31,共13页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(90914001;41121062)

摘　　要：对华北克拉通东部陆块鲁西地块济南辉长岩进行了详细的岩石学、地球化学和Os-Nd-Sr同位素研究,探讨了该岩体的成岩过程、地幔源区特征以及地壳混染在幔源岩浆演化过程中的作用。济南辉长岩在地球化学上富集轻稀土元素和大离子亲石元素,亏损重稀土元素以及高场强元素;它们具有高放射性成因的Os同位素组成,Sr-Nd同位素组成具有EM1型特征。岩石学和元素地球化学研究表明,该岩体在成岩过程中经历了显著的橄榄岩+辉石+斜长石的分离结晶。岩石学、地球化学和Sr-Nd同位素特征研究表明,济南辉长岩的母岩浆应该是含水的岩浆体系,且起源于一个古老的富集岩石圈地幔。岩体所具有的高放射性成因的初始Os同位素组成以及呈反相关关系的εNd(t)值和初始Sr同位素比值表明,其母岩浆在深部地壳位置侵位过程中遭受了古老的前寒武纪基性下地壳的混染。Petrology, geochemistry and Os-Nd-Sr isotopes of Jinan gabbro in Luxi block of eastern block of North China Craton were studied in detail, and diagenetic process, characteristic of mantle source and the role of crustal contamination on evolution process of mantle-derived magma were discussed. Jinan gabbro was rich in LREE and LILE, depleted in HREE and HFSE; radiogenic Os isotopic composition was high for Jinan gabbro, the characteristic of Sr-Nd isotopic composition was EMl-like. The results of petrology and element geochemistry suggested a significant fractional crystallization of olivine ＋ pyroxene ＋ plagioclase in forming the mafic pluton. The characteristics of petrology, geochemistry and Os-Nd-Sr isotopes showed that the parental magmas of Jinan gabbro was hydrous magma system, which originated from an old enriched lithospheric mantle. High radiogenic initial Os isotopic composition and inverse relationship between value of eNa and ratio of initial Sr isotopic compositions of the mafic pluton suggested that parental magmas were contaminated by Precambrian mafic lower crust duringmagma emplacement at a deep crustal level.

关 键 词：岩石学 地球化学 济南辉长岩 Os-Nd-Sr同位素 岩石成因 地壳混染 华北克拉通 

分 类 号：P581.1[天文地球—岩石学]