今天是2018年12月11日

张广才岭地块早-中二叠世镁铁质侵入岩体的年代学、地球化学及岩石成因

DOI:10.3799/dqkx.2018.721

作者:冯光英,刘燊,牛晓露,杨经绥

联系地址:地幔研究中心,国土资源部深地动力学重点实验室,中国地质科学院地质研究所,北京 100037

摘要:双凤山基性侵入岩体位于松嫩-张广才岭地块南缘,其岩石组成主要为橄榄辉长岩.锆石LA-ICP-MS U-Pb定年显示该岩体形成于279±4 Ma.岩石矿物组成主要为橄榄石、单斜辉石、斜方辉石、高An值(80.1~87.9)斜长石以及以反应边形式存在的角闪石,矿物学特征指示其母岩浆为经历过充分流体交代的富水岩浆.全岩主微量元素组成揭示其源区物质组成为石榴子石二辉橄榄岩,部分熔融程度约20%,岩浆演化过程中经历了斜长石堆晶作用以及斜方辉石的结晶分异作用.全岩Sr-Nd同位素及锆石Hf同位素研究显示其( 87Sr/ 86Sr )i=0.705 185~0.706 089,并具有正的 ε Nd ( t )值(0.9~1.3)和 ε Hf( t )值(0~10.2),表明其来源于亏损的地幔源区,并且岩浆上升过程中没有经历明显的地壳混染.微量元素和同位素特征综合反映岩浆源区经历了古亚洲洋俯冲沉积物熔体和流体交代作用的改造,但起主导作用的是流体.其地球化学特征总体显示MORB以及弧型玄武岩过渡的特征,暗示其形成于弧后伸展环境.研究区基性侵入岩地幔源区的不均一性主要受到古亚洲洋多期次俯冲作用析出熔/流体对上覆地幔楔不同程度的改造.

关键字:早-中二叠世;松嫩-张广才岭地块;镁铁质侵入岩;岩石成因;地球化学

Geochronology, Geochemistry and Petrogenesis of Early-Middle Permian Mafic Intrusion in Zhangguangcai Range, China

Author:Feng Guangying, Liu Shen, Niu Xiaolu, Yang Jingsui

Author Address:Cenler for Advanced Research on the Mantle (CARMA), Key Laboratory of Deep-Earth Dynamics of Ministry of Land and Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

Abstract:The Shuangfengshan mafic intrusion crops out in the southern margin of the Songnen-Zhangguangcai range. It is predominantly made of olivine gabbro, which yielded a crystallization age of 279±4 Ma (Early-Middle Permian). These rocks consist mainly of olivine, pyroxene, high-An (80.1-87.9) plagioclase and hornblende as reaction rim. The features of these minerals indicate a high-H2O or water-saturated parental magma which experienced fluid metasomatism in the mantle source. Major and trace elements studies suggest that the mafic magma was derived from partial melting (~20 %) of depleted garnetlherzolite mantle source. Variable degrees of plagioclase accumulation and orthopyroxene crystal fractionation occurred in the process of magma evolution. They are also characterized by relatively low Sr isotopic ratio (0.705 185-0.706 089), positive ε Nd ( t ) (0.9-1.3) and ε Hf( t ) (0-10.2) values, confirming that the Shuangfengshan mafic magma was derived from depleted mantle source and apparent crustal contamination was not found during magma upwelling. Combining trace elemental and isotopic results suggest that the parental magmas were likely derived from mantle wedge metasomatized by sedimentary melt and fluid from the subducted Paleo-Asian slab. Moreover, these rocks display transitional properties of MORB and arc basalt, conforming that the studied olivine gabbros were probably formed in back-arc extensional environment. And the mantle heterogeneity beneath the studied area was probably reduced by the multi-stage Paleozoic subduction of the Paleo-Asian Ocean.

Keyword:Early-Middle Permian; Songnen-Zhangguangcai range; mafic intrusion; petrogenesis; geochemistry

 

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作者简介:冯光英(1983-),女,副研究员,博士,从事岩浆岩及地幔橄榄岩岩石学与地球化学研究.ORCID: 0000-0002-2399-375X.E-mail: fengguangying198@163.com

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