今天是2017年11月21日

东昆仑中灶火地区超镁铁质辉石岩的成因

DOI:10.3799/dqkx.2013.119

作者:罗文行,钱莉莉,李德威,朱云海,刘德民,高成

联系地址:长江三峡勘测研究院有限公司,湖北武汉

摘要:最近在青海东昆北中灶火地区发现超镁铁质岩的岩石学、地球化学以及成因矿物学等方面的研究成果.岩石主要由单斜辉石、斜方辉石和角闪石组成,另有少量斜长石、石英、黑云母和铁质不透明矿物.角闪石和黑云母为后期退变质矿物.斜方辉石成因判别分析结果为岩浆成因,故该超镁铁质岩为辉石岩而非麻粒岩.该辉石岩化学成分上表现为异常的高MgO、高CaO、低Al2O3特征,微量元素表现为Rb、Th富集而Nb、Ti的亏损,表明其来源于富集地幔.通过岩相学、稀土元素等特征与前人研究结果对比认为该辉石岩是俯冲洋壳部分熔融产生的富Si熔体与地幔橄榄岩发生交代反应产生辉石岩岩浆,然后底侵到地壳中部冷却结晶形成的.野外地质特征显示辉石岩的侵位晚于发生糜棱岩化的围岩,即晚于围岩的形成时代,即早二叠世,说明该辉石岩是在中二叠世古特提斯洋向北大规模俯冲及其所导致的弧后伸展的构造背景下形成的.

关键字:辉石岩;地球化学;矿物学;交代成因;东昆仑

Petrogenesis of the Zhongzaohuo Ultramafic Pyroxenite Pluton, East Kunlun:Constraints from Petrology, Geochemistry and Genetic Mineralogy

Author:LUO Wenxing, QIAN Lili, LI Dewei, ZHU Yunhai, LIU Demin, GAO Cheng

Author Address:Three Gorges Geotechnical Consultants Co., Ltd, Wuhan

Abstract:A ultramafic pyroxenite pluton has been discovered in Zhongzaohuo area in the East Kunlun orogen Recently. This paper reports the results of petrological, geochemical and genetic mineralogy research on the pyroxenite pluton. The rock is mainly composed of clinopyroxene, orthopyroxene and amphibole, and minor plagioclase, quartz, biotite and iron opaque minerals. Amphibole and biotite were formed during retrograde metamorphism. The discriminant analysis results suggest that the Opx are magmatogenic, thus the rock should be named pyroxenite rather than granulite. The rock has high MgO, CaO and low Al2O3 and enriched in Rb and Th and depleted in Nb and Ti, showing clear evidence for an enriched mantle source. Field occurrence of the pyroxenite pluton suggests that the pyroxenite pluton was formed after the mylonization of the surrounding rocks. Combined with the tectonic evolution of East Kunlun, we come to the conclusion that the subduction of an Paleo-Tethys(Anyemaqen) oceanic slab at the Middle Permian led to fluid and Si-rich?melt metasomatism, inducing partial melting of an enriched lithospheric mantle(peridotites) to form the ultramafic pyroxenite magma. The pyroxenite magma underplated the overlying lower crust, captured the metamorphic zircons of the granulite and exchanged some trace elements, but didnt result in the lower crust partial melting to form any felsic magma. The pyroxenite magma emplaced alone eventually.

Keyword:pyroxenite; geochemistry; mineralogy; metasomatic; the East Kunlun

 

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作者简介:罗文行(1983-),博士,主要从事大陆构造地质勘查与研究工作.Email: lwx1983@gmail.com

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