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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.
Recent research on the petrology, geochemistry and genetic mineralogy of the ultramafic rocks has been found in the Zaohuo area in the northern part of the East Kunlun, Qinghai Province.The rocks are mainly composed of clinopyroxene, orthopyroxene and amphibole, A small amount of plagioclase, quartz, biotite and iron opaque minerals, amphibole and biotite are retrograded metamorphic minerals.The genetic analysis of orthopyroxene is magmatic origin, so the ultramafic rocks are pyroxene Non-granulite.The chemical composition of the pyroxene is characterized by anomalous high MgO, high CaO and low Al2O3, and the trace elements are characterized by Rb, Th enrichment and depletion of Nb and Ti, indicating that they originate from enriched mantle. According to the characteristics of lithofacies and rare earth elements, the pyroxenite is believed to be pyroxene magma generated from the partial melting of the subducted oceanic crust and mantle peridotite, and then to the crust The central part is formed by cooling and crystallization, and the geology of the field shows that the emplacement of pyroxene is later than the occurrence of mylonitization of the surrounding rock, ie, later than the formation of the surrounding rock, that is, the Early Permian, indicating that the pyroxene is in Permian paleontitis ocean north large-scale Backlash arc and the resulting structure is formed extending background.