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    四川木里地区二叠纪苦橄岩和玄武岩成因及源区性质

    Petrogenesis and source characteristics of Permian picrites and basalts in Muli area, Sichuan Province

    • 摘要: 提要:前人对峨眉山玄武岩的研究已经取得大量的研究成果,但对于一些关键科学问题如岩浆源区组成、源区温压条件等还存在分歧,或有待进一步探讨。本文报道了四川木里地区二叠纪苦橄岩和相关玄武岩的岩石学、地球化学和Sr-Nd同位素特征,并进一步探讨了苦橄岩和相关玄武岩的岩浆源区性质、岩浆形成条件。研究表明:四川木里地区二叠纪火成岩主要岩石类型为苦橄岩、高钛玄武岩和低钛玄武岩;苦橄质岩浆来源于地幔柱头部中心的高温区域(地幔柱轴部),岩浆主要起源于石榴石稳定域;高钛和低钛玄武质岩浆来源于地幔柱尾部,高钛玄武质岩浆主要起源于石榴石稳定域,而低钛玄武质岩浆起源于石榴石稳定域和尖晶石稳定域的过渡带;苦橄质和玄武质岩浆在上升过程中都不同程度混染了大陆岩石圈地幔物质,其中低钛玄武质岩浆可能有少量地壳物质的混染。

       

      Abstract: Abstract:Nuremous papers have been published for Emeishan Permian basalts; nevertheless, some key scientific problem, such as magma source components and P-T conditions, remain problems of hot debate. This paper reported petrologic, geochemical and Sr-Nd isotopic data of the Permian picrites and related basalts in Muli area of eastern Sichuan, and discussed magma source characteristics and P-T conditions of these volcanic rocks. The authors have detected that main rock types are picrites and high-Ti and Low-Ti basalts. Picritic magmas were probably derived from the high temperature area at the center of the plume head (the axial zone of mantle plume) and melted within the garnet stable field. However, high-Ti and low-Ti basaltic magmas were probably derived from the mantle plume tail area. High-Ti basalts were mainly melted within the garnet stable field, but the low-Ti basalts were probably melted around the garnet-spinel transition. Both picritic and basaltic magmas were mixed with a subcontinental lithospheric mantle (SCLM) in various degrees during their upward migration, and the low-Ti basaltic magmas might have been contaminated by crust materials.

       

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