Primitive magmas in the Emeishan Large Igneous Province, southwestern China and northern Vietnam

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• 作者：Eero Hanski ; Vadim S. Kamenetsky ; Zhen-Yu Luo ; Yi-Gang Xu ; Dmitry V. Kuzmin
• 关键词：Picrite ; Komatiite ; Olivine ; Melt inclusion ; Permian ; Emeishan ; China
• 刊名：Lithos
• 出版年：2010
• 出版时间：September 2010
• 年：2010
• 卷：119
• 期：1-2
• 页码：75-90
• 全文大小：2296 K

文摘

There are several places in the Emeishan Large Igneous Province (ELIP) where highly magnesian volcanic or intrusive rocks accompany more abundant flood basalts. The high-Mg rocks vary in composition from LREE-depleted, low-Ti komatiites to LREE-enriched, high-Ti picrites. These magmas carried cognate olivine phenocrysts with Fo content higher than 91 mol % indicating that these olivines crystallized and equilibrated with high-Mg melts. The maximum measured Fo content from the Dali area is 93.5 mol % which, depending on the K_D value used, indicates a MgO content of 23–25 wt. % for the parental melt. The high estimated MgO wt. % values provide evidence for a hot portion of the Emeishan mantle-plume head with a potential mantle temperature of ca. 1700 °C. Melt inclusions trapped within olivine phenocrysts have compositions similar to those of the host lavas but with a higher variability in the abundance of incompatible trace elements. The inclusions yield a calculated maximum MgO content of ca. 22 wt. % for the melt. The compositional and isotopic variability of the high-Mg magmas in the ELIP is akin to that observed in basaltic rocks, which are divided into low-Ti and high-Ti types, suggesting that most of the basalts were developed in deep crustal magma chambers by fractional crystallization and mixing processes from primitive magmas.