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

• Published in: Lithos 2010-09, Vol.119 (1), p.75-90
• Main Authors: Hanski, Eero, Kamenetsky, Vadim S., Luo, Zhen-Yu, Xu, Yi-Gang, Kuzmin, Dmitry V.
• Format: Article
• Language: English
• Subjects: China; Emeishan; Komatiite; Melt inclusion; Olivine; Permian; Picrite
• ISSN: 0024-4937; 1872-6143
• DOI: 10.1016/j.lithos.2010.04.008

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.