Picrites from the Emeishan Large Igneous Province, SW China: A compositional continuum in primitive magmas and respective mantle sources

Flood basalts are one of remaining enigmas in global mantle petrology. They come in enormous quantities of up to 106 km3 of mantle-derived melts, and they erupt in rather short time intervals of only a few millions of years. Throughout geological history, all continents have been periodically flooded by dominantly basaltic and rare picritic magmas that can differ widely within the same province in terms of their major element (e.g. high- and low-Ti series), trace element, and radiogenic isotope compositions, suggesting significant compositional heterogeneity within the mantle source regions tapped. In this study of the Late Permian Emeishan large igneous province (ELIP) in SW China the unique picrite lavas from thick stratigraphic successions at the Binchuan and Yongsheng localities represent low-Ti and high-Ti classic‚ÄövÑvp endmembers of continental flood magmatism, respectively. The understanding of petrochemical variability of the Emeishan magmas, genetic links between different suites and their respective mantle sources employs deciphering chemical and physical compositions of their primary melts represented by homogenised melt inclusions hosted by exceptionally primitive olivine (up to 92 mol% Fo in both suites) and Cr-spinel (Cr# 64-72 mol% in Binchuan and 65-80 mol% in Yongsheng) phenocrysts. The average compositions of melt inclusions correspond to the melts that formed host lavas, however, their overall chemical variability and the presence of picrites in the province (e.g., Lijiang and Dali localities) with the compositions intermediate between low- and high-Ti endmembers advocates numerous parental melt batches that contributed to geochemicall diverse and more fractionated basaltic magmas of ELIP. The endmember and intermediate magma compositions are confirmed by the compostions of phenocrysts (Ni and Mn abundances in olivine, Ti abundances in Cr-spinel and clinopyroxene and trace element abundances in clinopyroxene). The endmember melt and phenocryst compositions (e.g., Gd/Yb in rocks, melt inclusions and clinopyroxene and Ni-Mn systematics in olivine) define a peridotite and garnet pyroxenite mantle sources for the low- and high-Ti endmembers, respectively. The Sr and Nd isotopic compositions of the two endmember magmas are similar (87Sr/86Sri ~0.7045; ˜í¬µNd(t) ~+1.7) and more representative of the source in the subcontinental lithospheric mantle than the convective asthenoshpere or or deep mantle plumes‚ÄövÑvp.