Low-Ti gabbroic pluton in Dali, SW China: new evidence for back-arc lithospheric melting inducing early-stage magmatism of the Emeishan large igneous province

Abstract

The Emeishan large igneous province (LIP) was emplaced on the western Yangtze plate during the Permian and its formation is primarily attributed to a mantle plume. Recent research has shown that material from this plume modified the melts in the Palaeotethys subduction zone. However, it remains poorly understood whether, in turn, the subduction of Palaeotethys affected the formation of the Emeishan LIP. We report here geochronological, petrological, geochemical and isotopic studies of a gabbroic intrusion located in Jiangwei, in the Dali area of the Emeishan LIP. The gabbro has a weighted mean SHRIMP U–Pb age of c. 262 Ma. The key geochemical features include: depletion in Nb, Ta and Ti; enrichment in Th, U and Sr; low light to heavy rare earth element ratios; 87Sr/86Sr(t) values of c. 0.707; and εNd(t) values of c.−0.21. We conducted pMELTS thermodynamic modelling and batch-melting calculations to evaluate the origin and evolution of the gabbro based on real components of low-Ti picrites and xenoliths from the Yangtze lithosphere. Our results show that 3% melting of a hydrated spinel peridotite source from the Yangtze lithosphere can produce magma equivalent to the gabbroic intrusion. Integrating this conclusion with the tectonic background of the western Yangtze plate and the volcano-stratigraphic record of the Emeishan LIP, we infer that the early-stage magmatism of the Emeishan LIP was triggered by Palaeotethys back-arc extension with fluid modification from the subducting slab.Supplementary material: Tables S1–S7 are available at https://doi.org/10.6084/m9.figshare.c.5433267