Silicic magmas from the Emeishan large igneous province, Southwest China: Petrogenesis and their link with the end-Guadalupian biological crisis

Abstract

The Emeishan large igneous province in SW China comprises a bimodal mafic–silicic suite with the silicic rocks occurring at the uppermost part of the thick lava sequence. The silicic rocks have an age of 257–263 Ma, and are thus roughly coeval with the Guadalupian–Loping (G–L) boundary event. Most silicic rocks (trachyte and rhyolite) from the Emeishan province have rather uniform ε Nd values (+ 1 to + 2.9) that are comparable with the uncontaminated high-Ti basalts. This fact and the remarkably narrow ranges of incompatible element ratios (e.g., Zr/Nb) of the basalt–silicic suite indicate a genetic relationship between basalt and silicic members. The significant difference between the Emeishan rocks and the experimental melts of hydrated basaltic crust, suggests the fractional crystallization of basaltic magma, rather than crustal melting, as the major petrogenetic process for the formation of silicic rocks. Indeed, their major and trace element trends can be modeled by fractionation of the observed mineral phases (feldspar, clinopyroxene, Fe–Ti oxide and apatite). In contrast to the virtually closed system differentiation processes associated with trachytes, the rhyolites may have experienced interaction with upper crustal material during ascent. The geochemical characteristics and recent assessment of timing of the Emeishan volcanism suggest the Emeishan rhyolites as the potential source of the widespread clay bed at the G–L boundary in south China. This enhanced the causal link between the Emeishan eruption and the end-Guadalupian biological crisis.