High-temperature melting of different crustal levels in the inner zone of the Emeishan large igneous province

Abstract

<p>Late-Permian intermediate-acid magmatic rocks in the Panxi region, inner zone of the Emeishan large igneous province (ELIP) is of great significance for deepening the magmatic process, crustal structure evolution and metal element mineralization under the background of mantle plume.In this contribution, we report contemporaneous (~259Ma) ferrosyenite and granite in the inner zone of the ELIP, and their chronological and geochemical data suggest simultaneous crustal melting at different depths. The ferrosyenites display moderate SiO<sub>2</sub>, high Fe<sub>2</sub>O<sub>3</sub>T and alkaline contents. In combination with their positive zircon ε<sub>Hf</sub>(t) values (+1.5 to +12.9), we propose that the ferrosyenites were formed by high temperature melting of Fe-rich refractory juvenile lower crust at H<sub>2</sub>O-poor condition, which was induced by underplating of the high-temperature mantle plume. Rhyolite–MELTS modelling results show that ~7% melting of ferrodiorite-like source at ~1120 ℃ and 8 kbar can produce similar compositions with least evolved ferrosyenite under a relatively dry condition. The granites have high SiO<sub>2</sub> contents and 10000*Ga/Al ratios, indicating the affinity to A-type granites. Their evolved zircon ε<sub>Hf</sub>(t) values (-8.1 to -0.6) indicate an evolved crustal source region. Rcrust modeling indicates that ~9% partial melting of ancient granodiorite-like crustal material under low pressure condition (4 kbar) can produce the observed granitic compositions. Considering the close spatial and temporal relationship between ferrosyenites and A-type granites, we highlight the significant impact on crustal magma response to the high-temperature mantle plume event in the inner zone of ELIP.</p>