High-temperature melting of different crustal levels in the inner zone of the Emeishan large igneous province: Constraints from the Permian ferrosyenite and granite from the Panxi region

Abstract

The Late-Permian Emeishan mantle plume event caused large-scale flood basalts and related mafic-ultramafic layered mafic intrusions in the inner zone of the Emeishan large igneous province (ELIP). However, the related crustal magma response of this mantle plume event in the inner zone of the ELIP remains poorly understood. In this contribution, we report contemporaneous (~259 Ma) ferrosyenite and A-type 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 SiO2 (60.14 to 63.58 wt%), high Fe2O3T (4.28 to 8.52 wt%) and alkaline (Na2O + K2O = 10.91 to 12.75 wt%) contents. In combination with their positive zircon εHf(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 H2O-poor condition, which was induced by underplating of the high-temperature mantle plume. Rhyolite–MELTS modeling results show that ~7% melting of ferrodiorite-like source at ~1120 °C and 8 kbar can produce similar compositions with least evolved ferrosyenite under a relatively dry condition. The Baima granites have high SiO2 (70.58 to 74.26 wt%) contents and 10000*Ga/Al ratios (3.00 to 3.28), indicating the affinity to A-type granites. Their evolved zircon εHf(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 propose that the emplacement of ferrosyenitic magma resulted in low-degree partial melting at a relatively shallow crustal level, responsible for the formation of the A-type granites. In summary, this study highlights the significant impact on crustal magma response to the high-temperature mantle plume event in the inner zone of ELIP.