Permian, rifting related fayalite syenite in the Panxi region, SW China

Abstract

Within the Panxi rift of the Permian Emeishan large igneous province (ELIP), SW China, a 20 km2 quartz-bearing fayalite syenitic pluton intrudes the 260 Ma Baima igneous complex (BIC). The fayalite syenite is dated using SHRIMP zircon U-Pb techniques at 252 ± 2.5 Ma. The Panxi fayalite syenite is mainly composed of alkali feldspar, ferroan augite, fayalite, quartz and Fe-Ti oxides and contains 61.8-63.7 wt.% SiO2, 5.0-7.3 wt.% Fe2O3t and 9.9-12.1 wt.% total alkalis, belonging to an A-type variety of ferroan alkalic metaluminous granitoids. The fayalite syenite displays positive Eu anomalies (Eu/Eu* = 0.9-8.9) and is enriched in LREE [(La/Yb)N =6.6-11.5]. The e{open}Nd values and (87Sr/86Sr)initial ratios of the fayalite syenite range from + 1.3 to + 1.9 and from 0.7035 to 0.7068, respectively. The fayalite syenite and the BIC had the same mantle source; however the 8 myr age gap between them suggests the fayalite syenite formed by remelting of underplated mafic magmas injected into the crust during ELIP magmatism. The ages of the fayalite syenite and BIC are coincident with two Permian mass extinction events and suggest that ELIP may have influenced both. © 2007 Elsevier B.V. All rights reserved.