Geochemistry and petrogenesis of the Permian metabasalts in the Jianglang dome, western Sichuan

A succession of bedded metabasalts occurs in the Permian strata in the Jianglang dome, western Sichuan. These rocks have well-defined pillow structures, and are composed mainly of hornblende (~80%), plagioclase (~15%) and minor quartz (< 3%) and magnetite (~2%). The results of research in this study have disclosed that the metabasalts are characterized by low SiO₂ (an average of 44.14%) and TiO₂ (an average of 1.79%), high ^TFe₂O₃ (an average of 13.95%) and MgO (an average of 11.64%); slightly right-leaning REE distribution patterns and unmarkedly Ce and Eu anomalies; enrichment of large ion lithophile elements Rb, Ba and U, and depletion of high field strength elements Nb, P, Zr and Hf; low La/Sm ratios (2.71-2.26),(Th/Ta)_PM ratios (1.36-1.14) and (La/Nb)_PM ratios (1.78-1.33). The above-mentioned results show that the Perian metabasalts in the Jianglang dome may be assigned to ocean-floor basalts, and remnants of palaeo-Tethyan oceanic crust. The magmas may be derived from the depleted mantle mixed with minor enriched mantle components, and were not contaminated with crustal matter during the ascending processes. Instead, they may be subjected to the crystallization differentiation of ilmenite. Compared with the Emeishan basalts, the metabasalts in the study area are not the products of the Late Permian Emeishan basaltic magma activities.