矿床地球化学国家重点实验室知识库

The Triassic post-Emeishan large igneous province (ELIP) basalts, mainly found in the Kaiyuan (KY), Qilinshan (QLS), and Laochang–Kafang (LK) areas, show spatial and geochemical relationships with the Permian ELIP, SW China. Specifically, the post-ELIP basalts are located in the southern part of the intermediate zone of the ELIP. These basalts have major trace element and Sr–Nd isotope features that are similar to those of Permian Emeishan high-Ti basalts. The LA-ICP-MS zircon U–Pb age and whole-rock platinum-group elements (PGE) concentrations of the post-ELIP basalts are reported in this paper. The determined age of 247.7 ± 1.4 Ma for the KY volcanic rocks is almost 10 Ma younger than the termination age of the ELIP magmatism, supporting their origin from post-ELIP magmatism. All the post-ELIP basalts show uniform but significant low PGE contents. Ir and Ru are depleted relative to Rh, Pt, and Pd in the primitive mantle-normalized PGE patterns, suggesting that a low degree of partial melting of the mantle source plays an important role in the PGE characteristics of the post-ELIP basalts. The Ir and Ru contents of the post-ELIP basalts are similar to those of the Emeishan high-Ti basalts. However, the Pt and Pd contents are strikingly depleted. This is consistent with the notion of early extraction of palladium-group PGE during the eruption of the Emeishan basalts.