Petrogenesis and Geological Implications of the Qiaoqi Intrusion in Western Margin of the Yangtze Block, SW China: Evidence from Geochronology, Geochemistry, and Hf Isotopes

Late Permian-Early Triassic basic rocks, which are widespread in the western margin of the Yangtze block (SW China), provide critical information for regional tectonic evolution. The Qiaoqi intrusion, distributed in the western margin of the Yangtze block, is selected as a representative for discussion in this paper. LA-ICP-MS zircon U-Pb dating results show that the Qiaoqi intrusion was formed at 245 +/- 1 Ma. It belongs to the medium-K calc-alkaline and tholeiitic basalt series. It is characterized by high concentrations of Fe2O3T (11.53 wt. % to 15.50 wt. %), TiO2 (1.81 wt. % to 3.20 wt. %), Al2O3 (11.80 wt. % to 15.60 wt. %), and low concentrations of MgO (4.51 wt. % to 8.93 wt. %). The LREE and LILE (such as Cs, Rb, Ba and Th) are enriched, with insignificant Eu anomalies (Eu/Eu* = 0.92 to 1.13). The chondrite-normalized REE distribution diagram shows a right-leaning pattern, similar to ocean island basalts (OIB), displaying the geochemical characteristics of enriched mantle sources. The zircon epsilon Hf(t) values are relatively high (+12.7 to +15.5) and the single-stage Hf model ages are relatively young (tDM = 272 to 386 Ma). Modeling further reveals that the parent magma was derived from 13% to 19% partial melting of garnet peridotite. Comprehensive analysis shows that the geochemical characteristics of the Qiaoqi intrusion bear resemblance to those of the Emeishan basalts, which are attributed to volumetrically minor melting of the fossil Emeishan plume head beneath the Yangtze crust following the eruption of the Emeishan Large Igneous Province (ELIP). This understanding further constrains the duration of the Emeishan Large Igneous Province and provides new support for understanding the formation, evolution and distribution of the Emeishan Large Igneous Province.