The origin of volatiles in the Emeishan large igneous province, China: Constraints from chemical and C–He–Ar isotopic compositions of volatiles in picrites and basalts. (19th March 2021)

• Record Type: Journal Article
• Authors: Tang, Qingyan; Bao, Jian; Su, Tianbao; Xu, Shihai; Zhang, Jiahe; Song, Hong
• Is Part Of: Geological journal. Volume 56:Number 7(2021)
• Page Start: 3626
• Page End: 3643
• Publication Date: 2021-03-19
• Subjects: Emeishan large igneous province -- He–Ar isotopes -- picrite -- sulphide‐bearing ore deposit -- volatiles; Geology -- Periodicals; 551
• DOI: 10.1002/gj.4122
• Languages: English
• ISSNs: 0072-1050

Abstract

Abstract : The Emeishan large igneous province (LIP) consists of Permian flood basalts and coeval intrusive rocks with compositions varying from mafic–ultramafic rocks to syenites and granites. The volatiles in the Emeishan LIP are dominated by H2 O with high H2, indicating that the plume‐derived magma was generated under a reduced condition. Picrite has minor contents of H2 S without detectable SO2, and the basalt samples show no detectable H2 S and SO2, indicating that the basaltic magma may have undergone sulphur‐saturation during magma evolution. The δ 13 C values of CO2 and CH4 in picrites and basalts are between the values of mantle and crustal organic carbon. This, together with the distribution patterns among CH4 homologue, indicates contribution of recycled sediments to the Emeishan mantle‐derived magma. The 3 He/ 4 He ratios of volatiles extracted from olivine and pyroxene phenocrysts of picrites vary from 0.01 to 0.66 Ra, and those from pyroxene separates of olivine websterite samples in the Zhubu intrusion vary from 0.92 to 1.05 Ra. The low 3 He/ 4 He ratios of the picrites from Emeishan LIP are lower than those from the Siberian LIP, but within the values of continental crust and oceanic crust. The positive correlation between 4 He/ 40 Arc and 4 He contents in Emeishan picrite suggests that the isotopic ratios were dramatically affected by crustal contamination rather than degassing. The He and Ar isotopes indicate that Emeishan picrite experienced addition of subducted oceanic crustal materials, and the Zhubu magma was contaminated by continental crustal materials. Abstract : The volatiles in the Emeishan LIP are dominated by H2 O with high H2 . Carbon isotope indicates the addition of crustal materials to the parental magma. He–Ar isotopes suggest Emeishan picrite underwent addition of subducted materials.