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,Geological Journal

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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
Geological Journal ( IF 1.8 ) Pub Date : 2021-03-19 , DOI: 10.1002/gj.4122
Qingyan Tang ₁ , Jian Bao ₁ , Tianbao Su ₁ , Shihai Xu ₁ , Jiahe Zhang ₁ , Hong Song ₁

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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 H₂O with high H₂, indicating that the plume-derived magma was generated under a reduced condition. Picrite has minor contents of H₂S without detectable SO₂, and the basalt samples show no detectable H₂S and SO₂, indicating that the basaltic magma may have undergone sulphur-saturation during magma evolution. The δ¹³C 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 ³He/⁴He 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 ³He/⁴He 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 ⁴He/⁴⁰Arc and ⁴He 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.

更新日期：2021-03-19

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