Maturity evolution of Permian source rocks in the Sichuan Basin, southwestern China: The role of the Emeishan mantle plume

Abstract

The Permian source rocks in the Sichuan Basin, Southwestern China, are hypothesized to have undergone thermal over-maturation associated with the Emeishan mantle plume. In this study, by comparing the maturity evolution of Permian source rocks, we identified three maturity evolutionary patterns, including (1) Middle Permian maturing abrupt jump in the areas where the Permian magmatic intrusions, (2) Mesozoic continuous heating in the southwestern Sichuan Basin, and (3) Middle-Late Triassic heating cessation common in the Sichuan Basin. Furthermore, we assess the evolution model of the Emeishan large igneous province and investigate the thermal effect of the mantle plume on hydrocarbon maturation of Permian source rocks. During the mid-Guadalupian, the mantle upflow reached the base of the northeastern Sichuan Basin and little eruptions and intrusions formed along the basement faults. As the South China block kept moving northward, the major eruption and crustal magma underplating occurred at the end-Guadalupian near the southwest margin of the Sichuan Basin. The mantle plume caused the Middle-Lower Permian source rocks in the intrusion area to mature rapidly and achieve peak maturity (Requ > 3%) during the Middle Permian. Except for the areas with magma intrusion, the mantle plume had no obvious impact on the maturity evolution of the Permian source rocks and the maturity evolution is controlled by Mesozoic sedimentation and uplift. In addition to providing new insights into the thermal effects of the Emeishan Permian mantle plume, this study has great implications for gas exploration in the Sichuan Basin.