Emeishan mantle plume activity and carbon isotope responses in the Middle Permian, South China

Abstract

During the Permian, Emeishan mantle plume activity created a large igneous province and deeply impacted carbon isotope records in marine carbonate strata in South China. To evaluate the isotopic variations caused by this catastrophic event, 140 carbonate samples from four sections were collected and analyzed. The δ13Ccarb values in the upper section of the Qixia Formation gradually increased, stabilized at ~4.0‰ in the lower-middle sections of the Maokou Formation, and then abruptly decreased in the upper section of the Maokou Formation. This isotopic evolution trend is likely related to mantle plume geochemical processes occurring during these respective stages. Large amounts of upwelling heat from the emplacement of the mantle plume triggered large-scale decarbonation reactions in the continental crust resulting in CO2 production enriched in 13C. Substantial amounts of 13C-enriched CO2 directly affected the isotope compositions of marine carbonates during this time. Temporal and spatial fluctuations in carbon isotopes were also controlled by terrestrial materials as a result of regression and doming caused by plume emplacement. The abrupt decrease in δ13Ccarb in the upper section of the Maokou Formation reflects the onset of volcanism, resulting in the breakdown of organic materials. These findings emphasize the contribution of a carbon reservoir (with a thermal decarbonation origin) in the upper crust, particularly against the Permian tectono-thermal background. This mechanism, which is similar to biological isotope fractionation in the carbon cycle, should not be overlooked.