Sedimentary evidence for a rapid, kilometer-scale crustal doming prior to the eruption of the Emeishan flood basalts

Biostratigraphic and sedimentologic investigations in 67 sections have been carried out for the Middle Permian Maokou Formation that immediately underlies the Emeishan flood basalts in southwest China. The results suggest a domal crustal thinning before the emplacement of the Emeishan large igneous province. Variably thinned carbonates in the Maokou Formation are capped by a subaerial unconformity, which is generally manifested by karst paleotopography, paleoweathering zone, or locally by relict gravels and basal conglomerates. Provenance analysis indicates that these gravels and conglomerates were mainly derived from the uppermost Maokou Formation. Therefore, the stratigraphic thinning likely resulted from differential erosion due to regional uplift. Iso-thickness contours of the Maokou Formation delineate a subcircular uplifted area, in accordance with the crustal doming caused by a starting mantle plume as predicted by experimental and numerical modeling. The duration of this uplift is estimated to be less than 3 Myr and the magnitude of uplift is greater than 1000 m. The sedimentary records therefore provide independent supporting evidence for the mantle plume initiation model for the generation of the Emeishan flood basalts.