CENTRAL EMEISHAN FLOOD VOLCANISM: SUBAQUEOUS VOLCANO GROWTH WITH NO PRE-ERUPTIVE UPLIFT INDUCED BY MANTLE PLUME

Emeishan Large Igneous Province (ELIP) located in Southwest China became one of the most famous cases in current LIP studies, not only for its temporal link between its generation (~260 Ma) and the Middle Permian extinction, but also for that the ELIP is regarded as a best example of crustal doming. The model had been challenged by growing understanding of ELIP. The issue is hotly debated with no consensus, because the eruption environment of the central ELIP, which is significant to constrain whether the uplift existed, remains poorly understood.

We studied the central ELIP and subdivided its sequences into three sub-successions. The lowermost Basal Succession (>200 m) consists of thick pillow lavas piles associated with hyaloclastites. The above Lower Succession (>2000 m,) are mafic volcaniclastic deposits (MVDs) intercalated with subaqueous lavas. Pillow breccias, palagonites and non-welding features give an implication of subaqueous explosive eruption and pyroclastic density current transitions. Upper Succession (2600 m) mainly consists of subaerial flood lava flows and fallout tuffs.

Pillow basalts and hyaloclastites are evidences of subaqueous eruptions. The absence of explosive MVDs in Basal Succession implied that the initial eruption occurred in a deep marine environment probably generated by subsidence or rifting. The overlying Lower Succession represents early eruptions. Abundant explosive materials reflect the early-stage volcanism erupted at shallow level where explosive hydromagmatism became possible. Upper Succession indicates that the volcanic edifice has emerged out of the sea level.

Frequent subaqueous volcanism from the Basal and Lower Successions are impossible to be produced in an uplifted erosional terrestrial background. The ‘uplift’ recorded in the strata is rather to be interpreted as a growth history of the central volcanic edifice drove by continuous emplacement of volcanic materials. The growth began with an initial deep marine stage, following by an early shoaling stage and final entered into a terrestrial flooding stage when it totally emerged out of the sea level.