Construction of the Caroline Ridge Uppermost Basement in the West Pacific: Implications from Intrabasement Seismic Reflectors

The construction model of the Caroline Ridge uppermost basement is still unresolved, requiring more inference from limited geophysical observational data. Here, we systematically reveal intrabasement seismic reflectors of volcanic sequences within the rifted and subsidence domains of the Caroline Ridge. Extrusive centres and three types of intrabasement reflectors, that is, relatively horizontal, ridgeward-dipping and folded reflectors, have been identified. Extrusive centres in the rifted domain are characterized by domal shapes and produce sub-parallel stratified intrabasement reflectors within the conduits that connect with the relatively horizontal reflectors distributed on both sides of the basement highs. Intrabasement reflectors display increasing dip angles away from the extrusive centre and present ridgeward-dipping reflectors but not troughward-dipping reflectors in subsidence domain 1, suggesting a brittle deformation process. Layered intrabasement reflectors are developed within subsidence domain 2 but display folded and mounded morphologies, suggesting a ductile deformation process. We propose that the Caroline Ridge formation was supported by discrete extrusive centres, and the uppermost basement construction model has experienced stages of transition from brittle deformation to ductile deformation, which can provide new clues for the early-stage crustal evolution of global oceanic plateaus.