The internal structure of submarine arc volcanoes remains poorly resolved, limiting our understanding of the interactions among magmatism, tectonics, and hydrothermal circulation. We investigated the Tofua Arc 12 (TA12) seamount in the Lau Basin using multibeam bathymetry and shipborne magnetic data processed through International Geomagnetic Reference Field (IGRF) correction, reduction to the pole (RTP), analytic signal analysis, and three-dimensional magnetization vector inversion (MVI). Magnetic anomaly maps show elevated amplitudes along the caldera rim and lower amplitudes within the depression. The full-vector MVI approach further resolves depth-dependent variations in both magnetization amplitude and direction, with enhanced values from ~ 3 km below sea level (bsl) upward concentrated along the caldera rim and beneath the depression, consistent with possible sill-like intrusions and subsequent cone-building episodes. In contrast, relatively low magnetization in parts of the depression and slump sectors is consistent with hydrothermal alteration and/or disaggregated materials. Independent comparison with published seismic profiles provides qualitative constraints on rim-bounding faults, mass-wasting surfaces, and a shallow basement interface near ~ 2 km bsl. We propose a conservative three-stage evolutionary model involving an initial caldera-forming eruption, later intrusions and cone growth, and fault-controlled fluid circulation, while explicitly acknowledging the resolution limits imposed by shipborne survey line spacing. These results demonstrate that integrating full three-dimensional MVI with complementary geophysical constraints can provide a reproducible framework for imaging submarine arc volcanoes and guiding future near-bottom surveys and resource assessments in back-arc basins.
Choi et al. (Fri,) studied this question.