Dike Swarms in the Oceanic Lithosphere Beneath the Ontong Java Plateau

The Ontong Java Plateau (OJP) is believed to have formed through large‐scale Cretaceous volcanism, but the impact of the massive volcanism on the lithosphere remains largely unknown. In this study, the ascent process of the thermochemical plume and its impact on the physicochemical properties of the pre‐existing lithosphere were explored. High‐frequency seismic wave analysis revealed that the internal structure of the lithosphere beneath the OJP is a hybrid structure comprising dike swarms that are superimposed on the laminar structure. Moreover, the lithosphere exhibits lower seismic wave velocities than normal oceanic lithosphere, suggesting that the lithospheric mantle was physicochemically altered by the intrusion of dike swarms filled with magma from a large‐scale thermochemical plume. Our results advance the current understanding of the alterations in the lithosphere caused by a thermochemical plume.