Lateral variation in dike density within the lithosphere beneath the Ontong Java Plateau

The Ontong Java Plateau (OJP) is thought to have formed through large-scale Cretaceous volcanism, however the process of the massive volcanism remains largely unknown. Shito et al. [2025] explored the ascent process of the thermochemical plume and its impact on the physicochemical properties of the preexisting lithosphere. Based on the 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.

This study employed two-dimensional tomography analysis to estimate lateral variations in dike density. The model parameter is relative energy reduction of So wave to Po wave and the data is Po and So wave envelope. As the first step, the two-dimensional tomography was performed under the assumption that the observed Po/So energy ratio is a simple integral value along the great circle path. The results revealed the presence of an area in the central part of the OJP where the reduction in So wave energy is significantly greater compared to Po waves. This suggests it corresponds to an area with high dike density and, also suggests the possibility that this location is the center of a massive eruption.

Future research aims to examine quantitative relationship between dike density and energy reduction of Po and So wave and the validity of the linearity, and to estimate the two-dimensional distribution of dike density using more appropriate methods.