Interrelation of the stagnant slab, Ontong Java Plateau, and intraplate volcanism as inferred from seismic tomography

Masayuki Obayashi,Hiroko Sugioka,Hajime Shiobara,Takashi Tonegawa,Daisuke Suetsugu,Yasushi Ishihara,Satoru Tanaka,Takehi Isse,Aki Ito,Junko Yoshimitsu

doi:10.1038/s41598-021-99833-5

Abstract

We investigated the seismological structure beneath the equatorial Melanesian region, where is tectonically unique because an immense oceanic plateau, a volcanic chain and subduction zones meet. We conducted a multi-frequency P-wave tomography using data collected from an approximately 2-year-long seismic experiment around the Ontong Java Plateau (OJP). High-velocity anomalies were revealed beneath the center of the OJP at a depth of ~ 150 km, the middle-eastern edge of the OJP at depths of 200–300 km, and in the mantle transition zone beneath and around the OJP; low-velocity anomalies were observed along the Caroline volcanic island chain above 450 km depth. These anomalies are considered to be associated with the thick lithosphere of the OJP, remnant dipping Pacific slab, stagnant Pacific slab, and a sheet-like upwelling. The broad stagnant slab was formed due to rapid trench retreat from 48 to 25 Ma until when the OJP with thick lithosphere collided with a subduction boundary of the Pacific and Australian plates. This collision triggered slab breakoff beneath the arc where the dipping slab remained. The stagnant Pacific slab in the mantle transition zone restricted the plume upwelling from the lower mantle causing sheet-like deformed upwelling in the upper mantle.

Highlights

We investigated the seismological structure beneath the equatorial Melanesian region, where is tectonically unique because an immense oceanic plateau, a volcanic chain and subduction zones meet
The equatorial Melanesian region is characterized by intense tectonic activities: subduction zones along Papua New Guinea, Solomon Islands, and Vanuatu islands to the south, the Ontong Java Plateau (OJP) near the equator, and Caroline volcanic chain to the north
The northeastern part of flat slabs beneath the OJP may be intuitively interpreted as stagnant Australian slabs, because they lie in the advancing direction of the Australian plate that currently subducts beneath the Pacific plate

Summary

Introduction

We investigated the seismological structure beneath the equatorial Melanesian region, where is tectonically unique because an immense oceanic plateau, a volcanic chain and subduction zones meet. High-velocity anomalies were revealed beneath the center of the OJP at a depth of ~ 150 km, the middle-eastern edge of the OJP at depths of 200–300 km, and in the mantle transition zone beneath and around the OJP; lowvelocity anomalies were observed along the Caroline volcanic island chain above 450 km depth These anomalies are considered to be associated with the thick lithosphere of the OJP, remnant dipping Pacific slab, stagnant Pacific slab, and a sheet-like upwelling. Through the results of this study, we illustrate the extended high-velocity anomalies in the mantle transition zone beneath the OJP and the sheet-like low velocity anomalies along the Caroline Islands, and discuss their relation and impacts on the surface tectonics

Results

Discussion

Conclusion