Heterogeneous morphology of the Solomon Sea slab along the New Britain Trench and its dynamic implications from the analysis of seismicity and gravity anomalies

Abstract

The New Britain-North Solomon subduction system is located at the convergence boundary between the Indo-Australian and Pacific plates. In the Cenozoic, the subduction system gradually evolved into a complex system containing the trench, arc, back-arc basin and oceanic plateau with the subduction and collision of the Ontong Java Plateau, which becomes one of the best places to explore the subduction dynamics. We attempt to illustrate the morphology of the Solomon Sea slab's response to the collision of the Ontong Java Plateau along the New Britain Trench through the hypocentral distribution, focal mechanisms and density structure from the gravity anomalies.According to the hypocenters and focal mechanisms, the focal stress field of the subducted Solomon Sea Plate along the New Britain Trench is analysed and the spatial distribution pattern of the plate is determined. We found that the maximum subduction depth of the Solomon Sea Plate gradually decreases from $600 to $400 km and the morphology of the slab changes from the steep-dipping subduction to slab roll-back from the Green and Buka Islands to the Bougainville Islands. Indicated by the analysis of seismicity and gravity anomalies, the spatial differences of the subduction pattern in the Solomon Sea Plate along the New Britain Trench are closely correlated with the block of the upper mantle in the Ontong Java oceanic Plateau, which is characterized by a tendency of thickening from NW to SE along the North Solomon Trench.