Subduction of the Ontong Java Plateau: Insights from seismic reflection imaging of the forearc along the West Melanesian Trench

The Ontong Java Plateau (OJP), as the largest oceanic plateau in the world, has drawn much attention because of its subduction along the West Melanesian Trench and the North Solomon Trench. Based on the first observed multichannel seismic (MCS) and multibeam data across the northwestern margin of the OJP, we show that the forearc region along the West Melanesian Trench is dominated by a series of normal faults which show this trench as an erosive subduction zone. Under the control of the seaward-tilting normal faults, the forearc region presents the topographic characteristics of gradually descending toward the trench and can be divided into the upper slope, middle slope and lower slope. However, some areas of the forearc region may be affected by underplating duplex deformation at the upper/lower plate interface, which leads to the formation of the outer-arc high and modification of the early tectono–stratigraphic structure, along with a series of arcward-tilting normal faults. We suggest that the forearc region between New Ireland Island and the West Melanesian Trench generally exhibits a strong extension, which is in sharp contrast to the thrust-imbricate collage of the forearc region east of the Solomon Islands. The extension indicates that the buoyant OJP is not subducted beneath the New Ireland Island along the West Melanesian Trench but may be collocated only with the overriding island arc system, as evidenced by no relative motion between the Pacific Plate and the New Ireland Island Arc and few earthquakes in the inactive trench.