Subduction dynamics of the New-Guinea-Solomon arc system: Constraints from the subduction initiation of the plate

A complicated subduction system, the New-Guinea-Solomon arc (PN-SL), exists in the convergent boundary between the Indo-Australian and Pacific plates at the eastern end of the Neo-Tethyan tectonic domain. Since late Cretaceous, the PN-SL system has gradually become a complex trench-arc-basin-oceanic plateau system suffered various stages of subduction. Constrained by the multi-stages and multi-types of plate subduction initiation, the deep structure of the PN-SL subduction system varies dramatically in space. Among the subduction zones within the PN-SL subduction system, the extension depth of the subducting plate changes from over 500 km to nearly 100 km and the dip angle of the plate decreases from over 70° to 30°. The Ontong Java Plateau, the largest oceanic plateau in the world, is located in the east of the PN-SL subduction system. Owing to the large crustal bulge and associated low-density structure, the tectonic framework of the PN-SL subduction system is reconstructed. Driven by the subduction of the Ontong Java Plateau, the Solomon Sea back-arc basin has subducted beneath the Pacific ocean towards northwest, northeast and southwest directions since Miocene, sharply contrasted with the classical binary model of the subduction polarity reversal and transference or trench jump induced by the subduction of the buoyant lithosphere. This indicates that the convergent deformation process between the Ontong Java Plateau and the PN-SL subduction system cannot just be interpreted as the change in plate density. Complex tectonic environment and various tectonic elements must be considered in the studies on the subduction and convergent deformation of the oceanic plateau. In particular, as an important influence factor of the strength of the lithosphere, the fluid activity of the subduction system, which may induce the strength weakening and decrease in the melting point of the lithosphere, must be carefully considered. Moreover, the fluid may be transported into the deep part of the Earth together with the subduction of plate and make contributions to the dehydration of plate and the hydro-metasomatism within the mantle wedge, which changes the composition and rheological properties of the crust and mantle and induces partial melting of the mantle wedge and island magmatism. Therefore, it is concluded that fluid plays an important role in the subduction initiation and evolution as a key entry point for understanding the subduction tectonic dynamics of the plate.