Post 8 Ma reconstruction of Papua New Guinea and Solomon Islands: microplate tectonics in a convergent plate boundary setting

Papua New Guinea and the Solomon Islands are located in a complex tectonic setting between the converging Ontong Java Plateau on the Pacific plate and the Australian continent. Here we present a Late Neogene to Quaternary plate tectonic reconstruction for this region. The reconstruction was performed using GPlates software and is based on data derived from multiple geological datasets, including seafloor magnetic isochrons, 3D models of subducted slabs, palaeomagnetic data, deformation patterns, and the spatio-temporal distribution of arc magmatism. The reconstruction shows that since ca. 6 Ma, the crustal elements that comprise Papua New Guinea and the Solomon Islands began interacting in advance of the impending collision between the Ontong Java Plateau and Australian continent, leading to the inception of regional microplate tectonics and escalation in tectonic complexity. The Bismarck Sea initially formed as a back-arc basin behind the New Britain arc, but was later modified during arc-continent collision. Following collision, the west Bismarck Sea developed into a transpressional zone associated with subduction of the Caroline plate and North Bismarck microplate at the New Guinea trench. Farther east, seafloor spreading occurred in response to the clockwise rotation of the South Bismarck microplate relative to the Australian plate. The Solomon Sea plate was subjected to anticlockwise rotation relative to Papua New Guinea, primarily due to the west-dipping subduction at the New Britain trench, which resulted in initiation of subduction at the Trobriand trough and extension in the Woodlark Basin from ca. 5 Ma. Crustal shortening in the upper plate, which now forms the Solomon Islands, resulted from the resistance of the relatively hot and buoyant Woodlark Basin lithosphere to subduction at the San Cristobal. Our reconstruction shows that tectonism at convergent plate boundaries could involve an intricate relationship between microplate rotations, seafloor spreading and subduction segmentation over timescales considerably less than 10 million years. By unraveling the tectonic evolution of this complex region, we provide insights into the development of microplate tectonics at convergent margins in general, and the possible diagnostic geological records that might be preserved in ancient orogenic systems