Origin of microplates under oblique subduction system in New Guinea: Inferences from gravity and magnetic data

Abstract

The New Guinea Island is formed under the oblique subduction of the Pacific Plate. The formation and evolution of the microplates around the New Guinea Island are complex and still poorly understood. Here we use the published gravity, magnetic datasets and the CRUST1.0 model, combined with the wavelet multi-scale decomposition and residual crustal gravity anomaly separation, to analyze the crustal structure and boundary characteristics of different microplates. The results show that the gravity and magnetic anomalies have good responses to microplate boundaries, such as deep-seated large-scale faults and subduction zones. Seven microplates (including the Caroline, the North Bismarck, the Manus, the South Bismarck, the Solomon Sea, the Woodlark and the Ontong Java Plateau microplates) have been identified based on their different geophysical properties. Combined with other geological records and plate reconstruction, we analyze the regional tectonic activity, dynamics and microplate evolution in this region. The New Guinea Island was formed and shaped by the oblique subduction of the South Pacific since the Late Cretaceous. Several key events are recorded at 45 Ma, 25 Ma and 5 Ma, which are highly related to the formation of the microplates in the convergent margin. The key events mainly involve the formation and termination of the Melanesian Arc, the collision between the Ontong Java Plateau and the Solomon Islands, and the arc-continent collision at the New Britain Island Arc. These events contributed to a series of island arcs and back-arc basins that further evolved into relatively independent microplates. By analyzing the formation patterns and boundaries of microplates, we classify these microplates into the accretion-derived, collision-derived and back-arc rifting-derived types. The evolution history of each type of microplate is reconstructed in details, which provides additional constraints on the Cenozoic tectonic reconstruction of the Southwest Pacific region.