Complexity of the Oligocene meridional motion of the Philippine Sea Plate

Abstract The kinematic reconstruction of the Philippine Sea Plate (PSP) holds significant importance in elucidating the Australia–SE Asia collision and the Pacific Plate subduction. Previous studies suggested an overall northward motion of the PSP since its inception, but this first-order kinematic model cannot account for the observed inconsistencies in the northward drift distances among certain sites. Here, we conducted high-resolution Oligocene magnetostratigraphic and paleomagnetic research from Deep Sea Drilling Project (DSDP) Site 445, showing that the paleolatitudes of Site 445 were 11.9° ± 1.9° (29.2 Ma), 9.1° ± 3.7° (27.4 Ma), 8.8° ± 2.6° (25.6 Ma), 13.5° ± 2.8° (24.6 Ma), and 15.0° ± 2.5° (23.3 Ma). These results indicate that the PSP exhibited a detectable southward-moving trend during the 29–25 Ma period, followed by a northward motion after 25 Ma. The new finding challenges the previously held belief that the PSP consistently migrated northward. This phenomenon can be attributed to the rollback of the subducted slab south of the PSP prior to 25 Ma and a subsequent collision between the Australian Plate and the PSP after that. The tectonic reorganization around 25 Ma can also be identified in the Pacific Plate and the convergence between the Indian and Asian Plates. Therefore, this event bears great significance in deepening our understanding of the global plate evolution.