Along-strike variations in oceanic crustal deformation along the Central Basin Fault, West Philippine Basin

Abstract

Rifting of pre-existing oceanic lithosphere in subduction systems plays a crucial role in understanding oceanic crust formation, yet it remains inadequately studied. The Central Basin Fault (CBF) in the West Philippine Basin (WPB), a hyper-extensional center that developed subsequent to the primary seafloor spreading phase, offers an exceptional setting for investigating oceanic rifting processes. Utilizing published gravity and seismic data and an integrated approach combining 3D Moho inversion and 2D crustal structure modeling, we elucidate significant along-strike variations within the CBF. Our analysis reveals a striking transition in fault pattern and magmatic activity: from symmetric, magma-rich extension in the western segment, through a central segment of minimal deformation, to asymmetric, magma-poor extension in the eastern segment. Notably, the eastern termination exhibits ultra-thinned crust and potential serpentinized mantle exhumation, indicative of localized intense deformation during the final stages of extension. Integrating our results with previous volcanic ages, we propose that the CBF originated from intensive deformation associated with Kyushu-Palau Ridge (KPR) rifting. This comprehensive study reveals a scenario of intensive deformation preceding the cessation of seafloor spreading, where pre-existing lithospheric fabric, regional tectonic forces, and localized magmatism strongly influence deformation patterns. Our findings provide novel insights into oceanic crustal evolution beyond the primary spreading stage, elucidating the complex processes shaping oceanic lithosphere within a subduction system context.