Multichannel seismic constraints reveal basement structures and generation mechanism of oceanic crust in the West Philippine Basin

The mechanisms of oceanic crustal generation in back-arc settings remain poorly constrained. Here， we present a 1400-km seismic transect that crosses the Central Basin Fault rift， providing a new view of sedimentary cover and intrabasement reflections across three oceanic crustal domains (A-C) formed during the early Oligocene. Our results reveal pronounced spatial heterogeneity. In oceanic crustal domain A， the basement exhibits three groups of seismic facies， including chaotic facies that are characterized by high-amplitude and discontinuous reflectors， layered facies that are laterally continuous， and imbricate facies with inclinations decreasing away from basement highs. These features are interpreted as evidence of multiple magma sources and lateral magma flow， likely linked to mantle plume activity associated with the Benham hotspot at ～40-35 Ma. In oceanic crustal domain B， the basement high with chaotic reflections is locally developed， and laterally discontinuous layered reflections occur near the basement high， suggesting extension with local magmatic intrusion. In oceanic crustal domain C， the basement is structurally tilted with truncated strata， and slump bodies are developed above a prominent decollement surface， which is indicative of extensional and strike-slip faulting. Collectively， our findings demonstrate that plume-related magmatism， normal faulting with local magmatic intrusion， and extensional and strike-slip faulting controlled the generation of oceanic crust in different sectors of the West Philippine Basin. This study reveals that multiple tectonic processes can result in the production of spatially heterogeneous oceanic crust in back-arc basins.