Seismic and Gravity Data Analysis of Oceanic Core Complexes in the West Philippine Basin: Insights into Along-Strike Variations and Formation Processes

Abstract

This study explores the formation of Oceanic Core Complexes (OCCs), hypothesized to arise from long offset, active normal faults that exhume the lower crust and upper mantle to the ocean floor. OCCs are predominantly observed in asymmetric crustal accretion zones, especially where magma supply is limited, such as in slow-spreading mid-ocean ridges. Traditional observational approaches, mostly perpendicular to these ridges, have suggested that spreading rates are a critical factor in OCC genesis. However, a lack of comprehensive data along the strike of mid-ocean ridges has limited our understanding of the interaction between tectonic and magmatic processes in OCC formation. Our investigation commenced with the utilization of recently acquired seismic data from the spreading center of the West Philippine Basin. This exceptional dataset has allowed us to chronologically trace the development of multiple distinct OCC structures along the mid-ocean ridge. Complemented by satellite gravity data, we further verified the interpretation of the OCC. The results indicate significant density variability within OCCs, ranging from 2.55 to 3.3 g/cm^3, in contrast to the narrower range of 2.74 to 3.1 g/cm^3 observed in normal oceanic crust. The integration of seismic interpretation and gravity data inversion exposes an alternating sequence of magma-poor and magma-rich segments along the ridge axis. This sequence demonstrates a shift in magmatic activity, transitioning from Penrose-type to Chapman-type crust, characterized by the sequential development of detachment faults and OCCs, ultimately reverting to Penrose-type in the eastern segment. Consequently, our findings propose that, in addition to spreading rates, the localization and delocalization of strain along structural strikes play a pivotal role in OCC evolution. This perspective provides a nuanced understanding of the dynamic interactions between tectonic and magmatic processes that shape the oceanic crust.