Structural and Gravity-based Analysis of Crustal Thickness Variations in Central Philippines

Abstract

The tectonic setting of Central Philippines reflects its complex history of arc-continent collision, subduction-related compression along the Manila Trench, and strike-slip deformation associated with the Philippine Fault System. Key segments, such as the Verde Island Passage Fault and the Sibuyan Sea Fault, traverse internal seas within the region and contribute to numerous structural expressions. In this study, mantle residual gravity anomalies derived from WGM2012 were analyzed using Euler deconvolution to investigate regional variations in crustal thickness. Results indicate an average crustal thickness difference of approximately 5 km between the Palawan Microcontinental Block and the Philippine Mobile Belt. Within these two tectonostratigraphic terranes, transpressional and transtensional regimes also result in localized thickening or thinning, respectively. Crustal thickness can reach upwards of 33 km along ophiolite belts and a minimum of 27 km beneath offshore basins. The thickened crust beneath ophiolites in Mindoro, Romblon, and Panay reflects accretion during arc-continent collision, whereas thinning beneath the intervening seas is consistent with pull-apart basin development driven by differential block motion. In a broader sense, this study demonstrates that inversion of gravity data is a viable alternative for constraining crustal thickness in areas with limited seismic coverage.