Terrane Boundary Geophysical Signatures in Northwest Panay, Philippines: Results from Gravity, Seismic Refraction and Electrical Resistivity Investigations

Abstract

Northwest Panay consists of two terranes that form part of the Central Philippine collision zone: Buruanga Peninsula and Antique Range. The Buruanga Peninsula consists of a Jurassic chert-clastic-limestone sequence, typical of oceanic plate stratigraphy of the Palawan Micro-continental Block. The Antique Range is characterized by Antique Ophiolite Complex peridotites and Miocene volcanic and clastic rocks, representing obducted oceanic crust that serves as the oceanic leading edge of the collision with the Philippine Mobile Belt. The Nabas Fault is identified as the boundary between the two terranes. This study employed the gravity method to characterize the Northwest Panay subsurface structure. Results indicate higher Bouguer anomaly values for Buruanga Peninsula than those for Antique Range, separated by a sudden decrease in gravity values toward the east-southeast (ESE) direction. Forward gravity data modeling indicates the presence of an underlying basaltic subducted slab in the Buruanga Peninsula. Furthermore, the Nabas Fault is characterized as an east-dipping thrust structure formed by Buruanga Peninsula basement leading edge subduction beneath Antique Range. Additional geophysical constraints were provided by shallow seismic refraction and electrical resistivity surveys. Results from both methods delineated the shallow subsurface signature of the Nabas Fault buried beneath alluvium deposits. The gravity, seismic refraction and electrical resistivity methods were consistent in identifying the Nabas Fault as the terrane boundary between the Buruanga Peninsula and the Antique Range. The three geophysical methods helped constrain the subsurface configuration in Northwest Panay.

Imaging crustal features and Moho depths through enhancements and inversion of gravity data from the Philippine island arc system

“…Gravity surveys have undergone continuous development during the past twenty years. Ground and marine gravity surveys were employed by several studies focusing on specific regions-e.g., the crustal structure and tectonic evolution along Manila Trench (Hayes and Lewis 1984), the emplacement of Bohol ophiolite (Barretto et al 2000); the regional tectonics of northern Luzon (Milsom et al 2006), the arc-continent collision in the central Philippines (Dimalanta et al 2009), the crustal thickness of Central Philippines (Manalo et al 2015), the upper crustal structure beneath Zambales Ophiolite Complex (Salapare et al 2015), and the terrane boundary in northwest Panay (Gabo et al 2015).…”