Magnetic field characterization of Macolod Corridor (Luzon, Philippines): New perspectives on rifting in a volcanic arc setting

The Macolod Corridor (MC) is a NE-SW trending zone of Quaternary volcanism which perpendicularly bisects the Luzon Arc. This peculiar zone of volcanism is in a junction of different tectonic elements. This led to several models of formation associated with subduction or crustal extension-related processes. New information about its subsurface structure can provide constraints in resolving outstanding questions on its tectonic development. However, elucidating the origin and deep structure of the MC has been problematic due to the extensive young volcanic deposits that blanket the area. In this study, ground magnetic and aeromagnetic datasets are merged to characterize the magnetic signature in the MC. Short wavelength and high amplitude anomalies suggest complex interactions of magnetic bodies within the region. Edge detection techniques reveal linear magnetic anomalies with NE-SW, NW-SE, and E-W trends in the Corridor. These may indicate rift structures at depth. Analytic signals show maximum amplitudes over volcanic centers suggesting maximum magnetic property contrasts due to deep structural controls. Euler solutions cluster in the NE-SW, NW-SE, and E-W trends. These may correspond to conjugate structures at depth suggesting the primary role of the NW-SE shearing between the bounding Philippine Fault and the Sibuyan Verde Passage Fault. Clustering of solutions in a graben-like pattern is also observed beneath volcanic complexes indicating an extensional regime. The MC is also characterized by a shallow magnetic basement as reflected in the Curie point depths. This may be attributed to high heat flow associated with active volcanism and probably crustal thinning. These results skew our interpretation to a rift-related origin of the MC. Thus, it is interpreted to be the manifestation of the continuum of tectonic processes including near-field influences (shearing between the two bounding faults) and far-field influences (arc-continent collision and resulting northwestward translation of the Philippine Mobile Belt).