The Macolod Corridor (Philippines)–A passive rift compensated by ponded magmas?

Abstract

The Macolod Corridor is a zone of active volcanism situated at the junction of different tectonic elements (i.e., arc-continent collision, arc volcanism, bounded by two major faults). Contentions regarding its formation arise due to its tectonic characteristic and the lack of subsurface data in the region. Its shallow and deep crustal configuration is investigated by processing novel ground gravity data and existing gravity datasets. Regional-residual separation and forward and inverse modeling of the gravity data indicate the existence of high-density bodies. These might reveal the shallow and deep magmatic bodies in the area. The shallow subsurface features reflect the trends of the reported fractures in the area, implying structurally controlled volcanic complexes. Three forward gravity models are created to evaluate the crustal structure of the region: 1) thinned arc crust, 2) normal arc crust, and 3) normal arc crust with an anomalous zone of high-density material. The forward response of the third model has the lowest error. The anomalous zone identified from the model is characterized by high-density (low-velocity and high temperature) material, possibly due to a shallower mantle material or ponded partially molten magmatic materials. The geophysical signature of the shallow crust exhibits extension-related features, as shown by the trends of the shallow high-density bodies. However, the deep crust does not indicate crustal thinning typical of extensional settings; instead, the model shows a relatively thick crust (∼34 km). This phenomenon is reconciled by the compensation of ponded magmatic materials, which act as the source of volcanism and elevated heat flux in the Macolod Corridor. This ponded material is attributed to subduction-related magmatism. The eventual crustal extension led to the formation of the arc-perpendicular volcanism in the Macolod Corridor by tapping the ponded materials in the lower crust.