| Popis: |
The Philippine Archipelago is a complex island arc system, where many regions still lack geopotential studies. This study aims to present a general discussion of the Philippine gravity anomaly distribution. The high-resolution isostatic anomaly digital grid from the World Gravity Map (WGM) was processed and correlated with the Philippines’ established geology and tectonics. This study also investigated the gravity signatures that correspond to the regional features, e.g., geology, structures, sedimentary basins, and basement rocks of the study area. Upward continuation, high-pass, and gradient filters (i.e., first vertical derivative, horizontal gradient) were applied using the Geosoft Oasis Montaj software. The interpreted gravity maps’ results highlighted the known geologic features (e.g., trench manifestation, ophiolite distribution, basin thickness). They revealed new gravity anomalies with tectonic significance (e.g., basement characterization). The isostatic gravity anomaly map delineates the negative zones. These zones represent the thick sedimentary accumulations along the trenches surrounding the Philippine Mobile Belt (PMB). The Philippine island arc system is characterized by different gravity anomaly signatures, which signify the density contrast of subsurface geology. The negative anomalies (< 0 mGal) represent the thick sedimentary basins, and the moderate signatures (0 to 80 mGal) correspond to the metamorphic belts. The distinct very high gravity anomalies (> 80 mGal) typify the ophiolitic basement rocks. The gravity data’s upward continuation revealed contrasting deep gravity signatures; the central Philippines of continental affinity (20 – 35 mGal) was distinguished from the remaining regions of oceanic affinity (45 – 200 mGal). Local geologic features (e.g., limestone, ophiolitic rocks) and structures (e.g., North Bohol Fault, East Bohol Fault) were also delineated downward continuation and gravity gradient maps of Bohol Island. The WGM dataset’s effectiveness for geologic investigation was achieved by comparing the established geologic features and interpreted gravity anomalies. The processed gravity digital grids provided an efficient and innovative way of investigating the Philippines’ regional geology and tectonics. |
