GEOLOGICAL SOCIETY OF THE PHILIPPINES
The Role of the Benham Rise in the Geodynamic Evolution of the Philippines
Advances in the understanding of how oceanic plateaus disturb subduction from worldwide examples, warrants a reinterpretation of Philippine tectonics with respect to its collision with the Benham Rise, an oceanic plateau east of Luzon. Analysis of available seismic, gravity, bathymetric, structural, paleomagnetic and petrologic data to date, suggests that the Benham Rise collided with eastern Luzon during the early Miocene and had a profound impact on the tectonics of the Philippine archipelago as well as the Philippine Sea Plate. Prior to the collision of the Benham Rise, the Philippine trench was a relatively long and linear feature. The collision caused bending of the trench and segmentation of the once linear feature into two units, the East Luzon Trough and the Philippine Trench. Soon afterwards, subduction along the proto East Luzon Trough reduced considerably due to the docking of the Benham Rise at the trench. As a result, flipping of the subduction zone from west to east took place and the Manila trench was formed. The collision also promoted clockwise rotation of the Philippine Sea Plate as continued subduction took place further north. Movement along the Philippine Trench was reinitiated during the Pliocene when the Palawan-Mindoro continental block collided with the Philippines. The temporal break in subduction along the Philippine Trench from Early Miocene to Pliocene is manifested as a detached slab seen in Benioff Zone profiles from 5° to 10° latitude. Upon reactivation of the Philippine Trench, the Philippine Sea Plate may have began rotating in counter-clockwise motion. The interpretation in this paper presents a straightforward application to the Philippines of the known effects of oceanic plateau collisions. Major points on the geodynamics of the Philippines are addressed and their interpretation simplified.
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