GEOLOGICAL SOCIETY OF THE PHILIPPINES

 

EVIDENCE OF NO-COLLISION IN PRESENT-DAY NORTH PALAWAN-PANAY-MINDORO AREA

 

Aurelio, M.*, R. Savella, R.** and Caagusan, N.*
* Mines and Geosciences Bureau, North Avenue, Diliman, Quezon City, Philippines
** Philippines National Oil Company-Exploration Corporation
*** Petrofields Corporation

 

          Recent GPS data from a 4-year observation period of a Southeast Asian wide network reveal that present-day plate movements in the western sector of the Philippines are not coherent with active collisional processes. When Palawan, representing the stable platform is held fixed, most of the motion vectors in the Philippines can be explained by active deformation along major structures except those observed in the North Palawan-Mindoro-Panay area. The relative motion between Panay Island and Palawan is characterized by an essentially northward (Azimuth: 365) vector moving at a rate of about 21 mm/yr. The strain within this triangle is virtually extensional directed NW-SE. This implies that Panay Island is not presently "colliding" with Palawan, contrary to the accepted theory of a Palawan-Mindoro-Panay collision zone. Instead, what is suggested is the northward movement of Panay with respect to Palawan along a north trending boundary. The only known structure in the vicinity is the Negros Trench. Such a movement would not allow frontal subduction along the trench, but instead favor left-lateral strike–slip movements along possible relay zones in the subduction-collision transition zone. Few earthquake focal mechanism solutions on the northern segment of the Negros Trench show left-lateral faulting along north-trending structures, but known strike-slip fault in the region are right-lateral such as the Tablas Lineament and the Mindoro Fault. Initial review of offshore data in the Panay-Mindoro-Palawan area suggests the presence of active strikes-slip and possibly, thrust fold zones further north.

 
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