THE ONSET OF MOVEMENT ON THE PHILIPPINE FAULT IN EASTERN MINDANAO - ATRANSITION FROM A COLLISION TO A STRIKE-SLIP ENVIRONMENT

The spatial and temporal evolution of eastern Mindanao from a zone of active are-are collision to one of pure strike slip environment is add ressed. This is made possible by tracing the Philippine Fault, confine d to a well defined and narrow zone of deformation, and by differentia ting from it earlier collision-related compressional features, whose d eformation is distributed over a broad zone. A diachronous unconformit y marking the end of collision-related deformation reflects the southw ard propagating nature of the collision and provides limits on the age of initiation of the Philippine Fault. This diachronism suggests that the initiation of the Philippine Fault is related to the completion o f the collision. We show the rapidity at which formation and propagati on of the fault follows the locking of the collision zone. We likewise demonstrate that the Philippine Fault reactivates pre-existing collis ional features in cutting across the southern Pacific Cordillera.