Development of Yap Islands and Tectonics of the Philippine Sea Plate at Its Southern Tip

Abstract

Yap Islands fringing southeastern margin of the Philippine Sea plate consist chiefly of metamorphic rocks which are not expected to exist on common oceanic islands. A model for the formation of such anomalous island arc is present by showing spontaneous down going slab at the paleo-Kyushu-Palau transform fault after change of the direction of the movement of the Pacific plate from NNW to WNW at 42Ma.
Amphibolites, amphibolite-cataclasites and debris flow deposits consisting mostly of amphibolite were formed during the process of the ocean floor metamorphism of the West Philippine Basin followed by the activity of the fault movements of the transform fault and finally uplifting of the paleo Yap terrain.
Island arc type volcanism took place after the deposition of channel fill sediments in the forearc area and ceased at about 10Ma by the collision of the Caroline Ridge with Yap Arc system.