Peridotites and volcanics from the Yap arc system: implications for tectonics of the southern Philippine Sea Plate

Satellite altimetry reveals a continuous, N20°E-trending bathymetric feature, extending from the Yap Trench through the North Yap Escarpment (NYE) to the Parece Vela Rift, suggesting a genetic relationship. We report the results of submersible observations and geochemical study of peridotites and volcanics from the Yap Trench and the North Yap Escarpment, and use these to understand the genesis and evolution of the Yap arc system. Metamorphosed rocks and gabbros of the Parece Vela Basin origin predominate on the Yap Islands and for the upper part of the forearc, although minor remnant arc volcanics of ∼25 Ma age exist. There are also arc volcanics of 11–7 Ma age in the forearc, whereas depleted arc-type mantle peridotites are exposed along faults in the lower part of the forearc landward slope. The results show that the Yap arc–North Yap Escarpment system might form as an incipient arc system at the propagating tip of the Parece Vela Rift at ∼25 Ma, and that the overall Yap arc–forearc region is composed of several different units.