Origin of the Palau and Yap trench-arc systems

Abstract

This paper attempts to account for several unique morphological and geological characteristics of the Palau and Yap trench-arc systems in the northwestern Pacific Ocean using a new hydrodynamic model postulated herein. The model is a simple mathematical treatment of a stationary viscous flow pattern in the asthenosphere that causes an appreciable amount of mechanical resistance against a vertically subducted rigid slab moving horizontally together with the flat plate. A couple of thrusting forces comprising uplifting pressure generated in the frontal edge of the overriding lid and a new type of tectonic erosion along the surface of the vertical slab seem to reasonably explain apparently contradictory features of the Palau and Yap trench arcs. Long-term GPS measurements show that the Palau and Yap trench arcs are moving over the viscous asthenosphere toward the NWW with velocities as great as 10 cm yr-1. Stresses along the trench arcs predicted by the model would be sufficiently large to maintain their present morphology: (1) water depths greater than 8000 m in spite of the extremely small plate convergence rates and relatively young ages of subducted plate; (2) V-shaped cross-section of the axial bottom of these trenches, implying little cover of slumped deposits in spite of very steep landward slopes; (3) serpentinized peridotites, gabbros, basalts and limestones are exposed on the landward slope with neither sediment cover nor ferromanganese hydro-oxide coatings; (4) abnormally close proximity of the Palau and Yap islands to the trench axis; (5) predominant distribution of barrier reefs in their western periphery apparently opposite to the easterly to northeasterly prevailing wind. © 2004 RAS.