Open AccessOrigin of the Palau and Yap trench‐arc systems
Author(s) -
Kobayashi Kazuo
Publication year - 2004
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2003.02244.x
Subject(s) - geology , trench , asthenosphere , subduction , slab , convergent boundary , pacific plate , seismology , back arc basin , tectonics , oceanic crust , geophysics , chemistry , organic chemistry , layer (electronics)
SUMMARY 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.