HR: 0800h
AN: T41C-1220    [Abstracts]
TI: Bathymetry of Mariana Trench-Arc System and Formation of the Challenger Deep as a Consequence of Weak Plate Coupling
AU: * Gvirtzman, Z
EM: zohar@gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhei Yisrael Street, Jerusalem, 95501 Israel
AU: Stern, R J
EM: rjstern@utdallas.edu
AF: Geosciences Department, University of Texas at Dallas, Box 830688, 2601 N. Floyd Rd., Richardson, TX 75083-0688 United States
AB: The Challenger Deep in the southernmost Mariana Trench (western Pacific Ocean) is the deepest point on the earth's surface (10,920 m below sea level). Its location within a subduction trench, where one plate bends and descends below another, is not surprising. However, why is it located in the southernmost Mariana Trench and not at its central part, where the rate of subduction is higher, where the lithosphere is the oldest (and densest) on Earth, and where the subducted lithosphere pulling down is the longest in Earth (~1000 km or more according to seismic tomography)? We suggest that although subduction rate and slab age generally control trench depth, here, the width of the Plate Coupling Zone is more important and counteracts trench deepening. Beneath the central Marianas the subducted slab is attached to the upper plate along a 150-km-wide surface that holds the shallow portion of the subducted plate nearly horizontal, in spite of its great load and, thus, counters trench deepening. In contrast, along the south Mariana Trench the subducted length of the lithosphere is much shorter, but its attachment to the upper plate is only along a relatively narrow, 50-km-wide, surface. In addition, a tear in the slab beneath this region helps it to sink rapidly through the mantle and this combination of circumstances allows the slab to roll back, steepen, and form the deepest trench on Earth. In a wider perspective, the interrelations shown here between trench deepening, ridge shallowing, slab steepening, and forearc narrowing may shed light on other subduction zones located near edges of rapidly retreating slabs.
DE: 8180 Tomography
DE: 7230 Seismicity and seismotectonics
DE: 8122 Dynamics, gravity and tectonics
DE: 8123 Dynamics, seismotectonics
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting