HR: 08:00h
AN: T31A-01 INVITED     [PDF]
TI: Constructing a dynamically and geologically consistent hypothesis for the initiation of Izu-Bonin-Mariana subduction
AU: * Hall, C E
EM: chall@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology MS 252-21, Pasadena, CA 91024
AU: Gurnis, M
EM: gurnis@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology MS 252-21, Pasadena, CA 91024
AU: Lavier, L L
EM: luc@utig.ig.utexas.edu
AF: Institute for Geophysics Jackson School of Geosciences University of Texas at Austin, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759-8500
AB: The Izu-Bonin-Mariana (IBM) subduction zone, though now mature, is an excellent location for studying intra-oceanic subduction initiation largely because drilling of its fore-arc basement provides constraints on the tectonic and magmatic history during initiation. The timing of uplift and subsidence of the overriding plate, recorded on topographic ridges of the West Philippine Basin, constrain the strength of interplate coupling during initiation. Arc volcanism during the first ~10 My of subduction at IBM occurred at a rate much higher than typical of mature arcs, and over an area that was exceptionally broad (~200 km) compared to present arcs (~50 km in width). The early arc was dominated by boninitic volcanism, uncommon in mature arcs, as it requires a high degree of partial melting of a clinopyroxene-poor source that is depleted in basaltic components (but presumably enriched in volatiles) and lies on an abnormally steep geothermal gradient. We are studying the dynamics of subduction initiation with numerical methods that allow for simultaneously modeling multiple styles of deformation, from elastic plate bending to plastic failure at plate boundaries to viscous flow in the deeper mantle. Our methods allow us to address the previously studied problem of determining the magnitude of driving and resisting forces in unprecedented detail, and to monitor the evolution of these interacting forces. Perhaps more importantly, though, we are developing means for extracting a variety of predicted constraints from these models, such as topography, gravity, and melting characteristics. With such model predictions, we will address whether the unique character of early IBM volcanism a general feature of incipient subduction, or whether extenuating circumstances, such as the influence of a mantle plume, are required to explain the observations.
DE: 3210 Modeling
DE: 8045 Role of fluids
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8125 Evolution of the Earth
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting