HR: 1340h
AN: T53A-1410    [Abstracts]
TI: Modeling the role of back-arc spreading in controlling 3-D circulation and temperature patterns in subduction zones
AU: * Kincaid, C
EM: kincaid@gso.uri.edu
AF: Univ. of Rhode Island-Oceanography, South Ferry Rd., Narragansett, RI 02882 United States
AB: Subduction of oceanic lithosphere provides a dominant driving force for mantle dynamics and plate tectonics, and strongly modulates the thermal evolution of the mantle. Magma generation in arc environments is related to slab temperatures, slab dehydration/wedge hydration processes and circulation patterns in the mantle wedge. A series of laboratory experiments is used to model three-dimensional aspects of flow in subduction zones, and the consequent temperature variations in the slab and overlying mantle wedge. The experiments utilize a tank of glucose syrup to simulate the mantle and a Phenolic plate to represent subducting oceanic lithosphere. Different modes of plate sinking are produced using hydraulic pistons. The effects of longitudinal, rollback and slab-steepening components of slab motions are considered, along with different thicknesses of the over-riding lithosphere. Models look specifically at how distinct modes of back-arc spreading alter subduction zone temperatures and flow in the mantle wedge. Results show remarkably different temperature and circulation patterns when spreading is produced by rollback of the trench-slab-arc relative to a stationary overriding back-arc plate versus spreading due to motion of the overriding plate away from a fixed trench location. For rollback-induced spreading, flow trajectories in the wedge are shallow (e.g., limited upwelling), both the sub-arc and back-arc regions are supplied by material flowing around the receding slab. Flow lines in the sub-arc wedge are strongly trench-parallel. In these cases, strong lateral variations in slab surface temperature (SST) are recorded (hot at plate center, cool at plate edge). When the trench is fixed in space and spreading is produced by motion of the overriding plate, strong vertical flow velocities are recorded in the wedge, both the shallow sub-arc and back-arc regions are supplied by flow from under the overriding plate producing strong vertical shear. In these cases SSTs are nearly uniform across the plate. Results have implications for geochemical and seismic models of 3-D flow in subduction zones influenced by back-arc spreading, such as the Marianas.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 3001 Back-arc basin processes
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: Fall Meeting 2005