HR: 14:55h
AN: T23E-06 INVITED    [Abstracts]
TI: Modeling Three-dimensional Variations in Mantle Flow due to Rollback Subduction and Back- arc Extension: Implications for Arc Magmagenesis
AU: * Kincaid, C
EM: kincaid@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, South Ferry Rd., Narragansett, RI 02882, United States
AU: Druken, K
EM: kdruken@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, South Ferry Rd., Narragansett, RI 02882, United States
AU: Griffiths, R W
EM: ross.griffiths@anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 2605, Australia
AU: Foden, J
EM: john.foden@adelaide.edu.au
AF: Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia
AB: Circulation and melting of the mantle are directly related to large-scale plate motions. We use laboratory experiments to characterize how subduction of a discrete plate segment and extension in an overriding plate influence 3D return flow trajectories to the sub-arc mantle wedge and spatial-temporal heterogeneity in slab and wedge temperature fields. Our goal is to identify which combinations of subduction parameters favor either decompression melting, slab melting or melting of the hydrated slab boundary layer due to vertical advection. Models utilize a glucose working fluid with a temperature dependent viscosity to represent the upper 2000km of the mantle. The subducting plate is modeled with a Phenolic sheet and extension in the overriding plate is produced using Mylar sheets. We recreate basic subduction styles observed in previous dynamic subduction models using simplified, kinematic forcing. Slab plate segments, driven by hydraulic pistons, move with various combinations of downdip, rollback and steepening motion. Two modes of producing back-arc extension (1. trench retreat vs. 2. overriding plate retreat) are investigated. Models reveal strong vertical shear within the wedge produced by lateral return flow around the retreating slabs and coupling between the wedge fluid and the overriding plate. Results show that vertical velocities in the wedge (e.g., favorable to decompression melting) and both slab and wedge temperatures are strongly related to the mode of back-arc extension, the ratio of rollback to downdip motion and the degree of plate steepening. Mode 1(2) back-arc spreading produces laterally heterogeneous (homogeneous) temperature distributions in the slab and beneath the spreading center. Experiments predict rapid onset, short-lived periods of slab-influenced melting after the initiation of slab rollback and back-arc extension due to direct vertical advection of material from the hydrous boundary layer above the downgoing slab.
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: 8178 Tectonics and magmatism
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting