HR: 0800h
AN: T41E-1348    [Abstracts]
TI: Effects of Plate Boundary Migration on Mantle Dynamics of Oceanic Triple Junctions
AU: * Georgen, J
EM: georgen@gly.fsu.edu
AF: Florida State University, Department of Geological Sciences, Tallahassee, FL 32306 United States
AB: This study investigates characteristics of mantle flow, thermal structure, and melting around an oceanic ridge-ridge-ridge (RRR) triple junction. RRR triple junctions mark the location of unique upwelling conditions along the global mid-ocean ridge system, and mantle dynamics are predicted to be significantly different than the case where only two plates diverge. An earlier study (Georgen and Lin, EPSL 2002) focused on predicting mantle flow and temperature patterns around a triple junction with geometry similar to the Rodrigues Triple Junction in the central Indian Ocean. The Rodrigues Triple Junction is comprised of the ultra-slow-spreading Southwest Indian Ridge and the intermediate-spreading Central and Southeast Indian ridges. Using a three-dimensional finite element model, Georgen and Lin suggested the following results: (1) The upwelling velocity and temperature along the slowest-spreading branch were calculated to increase toward the triple junction, approaching the greater upwelling rate and higher temperature of the fastest-spreading Southeast Indian Ridge branch. In contrast, the velocity and thermal fields for the fastest-spreading ridge were not significantly different from the case of a single ridge with the corresponding spreading rate. (2) Upwelling velocity along the Southwest Indian Ridge was predicted to increase more than threefold within 200 km of the triple junction. A strong component of along-axis flow, directed away from the triple junction, was also predicted, as were temperature increases of approximately 75^oC at depths within the partial melting zone. The investigation of Georgen and Lin (2002) fixed the triple junction point in the middle of the model domain, driving mantle flow by the divergence of three surface plates. In this sense, it was a relative plate motion study. However, triple junctions migrate with respect to the absolute plate motion reference frame, and this migration adds an additional component of flow to the three-dimensional nature of upwelling. This study incorporates triple junction migration into a three-dimensional finite element numerical model, and contrasts new model predictions with the earlier results derived with the triple junction fixed to the absolute plate motion reference frame. We also comment on the implications of triple junction migration for the melting history of mantle parcels cycled through the triple junction system.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005