HR: 0800h
AN: T21C-0498    [Abstracts]
TI: Thermal-Chemical Model Of Subduction: Results And Tests
AU: * Gorczyk, W
EM: weronika.gorczyk@erdw.ethz.ch
AF: Geological Institute, Swiss Federal Institute of Technology, Sonneggstrasse 5 NO, Zurich, 8092 Switzerland
AU: Gerya, T V
EM: taras.gerya@erdw.ethz.ch
AF: Geological Institute, Swiss Federal Institute of Technology, Sonneggstrasse 5 NO, Zurich, 8092 Switzerland
AU: Gerya, T V
EM: taras.gerya@erdw.ethz.ch
AF: Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russian Federation
AU: Connolly, J A
EM: james.connolly@erdw.ethz.ch
AF: Geological Institute, Swiss Federal Institute of Technology, Sonneggstrasse 5 NO, Zurich, 8092 Switzerland
AU: Yuen, D A
EM: daveyuen@gmail.com
AF: Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minneapolis, MN 55455-0219 United States
AU: Rudolph, M
EM: maxwellr@gmail.com
AF: Oberlin College, Oberlin, Ohio, 44074 United States
AB: Seismic structures with strong positive and negative velocity anomalies in the mantle wedge above subduction zones have been interpreted as thermally and/or chemically induced phenomena. We have developed a thermal-chemical model of subduction, which constrains the dynamics of seismic velocity structure beneath volcanic arcs. Our simulations have been calculated over a finite-difference grid with (201×101) to (201×401) regularly spaced Eulerian points, using 0.5 million to 10 billion markers. The model couples numerical thermo-mechanical solution with Gibbs energy minimization to investigate the dynamic behavior of partially molten upwellings from slabs (cold plumes) and structures associated with their development. The model demonstrates two chemically distinct types of plumes (mixed and unmixed), and various rigid body rotation phenomena in the wedge (subduction wheel, fore-arc spin, wedge pin-ball). These thermal-chemical features strongly perturb seismic structure. Their occurrence is dependent on the age of subducting slab and the rate of subduction.
The model has been validated through a series of test cases and its results are consistent with a variety of geological and geophysical data. In contrast to models that attribute a purely thermal origin for mantle wedge seismic anomalies, the thermal-chemical model is able to simulate the strong variations of seismic velocity existing beneath volcanic arcs which are associated with development of cold plumes. In particular, molten regions that form beneath volcanic arcs as a consequence of vigorous cold wet plumes are manifest by > 20% variations in the local Poisson ratio, as compared to variations of ~ 2% expected as a consequence of temperature variation within the mantle wedge.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8033 Rheology: mantle (8162)
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: Fall Meeting 2005