HR: 16:30h
AN: T24B-03    [Abstracts]
TI: Thermal modeling of the central Alaska subduction zone
AU: * van Keken, P
EM: keken@umich.edu
AF: University of Michigan, Department of Geological Sciences 425 East University Avenue, Ann Arbor, MI 48109-1063 United States
AU: Abers, G
EM: abers@bu.edu
AF: Boston University, Department of Earth Sciences 685 Commonwealth Avenue, Boston, MA 02215 United States
AU: Kneller, E
EM: ekneller@umich.edu
AF: University of Michigan, Department of Geological Sciences 425 East University Avenue, Ann Arbor, MI 48109-1063 United States
AB: The Pacific plate subducts beneath southern Alaska and produces most of the features commonly associated with subduction, including great earthquakes at shallow depths, intermediate-depth earthquakes to 150 km, a seismically slow mantle wedge, and upper-plate deformation. However, volcanism is virtually absent along the eastern 350 km of the subduction zone. This may be because temperatures in the mantle wedge are unusually low or because the slab does not devolatalize. The recent BEAAR broadband seismic experiment provided high-resolution images of the slab and wedge beneath central Alaska. These images provide some of the best constraints anywhere on the geometry of subduction at depth and the thermal state of the mantle wedge. Receiver functions show the top of the subducting plate to 150 km depth as a low-velocity channel, relative to surrounding mantle. To achieve such low velocities the subducting crust must not convert to eclogite, perhaps because it remains too cool to do so. Intraslab seismicity lies inside the low-velocity channel and gradually migrating from its top to bottom, suggestive of a dehydration isotherm stepping into the slab as it warms. Attenuation tomography shows that the overlying wedge is warm as other subduction zones. This subduction zone is also notable for its unusually shallow dip through the thrust zone. We developed a thermal model of this subduction zone using the geometry determined by the seismic experiment with a non-Newtonian rheology in the dynamic and a 50 km thick rigid lithosphere on top of the wedge. The hypocenters follow the 600 C contour predicted from our model. Below 150 km temperatures become high enough to allow for the conversion to eclogite and the hottest part of the wedge extends not closer than 450 km from the trench. This suggests that the characteristics of the central Alaska subduction zone can be satisfactorily explained by thermal models similar to those in Honshu and Cascadia (e.g., Van Keken et al., Gcubed, 2001) without invoking a special role for subduction zone fluids.
DE: 7230 Seismicity and seismotectonics
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting