HR: 08:30h
AN: DI41B-03    [Abstracts]
TI: Ubiquitous Low-Velocity Layer Atop the 410-km Discontinuity Beneath the Northern Rocky Mountains
AU: Dueker, K
EM: dueker@uwyo.edu
AU: * Jasbinsek, J J
EM: johnjj@uwyo.edu
AF: University of Wyoming Dept. of Geology & Geophysics, 1000 University Avenue, Laramie, WY 82071, United States
AB: The 410-water-filter model is a provocative new model which predicts that a spatially localized layer of hydrous partial may pool atop the 410-km discontinuity ("410") as a result of the difference in water solubility between the mantle transition zone and the overlying upper mantle [Bercovici and Karato, 2003]. If the transition zone is sufficiently hydrated then upwelling mantle crosses the wet-olivine solidus and produces a hydrous partial melt. The density of this partial may be intermediate to that of the uppermost transition zone and deep upper mantle causing the melt to pond atop the 410. The model suggests that decoupling of incompatible elements into the melt dynamically creates MORB and OIB geochemical signatures obviating the need for pre-existing chemical reservoirs. Details of the 410-water-filter and its potential operation are the source of much debate and research [Hirschmann et al., 2006; Karato et al., 2006; Leahy and Bercovici, 2007]. However, a small number of seismic observations detect a low-velocity layer above the 410 and are interpreted as a manifestation of the 410-water filter [Song & Helmberger, 2004; Gao et al., 2006; Vinnik et al., 2003, 2004]. More recently a ubiquitous low velocity layer was detected with P-S receiver functions atop the 410 beneath three dense PASSCAL arrays in the northern Rocky Mountains, with the data requiring a 22-km thick layer with an 8.9% shear velocity reduction and sharp (<6.4 km) top gradient [Jasbinsek and Dueker, 2007]. Here we report observations of a similar low velocity layer atop the 410 beneath the RISTRA and CD-ROM arrays in the southern Rocky Mountains. Velocity modeling with this data does not significantly differ from previous results, implying a coherent structure to the melt layer atop the 410 beneath the Rocky Mountains.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 7203 Body waves
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting