HR: 08:45h
AN: MR31D-04    [Abstracts]
TI: High resolution mapping of Earth's deepest magma chamber: ultra-low velocity zones at the core mantle boundary
AU: * Rost, S
EM: s.rost@leeds.ac.uk
AF: University of Leeds, School of Earth and Environment Institute of Geophysics and Tectonics, Leeds, LS2 9JT, United Kingdom
AU: Garnero, E J
EM: garnero@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, United States
AU: McNamara, A
EM: mcnamara@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, United States
AU: Williams, Q
EM: qwilliams@es.ucsc.edu
AF: University of California Santa Cruz, Earth and Planetary Sciences Department 1156 High St, Santa Cruz, CA 95064, United States
AU: Stefan, W
EM: stefan@mathpost.la.asu.edu
AF: Arizona State University, Department of Mathematics and Statistics, Tempe, AZ 85287, United States
AB: Ultra-Low Velocity Zones (ULVZ) are seismically imaged enigmatic features at the core-mantle boundary (CMB). They are localized features characterized as thin layers (<40 km), with strong reductions in seismic velocities (up to 40%). Several seismic probes for ULVZ structure have been exploited, revealing strong evidence for ULVZ in a few isolated regions. Only about half of the area of the CMB has been seismically probed and many areas do not show any evidence for the presence of ULVZ. Lack of evidence for ULVZ structure either indicates that it is too small/thin (or mild in properties) to be detected with current seismic probes or that it is absent. High resolution seismic array studies reveal small ULVZ patches with scale lengths of a few hundred km's or less. They also show a rapid lateral transition from non-ULVZ mantle to ULVZ material. The seismic properties of ULVZ appear most consistent with partially molten material. Recent high resolution waveform studies also find evidence that the ULVZ material is denser than the surrounding mantle. Geodynamical calculations suggest that the ULVZ material can remain in distinct pockets even with large density increases that can exceed 10%. However, ULVZ viscosity plays an important role: if the ULVZ viscosity is significantly lower than the surrounding mantle, other mechanisms may be needed to keep ULVZ material in isolated pockets, and preventing it from flattening out on the CMB. Using a multidisciplinary approach, we study the existence, structure, and stability of ULVZs. We will present recent seismological evidence for ULVZ with seismic properties in agreement with the existence of dense partially molten material. New deconvolution processing techniques allow us to increase our resolution capabilities: we can now detect ULVZ layering down to about 2 km thickness. Using this method, we will present evidence for a previously undetected ULVZ structure east of Australia. High resolution geodynamical modeling shows that dense thermo-chemical piles (such as found beneath the central Pacific and southern Africa) might play an important role in ULVZ dynamics, including stabilizing ULVZ into lenses or ridges towards the perimeter edges of the piles. Seismological, mineral-physical and geodynamical evidence all point to the possibility of ULVZ being the deepest and largest magma chambers on Earth.
DE: 3618 Magma chamber processes (1036)
DE: 7207 Core (1212, 1213, 8124)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting