HR: 11:05h
AN: T32A-04    [Abstracts]
TI: Geophysical Evidences for Chemical Variations in the Australian Continental Mantle
AU: van Gerven, L
EM: gerven@geo.uu.nl
AF: Utrecht University, Budapestlaan 4, PO Box 80021, Utrecht, 3508 TA Netherlands
AU: * Deschamps, F
EM: deschamp@geo.uu.nl
AF: Utrecht University, Budapestlaan 4, PO Box 80021, Utrecht, 3508 TA Netherlands
AU: van der Hilst, R D
EM: hilst@mit.edu
AF: Utrecht University, Budapestlaan 4, PO Box 80021, Utrecht, 3508 TA Netherlands
AU: van der Hilst, R D
EM: hilst@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: The relative density-to-shear velocity scaling ($\zeta$) provides a diagnostic for the presence of compositional variations in the mantle. We invert shear-wave velocity from the recent 3-D model AUS04-Vs and gravity anomalies EGM96 for radial profiles of $\zeta$ of the uppermost mantle beneath Australia. We performed calculations for the three major tectonic provinces that constitute the continent, and found significant differences between them. The $\zeta$ profile for the Phanerozoic region can be explained by thermal variations alone. In contrast, negative values of $\zeta$ suggest that variations in composition are important between $\sim$75 and $\sim$150 km depth in the Proterozoic continental lithosphere (central Australia). It is likely that chemical variations are also required to explain our inferences for the Archean craton (west Australia), but poor tomographic resolution precludes a definitive conclusion. The scaling factors found are consistent with chemical depletion of deep Precambrian lithosphere, which supports a tectosphere model for the Australian continental roots.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7215 Earthquake parameters
DE: 1212 Earth's interior--composition and state (8105)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting