HR: 0800h
AN: U41A-0704    [Abstracts]
TI: Is a pyrolitic adiabatic mantle compatible with seismic data?
AU: Cammarano, F
EM: fabio@tomo.ig.erdw.ethz.ch
AF: ETH Zurich, Switzerland, Institute of Geophysics ETH Hoenggerberg (HPP), Zurich, CH-8093 Switzerland
AU: Goes, S
EM: saskia@tomo.ig.erdw.ethz.ch
AF: ETH Zurich, Switzerland, Institute of Geophysics ETH Hoenggerberg (HPP), Zurich, CH-8093 Switzerland
AU: * Deuss, A
EM: deuss@esc.cam.ac.uk
AF: Cambridge University, U.K., Univ Cambridge Dept. Earth Sciences Bullard Labs Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Giardini, D
EM: giardini@sed.ethz.ch
AF: ETH Zurich, Switzerland, Institute of Geophysics ETH Hoenggerberg (HPP), Zurich, CH-8093 Switzerland
AB: We test the simplest average physical model of a mantle convecting as a whole (i.e., following an adiabatic temperature gradient) with a single composition with phase transitions (pyrolite) directly against global seismic data, instead of against spherically symmetric seismic models. Although the seismic models have significant uncertainties, looking at the data reveals some very strong constraints which are hard to reconcile with an adiabatic pyrolitic mantle, given the current state of knowledge of elastic and anelastic mineral parameters and their extrapolation to high pressure and temperature. This physical model generally gives (a) a stronger baseline offset between upper and lower mantle average travel-time residuals than allowed by the data and (b) an insufficient decrease in velocity gradient with depth in the deeper lower mantle (above 2500 km). 10$^5$ upper and 10$^5$ lower mantle models selected randomly within the mineral physics parameter uncertainties were tested. Only 2 lower mantle models and 24 upper mantle models yield whole mantle seismic structures that are compatible with global ISC P and S travel times and central frequencies of toroidal and spheroidal fundamental modes with angular order higher than 18. To improve the fit to the seismic data, the physical model would require (a) a lower velocity transition zone composition than dry pyrolite (at least around continents and subduction zones) as well as (b) a gradual change in physical state of the lower mantle that decreases the velocity-depth gradient, e.g., a superadiabatic temperature increase.
DE: 7207 Core and mantle
DE: 3909 Elasticity and anelasticity
DE: 1212 Earth's interior--composition and state (8105)
SC: Union [U]
MN: 2004 AGU Fall Meeting