HR: 10:50h
AN: MR22A-03 INVITED     [Abstracts]
TI: Superadiabaticity of the lowermost part of the mantle thermally controlled by the post-perovskite phase transition
AU: * Yuen, D A
EM: davey@krissy.geo.umn.edu
AF: University of Minnesota, 310 Pillsbury Dr SE Dept. of Geology and Geophysics, Minneapolis, MN 55455-0219 United States
AU: Monnereau, M
EM: marc.monnereau@cnes.fr
AF: CNRS, Observatoire Midi-Pyrenees, 14 avenue E. Belin, Toulouse, 314000 France
AB: There is increasing evidence of superadiabaticity in the lowermost portion of the mantle, from 500 to 700 km above the core-mantle boundary, from both seismology ( e.g Cammarano et al., 2005 ) and mineral physics ( e.g. da Silva et al, 2000 ). This may be caused by a blanketing effect due to a dense chemical layer ( e.g. Kellogg et al., 1999) or an accumulation of recycled crust ( Coltice and Ricard, 1999). The temperature-dependence of radiative thermal conductivity may also contribute to this superadiabatic state ( van den Berg et al., 2004 ). We have found also the post-perovskite( PPV) phase transition may also be a contributor to this phenomenon. From 3-D spherical-shell anelastic compressible convection including a deep phase change, the PPV, we have demonstrated that as long as the CMB temperature, T-cmb is higher than the temperature intercept of the PPV at the CMB pressure , T-i, the horizontally averaged temperature gradient in the the thermal boundary layer is equal to the Clapeyron slope of the PPV i.e. 6.25 K/km for a Clapeyron slope of 8 MPa/K, which corresponds to a core heat-flux of around 5 TW. This superadiabatic effect disappears, as soon as the CMB temperature becomes lower than T-i, due to secular cooling. This phenomenon is restricted to a range of temperature of above T-i. We have found that T-cmb can be as high as 4000 K for this superadiabatic condition to prevail. Such a phenomenon would prevent a double-crossing of the phase change by the horizontally averaged temperature profile, as proposed by Hernlund et al. ( 2005), at least in the range of the physical parameters of PPV transition , as measured by laboratory experiments and derived by ab initio calculations ( Tsuchiya et al., 2004 )
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005