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New seismic-geodynamic-mineral physical constraints on heat flux at the core-mantle boundary: Implications for the importance of active hot thermal plumes

22/10/2009

IPGP - Campus Jussieu

16:00

Séminaires généraux de l’IPGP

Salle Bleue

Alessandro Forte

Universite du Quebec a Montreal

Resume: Mantle dynamics and thermal evolution is strongly dependent on the relative contributions from internal heating (due to radioactivity and secular cooling) and from bottom heating across the core-mantle boundary (CMB). In particular, the relative importance of active, thermally buoyant upwellings and mantle cooling due to descending lithospheric plates is controlled by the amplitude of heat flux across the CMB. I will present a new constraint on CMB heat flux derived from tomography-based convection models that incorporate lateral variations in mantle temperature provided by global seismic and geodynamic data sets, in which mineral physical constraints on mantle thermal heterogeneity are also imposed (Simmons et al. 2009). These convection calculations employ inferences of depth-dependent, horizontally averaged mantle viscosity derived from joint inversions of glacial isostatic adjustment and mantle convection data (Forte and Mitrovica 2004). I employ this tomography-geodynamics based mantle convection model to explore the convective transport of mass (buoyancy flux) and heat (advected heat flux) across the lower and upper mantle. Predictions of advected heat flux at the top of the seismic D" layer provide direct constraints on the heat flux across the core-mantle boundary (CMB). The estimated present-day CMB heat flux is in excess of 10 TW. I also show the implications for the present-day distribution of secular heating and cooling at different depths in the mantle. -------------------------------------------------------------------------------- Séminaires généraux de l'Institut de Physique du Globe de Paris --------------------------------------------------------------------------------