HR: 0830h
AN: U51B-0019    [PDF]
TI: Excess Temperature and Heat Transport in Mantle Plumes: a reassessment
AU: * Bunge, H
EM: bunge@lmu.de
AF: Hans-Peter Bunge, Dept of Geo and Envt Sciences, Ludwig Maximilians University Munich, Theresienstrasse 41, Munich, D-80333 Germany
AB: Heat transfer across the core mantle boundary (CMB) is fundamentally important to Earth's internal energy budget, but the amount of heat entering the mantle from the core is poorly known. Classic arguments based on the dynamic topography over mantle hotspots suggest a rather modest core contribution to the mantle energy budget, on the order of 5-10 percent. Recent geodynamic studies, however, favor significantly higher values to overcome the problem of insufficient mantle heat sources, and to satisfy constraints on the power requirements of the geodynamo and estimates of the thermal history of the core. Here we use a high resolution mantle circulation model to explore the evolution of excess temperature in hot upwelling plumes that rise against mantle flow with substantial internal heat generation. We use the 3D spherical mantle dynamics code TERRA implemented on a dedicated network of PCs to achieve spatial resolutions of less than 50 km throughout the mantle, sufficient to resolve highly time-dependent convection at Rayleigh numbers based on internal heating that exceed 10exp8. We explore three relatively simple mantle circulation models having 5, 15, and 45 percent core heating respectively, all of which include a realistic depth variation of thermodynamic parameters following a Murnaghan EOS, as well as a substantial depthwise increase in mantle viscosity. We find the non-adiabatic mantle geotherm, which arises from internal mantle heat generation, has a dramatic effect in lowering the excess temperature of hot upwelling plumes, and in systematically decreasing plume temperatures relative to ambient mantle from the CMB to the surface. This non-adiabatic effect may provide some explanation for unusually low plume excess temperatures inferred from the petrology and isotope geochemistry of hotspot lavas, and we speculate that our results could imply that current estimates on the core heatflux based on hotspot topography should be increased by perhaps a factor of three.
DE: 8105 Continental margins and sedimentary basins
DE: 8115 Core processes (1507)
DE: 8120 Dynamics of lithosphere and mantle--general
SC: U
MN: 2003 Fall Meeting