HR: 15:10h
AN: T32C-07    [PDF]
TI: Non-equilibrium temperatures and cooling rates in thick continental lithosphere
AU: * Michaut, C
EM: michaut@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75252 France
AU: Jaupart, C
EM: cj@ccr.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75252 France
AB: Beneath cratons, the lithosphere probably extends to more than 200km depth, which has important implications for the interpretation of heat flow measurements and xenolith geothermobarometry data. The time-scale for diffusive heat transport in a 200 km thick lid is about 1 Gy, which is smaller than, but comparable to, the half-lives of the main radiogenic isotopes of Uranium, Thorium and Potassium. In this case, the thermal structure of the lithosphere is not in equilibrium with the instantaneous rate of radiogenic heat generation and with the heat supply at the base of the lithosphere. For a given amount and distribution of heat sources, the instantaneous vertical temperature profile exhibits significant curvature and may be hotter than the steady-state prediction by as much as 150K. Comparison of (P,T) data with steady-state thermal models therefore leads to an overestimate of the mantle heat flow. The present-day rate of cooling in deep lithospheric material depends on the values of crustal and mantle heat production and on the rate of heat supply from the convecting mantle. Typical values of the cooling rate are in the range of 50-150 K/Gy, close to values reported by F. Albarede for xenoliths from South African kimberlites (Geophys. Res. Lett. 30, 1015, 10.1029/2002GL016484, 2003). Monte-Carlo calculations have been performed to investigate the range of values for the lithosphere thickness, mantle heat production and basal heat flux which are compatible with xenolith (P,T) arrays and surface heat flow determinations.
DE: 5134 Thermal properties
DE: 5418 Heat flow
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2003 Fall Meeting