HR: 0800h
AN: U11A-0009    [Abstracts]
TI: Time Variability in Cenozoic Reconstructions of Mantle Heat Flow: Plate Tectonic Cycles and Implications for Earth's Thermal Evolution
AU: Loyd, S J
EM: loyd@usc.edu
AF: University of Southern California, Department of Earth Sciences, Los Angeles, CA 90089, United States
AU: Becker, T W
EM: twb@usc.edu
AF: University of Southern California, Department of Earth Sciences, Los Angeles, CA 90089, United States
AU: * Conrad, C P
EM: conrad@jhu.edu
AF: Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD 21218, United States
AU: Lithgow-Bertelloni, C
EM: crlb@umich.edu
AF: University College London, Department of Earth Science, London, WC1E6BT, United Kingdom
AU: Corsetti, F A
EM: fcorsett@earth.usc.edu
AF: University of Southern California, Department of Earth Sciences, Los Angeles, CA 90089, United States
AB: The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by ~ 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 5418 Heat flow
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8125 Evolution of the Earth (0325)
DE: 8130 Heat generation and transport
SC: Union [U]
MN: 2007 Fall Meeting