HR: 0800h
AN: U21A-0011    [Abstracts]
TI: Errors in modeling contraction, isostatic compensation and rock-mass balance in conductive cooling models of the oceanic lithosphere: Implications on Earth's power, radioactive contents, and convective style
AU: * Hofmeister, A M
EM: hofmeist@wustl.edu
AF: Dept. EPSc, Washington U., St. Louis, MO 63130, United States
AU: Criss, R E
EM: criss@wustl.edu
AF: Dept. EPSc, Washington U., St. Louis, MO 63130, United States
AU: Hamza, V M
EM: hamza@on.br
AF: 2Observatório Nacional, Rua General José Cristino, Rio de Janeiro, 77, Brazil
AB: High values of global power (44 TW) are derived from cooling models of the oceanic floor, which find support through their alleged prediction of seafloor depths. However, a factor of 3 error exists in equations used to predict depth as a function of seafloor age. These models allow for contraction only in z, which is governed by linear thermal expansivity (α_l), yet volumetric expansivity (α_v= 3α_l) has been erroneously used. Many additional problems exist in half-space and plate models: (1) Isostacy was considered, but rock-mass was not conserved, which means that subsidence as modeled, involves changing rock to water. (2) Contraction is based on infinitely high columns in the half-space model. (3) The half-space is assumed to start at z = d_w, which means that T(z) should depend on d_w but all such terms have been dropped. (4) Constant surface and constant basal temperatures are assumed, so the average temperature of the lithosphere cannot possibly change: thus, cooling or contraction is not permitted by model assumptions: the calculated contraction instead results from all these errors. These faulty 1-d models fit globally averaged depths only for seafloor ages < 60 My and only if basal temperature is ca 4000 K using reasonable values for the various physical parameters. This value is incompatible with mantle petrology, and predicts an excessive global power of >130 TW. Neither seafloor depths nor heat flux are represented by 1-d conductive cooling models. Instead of originating in contraction, subsidence actually results because mid-ocean ridges overlie hot mantle upwellings at the edge of convection cells, whereas old oceanic floor overlies colder mantle over the flanks of the convection cells. We show that upper mantle temperatures govern seafloor subsidence, suggesting layered convection.. Moreover, recent assessment of heat flow data, corrected for duplications and errors in location, limits global power to between 31+/-3 TW. This value is consistent with an enstatite chondrite model of the bulk silicate Earth, and does not require K or other substantial heat sources in the core. Known sequestering of most of the radioactives in the crust efficiently expels heat. Quasi-steady state is consistent with stratified convection.
DE: 1025 Composition of the mantle
DE: 5139 Transport properties
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8130 Heat generation and transport
SC: Union [U]
MN: 2007 Fall Meeting