HR: 0830h
AN: T31D-0866    [PDF]
TI: Thermal and Chemical Variations in Subcrustal Cratonic Lithosphere: Evidence from Crustal Isostasy
AU: * Mooney, W D
EM: mooney@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Vidale, J E
EM: vidale@ess.ucla.edu
AF: UCLA, Earth and Space Sciences, Los Angeles, CA 90095 United States
AB: The Earth's topography at short wavelengths results from active tectonic processes, whereas at long wavelengths it is largely determined by isostatic adjustment for the density and thickness of the lithosphere. Using a global crustal model, we estimate the long-wavelength topography that is not due to crustal isostasy. Our most important finding is that cratons are generally depressed by 300 to 1500 m in comparison with predictions from pure crustal isostasy. We conclude that either: (1) cratonic roots may be 50 to 300 \deg C colder than previously suggested by thermal models, or; (2) cratonic roots may be, on average, less depleted than suggested by studies of shallow mantle xenoliths. Alternatively, (3) some combination of these conditions may exist. The thermal explanation is consistent with recent geothermal studies that indicate low cratonic temperatures, as well as seismic studies that show very low seismic attenuation at long periods (150 s) beneath cratons. The petrologic explanation is consistent with recent studies of deep ($>$140 km) mantle xenoliths from the Kaapvaal and Slave cratons that show 1-2% higher densities compared with shallow ($<$140 km), highly depleted xenoliths.
DE: 7218 Lithosphere and upper mantle
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8125 Evolution of the Earth
SC: Tectonophysics [T]
MN: 2003 Fall Meeting