Thermal and chemical variations in subcrustal cratonic lithosphere: Evidence from crustal isostasy

LITHOS
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Abstract

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 crust. 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 °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.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Thermal and chemical variations in subcrustal cratonic lithosphere: Evidence from crustal isostasy
Series title LITHOS
DOI 10.1016/j.lithos.2003.07.004
Volume 71
Issue 2-4
Year Published 2003
Language English
Publisher Elsevier
Contributing office(s) Earthquake Science Center
Description 9 p.
First page 185
Last page 193
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