Physical Structure of the Continental Lithosphere
The role of continents in mantle dynamics is poorly understood. In order to improve this we need good constraints on the thermo-chemical structure of continental lithosphere. We have been working on characterizing this from seismic models, which yield the most comprehensive images of continental structure, complemented by surface heat flow data and published constraints on geothermobarometry in regions where xenoliths have been found. We document a very wide range in lithospheric temperatures which require, besides variations in crustal heat production, variable lithosphere-mantle interaction. From the models we have used (with lateral resolution on the order of 100-200 km) there is little evidence of the presence of melt.
This figure shows temperatures at 110 km depth estimated from the S-velocity model NA00 of Van der Lee et al. (2001. Estimated uncertainties due to the velocity-temperature conversion are +/- 100 degrees. The map shows an up to 1000 degree contrast in the shallow mantle below the western and eastern U.S. These temperatures are compatible with those inferred from P-velocities (Bijwaard et al., 1998 and Dueker 2000) and surface heat flow values. Western U.S. topography can be largely attributed to high shallow mantle temperatures and crustal structure. In the eastern U.S. compositional variations must affect lithospheric buoyancy. From Goes and Van der Lee (2002).
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Chris Hieronymus (Uppsala), Suzan van der Lee (Northwestern), Jolante van Wijk (Los Alamos), Jeroen van Hunen (Durham), Jeroen Ritsema (Univ. Michigan, Ann Arbor)