Edge-driven convection along the Colorado Plateau - Great Basin Transition: Implications for the morphology and dynamics of the Plateau
Abstract
High mountains and extensive middle to late Cenozoic magmatism rim the margins of the Colorado Plateau (CP) resulting in a bowl-shaped morphology, with the interior of the CP being relatively unaffected by Laramide compression and Cenozoic extension and magmatism. We present new passive seismic imaging and modeling results from the RISTRA 1.0-1.5 transect across the CP that reveal ongoing crustal and uppermost mantle processes affecting the western CP and Great Basin (GB) transition. The CP crust exhibits variable thickness (42- 50 km) near its centre and thins gradually from 40 km to 30 km thick at the western edge, where the highest elevations and the roughest topography are also observed. However, isostatic calculations suggest that less than 50 percent of central CP elevations can be explained by thickened crust alone, with CP margins requiring nearly total mantle compensation. The responsible mechanism for margin topography is edge-driven convection in the upper mantle induced by a step in lithosphere thickness at the western edge of the CP. This step probably was created by the collapse of the enriched and weak Great Basin Phanerozoic lithosphere abutting the depleted and stronger Proterozoic CP lithosphere. In this interpretation, edge-driven convection results in upward flow of material below the transition zone and downward flow below the interior edge of the plateau. The mantle flow causes dynamic uplift of the transition zone and drives a progressive inward migration of Cenozoic volcanism at the CP edge of ~7 mm/yr. Horizontal flow velocities at the margins related to the convection cell are maximally 3 cm/yr at about 200 km depth. Downwelling below the CP interior may additionally influence the history of regional Colorado River system drainage and entrenchment. A similar process may have occurred during the opening of the Rio Grande Rift on the southeastern margin of the CP.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.T31E..07N
- Keywords:
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- 7218 Lithosphere (1236);
- 7270 Tomography (6982;
- 8180);
- 8103 Continental cratons;
- 8109 Continental tectonics: extensional (0905);
- 8121 Dynamics: convection currents;
- and mantle plumes