The Weakening of Lithospheric Fault Zones
Abstract
Large-scale lithosphere fault zones are seen to be extremely weak with respect to the country rocks and the sismogenic crust mainly controls their strength. In opposite, regions of low strain have a high strength, mainly controlled by the sub-continental mantle. The existence and causes of this weakness remain to be understood and are a matter of debate. Geological studies of exhumed deformed fault zone allow us to constrain dominant deformation mechanisms during lithosphere deformation: reaction weakening in the middle crust and grain size reduction controlled by grain-boundary sliding in the sub-continental mantle. On these bases, transient lithosphere rheologies are proposed and likely predict significant strength decrease during lithosphere deformation. 2D large strain numerical models at lithosphere scale are then presented in order to constrain the mechanics of lithosphere fault zone weakening. The weak mantle strength predicted beneath deforming regions from geological and geophysical data could therefore be a consequence of both long-term deformation (≥ Myr) and large-scale strain localization, and might not only reflect a steady-state strength of the lithosphere.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T41B2137G
- Keywords:
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- 1236 GEODESY AND GRAVITY / Rheology of the lithosphere and mantle;
- 3902 MINERAL PHYSICS / Creep and deformation;
- 8031 STRUCTURAL GEOLOGY / Rheology: crust and lithosphere;
- 8111 TECTONOPHYSICS / Continental tectonics: strike-slip and transform