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Yvette, Here is what we wrote in Rey et al., 2001 with regard to gravitational collapse (sorry for self-referencing, but the paper I wrote are the ones I know the best!): "..we propose that the concept of gravitational collapse sensu stricto can be defined as the gravity-driven ductile flow that effectively reduces lateral contrasts in gravitational potential energy. Applied to a region with an excess of gravitational potential energy, this flow will drive extension following a phase during which gravitational potential energy has been stored. In contrast, gravity-driven flow will drive contractional deformation in regions having a deficit in gravitational potential energy with respect to their surroundings." Following this definition, gravitational collapse is expected to continue until the gravitational potential energy stored in the orogenic crust is totally consummed. The velocity at which this will occur is a function of the rheology of the orogenic belt (its ability to flow) and of the boundary conditions. I agree that "gravitational collapse" should not be confused with gravity-driven flow of orogenic belts to form orogenic plateaux in which case there is no net thinning of the orogenic belt but lateral redistribution of the orogenic material (Vanderhaeghe and Teyssier, 2001; Vanderhaeghe et al. GJI 2003 and references therein). It should neither be confused with syn-orogenic extension associated with extrusion and tectonic accretion of tectonic units forming orogenic belts (Vanderhaeghe, 2009, Vanderhaeghe in press). These distinct processes are not always easy to distinguish in natural data. Combining metamorphic petrology, structural geology and geochronology of exhumed deep-seated rocks with the analysis of sedimentary rocks, one can try to reconstruct the thermal-mechanical and topographic evolution of orogenic belts and discuss which of the previous scenarii was at play. This is the price to pay! Good luck! Olivier. Note : I can send the pdf versions of the papers quoted above if required. Le 09/12/2011 04:39, Yvette Kuiper a écrit : > Dear experts and creative thinkers, > > In my Thursday evening ponderings I am wondering how long orogenic > collapse can continue after convergence ends. 10 Ma? 50 Ma? What makes > orogenic collapse continue for a longer time (e.g., size of orogen, > certain tectonic settings)? Do we know? Any good examples? Ideas? I'd > love to hear. > (not talking about crustal extension that follows orogeny in some > places, but solely collapse as a result of the crustal thickening) > > I'm hoping for a fruitful discussion! > Cheers, Yvette > -- Olivier VANDERHAEGHE Professeur Dpt Geosciences Geologie et Gestion des Ressources Minerales et Energetiques Faculte des Sciences et Technologies Universite de Lorraine BP 239, 54506 Vandoeuvre les Nancy France +33 (0) 3 83 68 47 34 http://www.geologie.uhp-nancy.fr/Php/index.php http://www.g2r.uhp-nancy.fr/annuaire/vanderhaeghe.html