HR: 0800h
AN: T21B-0584    [Abstracts]
TI: Role of Metamorphic Reactions and Related Density Changes in Mountain Building
AU: * Hetényi, G
EM: hetenyi@geologie.ens.fr
AF: Laboratoire de Géologie, ENS Paris, CNRS-UMR 8538, 24 rue Lhomond, Paris, 75005, France
AU: Godard, V
AF: Département de Sciences de la Terre, ENS Lyon, 46, allée d'Italie, 69364 Cedex 07, Lyon, France
AU: Cattin, R
AF: Laboratoire de Géologie, ENS Paris, CNRS-UMR 8538, 24 rue Lhomond, Paris, 75005, France
AU: Brunet, F
AF: Laboratoire de Géologie, ENS Paris, CNRS-UMR 8538, 24 rue Lhomond, Paris, 75005, France
AB: It is well known that the rocks of the crust experience a wide range of pressure and temperature conditions, especially in tectonically active zones. These conditions are registered by imprints of different petrological variations, and lead to the significant variations of density from low to high grade metamorphic facies. Here we use a 2-D finite element model, Cast3M, that was modified to incorporate metamorphic phase changes. The density of each element is derived from petrogenetical grids yielding density ρ as a function of temperature T and pressure P for a given composition, including thermal expansion and compressibility effects. To ensure local mass conservation, the exact density values are imposed in the model as volumetric variations, which are implemented using the tectonic stresses and the boundary conditions. The scheme is stabilized for different types of rheology, with elastic or non-linear visco-elastic behaviour. The numerical model is able to simulate convergence and to take into account erosion processes. We apply our model in a convergent context with an initial topography. The scale of the model is ~1000 km in length and ~150 km in thickness, including a mantle, a lower and an upper crustal layer. The duration of the convergence is in the order of a few million years. Our preliminary results show that density variations due to mineral phase changes can play an important role in mountain building processes. We suggest that deformation localization and topography evolution studies should account for realistic rheologies, erosion mechanisms, as well as metamorphic facies changes. In models where metamorphic reactions are not correctly implemented, the induced errors with regard to mass conservation and crustal deformation are significant.
DE: 3699 General or miscellaneous
DE: 8104 Continental margins: convergent
DE: 8108 Continental tectonics: compressional
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting