HR: 0800h
AN: T31A-1268    [Abstracts]
TI: Convergence and Extension Driven by Gravitational Instability in Continental Orogens
AU: * Gemmer, L
EM: lykke@earth.leeds.ac.uk
AF: School of Earth and Environment, Leeds University, Leeds, LS29JT United Kingdom
AU: Houseman, G A
EM: greg@earth.leeds.ac.uk
AF: School of Earth and Environment, Leeds University, Leeds, LS29JT United Kingdom
AB: The mechanisms that drive the evolution of convergent continental orogens have been the research focus in many previous quantitative analyses of orogeny. One aspect that is still under much debate is the interplay of convergence and extension often observed in localized orogenic systems such as the Alboran Sea Basin and the Carpathian-Pannonian system. Extension often follows convergence but the spatio-temporal evolution is complex and in some cases extension is coeval with episodes of convergence in the surrounding orogenic belt. In several cases the extensional collapse of mountain belts is associated with dramatic thinning of the mantle part of the lithosphere, more so than the crust. Previous studies have shown that gravitational instabilities may play a fundamental role in the tectonics of mountain ranges. In general, the lithosphere is colder and thereby denser than the underlying asthenosphere. Under some circumstances this may cause the lithosphere to sink into the underlying asthenosphere. In this study we investigate how such gravitational instabilities may affect the evolution of continental orogens. The Alboran Sea and the Carpathian-Pannonian systems are both characterized by a roughly circular region of extension surrounded by arc-shaped mountain belts. Therefore we use axisymmetric finite element models to quantify the mechanisms that control the evolution of these systems. We investigate how parameters, such as density and viscosity (Newtonian or non-Newtonian) affect the evolution. In particular, we show how a crust initially thickened by localized convergence may promote lithospheric gravitational instabilities that cause the collapse of high topography and focused, depth-variable lithospheric thinning observed in the central basins of these regions.
DE: 8102 Continental contractional orogenic belts
DE: 8122 Dynamics, gravity and tectonics
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting