The Effects of Gravitational Instability on the Tectonic Evolution of Continental Orogens
Abstract
Convergent continental orogens have been the research focus of numerous geological and geophysical surveys and dynamical modeling studies, but the mechanisms controlling the evolution of these systems are still under debate. The temporal and spatial distribution of tectonic processes in orogenic regions is complex, and the interplay between buoyancy forces and regional tectonics in some of these systems is still not well understood. 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. A key region for investigating these processes is the Carpathian-Pannonian system of eastern Europe, where rapid extension took place in the Pannonian Basin simultaneously with contractional deformation in the surrounding orogens. Previous studies show 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. We use dynamic numerical models to investigate how such gravitational instabilities may affect the evolution of continental orogens. 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 developing simultaneously with contractional deformation and lithospheric downwelling in the adjacent areas. We investigate the relative importance of buoyancy and regional tectonics in convergent continental orogens and show how density and viscosity (Newtonian or non-Newtonian) affect the evolution of a model system. We investigate the distribution and amplitude of lithospheric downwelling and examine how the instability develops adjacent to the corner of an initially rectangular region of thickened crust in a full 3D flow model. Observations of lithospheric thickness, Moho and surface topography, sediment distribution, and the observed spatial and temporal distribution of tectonics provide constraints on the numerical models that may lead to an improved understanding of the mechanisms that control the evolution of continental orogens.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2005
- Bibcode:
- 2005AGUSM.T51A..03G
- Keywords:
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- 1234 Regional and global gravity anomalies and Earth structure;
- 3210 Modeling;
- 8102 Continental contractional orogenic belts;
- 8109 Continental tectonics: extensional (0905);
- 8120 Dynamics of lithosphere and mantle: general