HR: 08:00h
AN: U51B-01 INVITED     [Abstracts]
TI: Lithospheric Extension Within a Continental Orogen: The Pannonian Basin
AU: * Houseman, G A
EM: greg@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Woodhouse Lane, Leeds, LS82PF United Kingdom
AU: Gemmer, L
EM: lykke@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Woodhouse Lane, Leeds, LS82PF United Kingdom
AB: The Alpine-Carpathian-Pannonian system of central and eastern Europe is the classic example of a continental extensional basin surrounded by convergent mountain belts. It developed rapidly in the Miocene and remains active today. The temporal and spatial distribution of tectonic deformation in orogenic regions that exhibit contemporaneous extension and convergence in adjacent regions is complex and remains poorly understood. This complexity may be attributed to the interplay between internal buoyancy forces and regional stress fields. Although roll-back of subducted slabs, and mantle plumes, have been invoked as driving mechanisms, we propose that gravitational instability of the continental lithosphere was probably the dominant causal mechanism for the formation of this system. In general, the mantle lithosphere beneath the continents is colder, and thereby denser, than the underlying asthenosphere. Instability may develop, triggered by convergence, causing the mantle lithosphere to sink into the underlying asthenosphere. We use dynamically self-consistent 3D numerical models of lithospheric and crustal deformation to investigate the instabilities that may develop when the initially stratified system is perturbed by tectonic or thermal disturbances of different type, shape, or wavelength. A region of crust initially thickened by localized convergence will tend to spread under its own weight, and possibly trigger the development of instability of the dense mantle-lithosphere layer. Lithospheric thinning then develops simultaneously with convergent deformation and lithospheric downwelling in the adjacent areas. We investigate how the distribution and amplitude of lithospheric downwelling depends on the relative viscosities and densities of the two layers, and show that the instability develops more slowly at the corner of an initially rectangular region of thickened crust. These mechanisms may explain some of the lateral variations in timing and amplitude of deformation observed in the Alpine-Carpathian-Pannonian system and other continental convergent orogens. Localised heating and extension of the mantle lithosphere beneath the continents is therefore much more readily induced by gravitational instability of that layer than by the thermal effect of a deep mantle plume.
DE: 8107 Continental neotectonics (8002)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8122 Dynamics: gravity and tectonics
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8164 Stresses: crust and lithosphere
SC: Union [U]
MN: Fall Meeting 2005