HR: 09:15h
AN: T31E-06    [Abstracts]
TI: Lithospheric Gravitational Instability Beneath the South-East Carpathians
AU: * Lorinczi, P
EM: p.lorinczi@see.leeds.ac.uk
AF: School of Earth and Environment University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Houseman, G
EM: g.houseman@see.leeds.ac.uk
AF: School of Earth and Environment University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AB: The Carpathians are a major mountain system of the Central and Eastern Europe, which in the South-east surround the Transylvanian basin. Located on the oroclinal bend of the Carpathian mountains, the Vrancea region is characterised by a localised (~ 30 km x 80 km in the horizontal plane) zone of seismic activity to depths of 200 km. This phenomenon has been attributed to subduction of oceanic lithosphere. However, there is no obvious zone of subduction associated with the Vrancea deep earthquakes. An alternative explanation to this deep seismicity is the downwelling of the continental lithosphere in the form of a Rayleigh Taylor instability. The fault plane solutions, for a time interval of 40 years, indicate maximum vertical extension rates on the order of 14% per Myr in the depth range 50-100 km, decreasing by about an order of magnitude in the depth range 100- 150 km. Such rapid rates of deformation clearly represent a recent development, that could not have persisted for a period of time much greater than 5 Myr, and cannot be clearly attributed to recent subduction. Three dimensional finite deformation models of the gravitational instability of the continental lithosphere, based on the finite element method, demonstrate that the Rayleigh Taylor mechanism can explain the present distribution of deformation within the downwelling lithosphere, both in terms of distribution of seismicity and amplitude of strain rates. The spatial width of the high stress zone that corresponds to the seismically active zone is realistically represented when we assume that viscosity decreases by an order of magnitude across the lithosphere. The mantle downwelling is balanced by lithospheric thinning in an adjacent area which would correspond to the Transylvanian basin. This type of planform is inherently three dimensional and is triggered in these experiments by a harmonic perturbation in the form of a first order Bessel function (with m=1 asymmetry). In these models mantle downwelling is associated with crustal thickening but the lithospheric thinning beneath the adjacent basin is associated with only minor crustal thinning.
DE: 8108 Continental tectonics: compressional
DE: 8109 Continental tectonics: extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8123 Dynamics: seismotectonics
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting