Institute of Geophysics and Tectonics (IGT) PhD Projects
Geodynamics of the Carpathian-Pannonian System
Supervisors: Professor Greg Houseman
Since 2005 the University of Leeds, supported by NERC and in partnership with Institutes in Hungary, Austria, Serbia and Romania, has led a deep seismic investigation, firstly of the western Pannonian Basin and currently of the eastern Pannonian and South Carpathian Range. The object of this investigation has been to determine the seismic structure of the lithosphere and upper mantle of the Pannonian-Carpathian orogenic system. In conjunction with the seismic investigation we are also developing geodynamic models of the evolution of the Pannonian-Carpathian system using finite-element methods to simulate large-strain continuum deformation (Lorinczi and Houseman, 2009).
The Pannonian Basin was extended rapidly between about 17 and 12 Myr ago. Coincident with this extension, convergence in the surrounding Carpathian Mountain chain occurred, prompting models in which coupled extension and convergence are driven by gravitational instability of the lithosphere (Houseman and Gemmer, 2007), or by roll-back of an oceanic slab subducting beneath the NE Carpthians (Horvath, 1993). Whatever the mechanism, the upper mantle beneath this region is very anomalous: seismic waves propagate unusually slowly in the upper several hundred km, and unusually quickly below the olivine to spinel phase change at 410 km depth (Wortel and Spakman, 2000). Our first major seismic project - the Carpathian Basins Project (2005-2007) has revealed a fast vertical structure in the mantle beneath the Pannonian Basin and slow material beneath the Western Carpathians (tomographic analysis is presently being finalised by PhD student Ben Dando). We also found that the 660 km spinel to perovskite phase boundary is depressed beneath most of the Carpathian basin, by as much as 40 km (Hetenyi et al., 2009), as if it is supporting a layer of denser material derived from the extended and thinned lithosphere above.
Our team is currently collecting more seismic data, with 57 temporary stations deployed over a broad region of eastern Hungary, western Romania and SE Serbia. This array covers most of the eastern Pannonian Basin and the South Carpathian Range, and it will greatly increase the extent and resolution of our images of the upper mantle beneath the Pannonian-Carpathian region. Within this project there is scope for one or more PhD projects in which the student will analyse seismic data in order to better constrain the deep structure of the upper mantle and/or work to further develop the geodynamical models that describe the processes that occurred when the Pannonian Basin formed and the upper mantle beneath this region was overturned. One high-priority project would involve the analysis of converted waves at the spinel-to-perovskite phase transition (nominally at 660 km depth), and development of a geodynamical model using finite element methods which explains quantitatively why, where, and by how much this boundary is depressed. The student will obtain experience in analysis of array seismic data for regional scale problems, and in the development of programming techniques needed for the simulation of continuum mechanics problems using parallel computer systems.
Enquiries to: Prof G. A. Houseman - G.Houseman(at)see.leeds.ac.uk
References:
Hetenyi, G; Stuart, GW; Houseman, GA; Horvath, F; Hegedus, E; Bruckl, E (2009) Anomalously deep mantle transition zone below Central Europe: Evidence of lithospheric instability, GEOPHYS RES LETT, 36, . doi:10.1029/2009GL040171
Horváth, F. (1993), Towards a mechanical model for the formation of the Pannonian Basin, in Cloetingh, S; Sassi, W; Horváth, F., eds., The origin of sedimentary basins; inferences from quantitative modelling and basin analysis: TECTONOPHYSICS, 226, p. 333-357.
Houseman, GA; Gemmer, L (2007) Intra-orogenic extension driven by gravitational instability: Carpathian-Pannonian orogeny, GEOLOGY, 35(12), pp1135-1138. doi:10.1130/G23993A.1
Lorinczi, P; Houseman, GA (2009) Lithospheric gravitational instability beneath the Southeast Carpathians, TECTONOPHYSICS, 474(1-2), pp322-336. doi:10.1016/j.tecto.2008.05.024
Wortel, M.J.R. and Spakman, W., (2000), Subduction and slab detachment in the Mediterranean-Carpathian Region: SCIENCE, 290, p. 1910-1917.