HR: 0800h
AN: T31A-1273    [Abstracts]
TI: Lithospheric structure of the West-Pannonian Basin, based on CELEBRATION 2000 and ALP2002 3D seismic data and mantle xenolith lithology: an integrated approach
AU: * Kovacs, A C
EM: kacs@elgi.hu
AF: ELGI, Columbus 17-23, Budapest, 1145 Hungary
AU: Falus, G
EM: falus@elgi.hu
AF: ELGI, Columbus 17-23, Budapest, 1145 Hungary
AU: Takacs, E
EM: takacs@elgi.hu
AF: ELGI, Columbus 17-23, Budapest, 1145 Hungary
AU: Fancsik, T
EM: fancsik@elgi.hu
AF: ELGI, Columbus 17-23, Budapest, 1145 Hungary
AU: Hegedus, E
EM: hegedus@elgi.hu
AF: ELGI, Columbus 17-23, Budapest, 1145 Hungary
AU: Csabafi, R
EM: csabafi@elgi.hu
AF: ELGI, Columbus 17-23, Budapest, 1145 Hungary
AB: The nature of the lower crust and upper mantle can only be revealed using geophysical methods or studying rocks which derive from this deep part of the lithosphere. In our work we tried to combine these methods in anticipation of more realistic view of the deep lithosphere in the Pannonian Basin. The seismic survey was designed to obtain not only in-line recordings along five profiles, but also fan recordings of the off-line shots. The station spacing was changing between 1,5 and 5 km, the average charge of the seismic shots were 500 kg TNT. The use of 409 single channel (Texan, PRS) recorders and 20 seismic sources provided a sufficient 3D ray coverage over an 250km * 240km area, and allowed for construction of a 3D model of the crustal structure. The seismic sections show clear first arrivals up to a distance of 180-200 km. For tomographic modeling 5700 picks of first arrivals were used. The P-wave velocity model was defined at equidistant nodes of the 3D rectangular grid. The distance between nodes was 0.5 km. The initial model used was established by apriori velocity data of the pre-Tertiary sediments. For the tomographic inversion of the areal data we used FAST package developed by C. Zelt (1998). The crustal velocities in the West-Pannonian Basin are relatively low, around 6.1-6.3 km/s in the upper crust, with thin lower crust characterized by velocities around 6.5 km/s, suggesting crustal extension. The Moho depth varies 30-32 km in the Transdanubian Central Range area, 27 km in the Mid-Hungarian Zone, with upper mantle velocities 7.8-8.0 km/s. Peridotite xenoliths hosted in young alkaline basalts from the West-Pannonian Basin (Little Hungarian Plain and Bakony-Balaton Highland) have been also extensively studied regarding their deformation microstructures and geochemical characteristics. Our results suggest that the formation of the Pannonian Basin was associated with deformation, induced by considerable (45-50 km) lithospheric thinning, and geochemical modification of the lithospheric mantle. Xenoliths from the shallow mantle (30-40 km) of the western Pannonian Basin display depleted major element and enriched incompatible trace element compositions indicative of partial melting and subsequent refertilization. Deformation microstructures designate multiple stage complex deformation, characterized by unusual olivine fabrics. Conversely, xenoliths from the deep lithosphere (>40 km) show fertile major element and depleted incompatible trace element contents similar to that of the asthenosphere and exhibit evidence for simple, single stage deformation related to asthenospheric flow. We suggest that the mantle portion represented by these xenoliths was only attached to the bottom of the lithosphere after cooling and the cessation of deformation. Our complex study demonstrates that considerable (40-50 km) lithosphere thinning took place during the formation of the Pannonian Basin, which manifested both in the lower crust and upper mantle associated with geochemical modification of the lower lithosphere. This integrated approach is a powerful tool in reconstructing the evolution of the Pannonian Basin.
DE: 8180 Tomography
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting