Péter Szafián

Lithospheric structure of the Pannonian basin derived from seismic, gravity and geothermal data

Abstract The structure of the Pannonian basin is the result of distinct modes of Mid-Late Miocene extension exerting a profound effect on the lithospheric configuration, which continues even today. As the first manifestation of extensional collapse, large magnitude, metamorphic core complex style extension took place at the beginning of the Mid-Miocene in certain parts of the basin. Extrapolation of the present-day high heat flow in the basin, corrected for the blanketing effect of the basin fill, indicates a hot and thin lithosphere at the onset of extension. This initial condition, combined with the relatively thick crust inherited from earlier Alpine compressional episodes, appears to be responsible for the core complex type extension at the beginning of the syn-rift period. This type of extension is well documented in the northwestern Pannonian basin. Newly obtained deep reflection seismic and fission-track data integrated with well data from the southeastern part of the basin suggests that it developed in a similar fashion. Shortly after the initial period, the style of syn-rift extension changed to a wide-rift style, covering an area of much larger geographic extent. The associated normal faults revealed by industry reflection seismic data tend to dominate within the upper crust, obscuring pre-existing structures. However, several deep seismic profiles, constrained by gravity and geothermal modeling, image the entire lithosphere beneath the basin. It is the Mid-Miocene synrift extension which is still reflected in the structure of the Pannonian lithosphere, on the scale of the whole basin system. The gradually diminishing extension during the Late Miocene/Pliocene could not advance to the localization of extension into narrow rift zones in the Pannonian region, except some deep subbasins such as the Makó/Békés and Danube basins. These basins are underlain coincidently by anomalously thin crust (22–25 km) and lithosphere (45–60 km). Significant departures (up to 130 mW m−2) from the average present-day surface heat flow (c. 90 mW m−2) and intensive Pliocene alkaline magmatism are also regarded as evidence for the initiation of two newly defined narrow rift zones (Tisza and Duna) in the Pannonian basin system. However, both of these narrow rifts failed since the final docking of the Eastern Carpathians onto the European foreland excluded any further extension of the back-arc region.

Asthenospheric structure beneath a Neogene basin in southeast Hungary

Abstract Beneath one of the subbasins of the Pannonian basin formed between the Alps, Carpathians and Dinarides — the Bekes basin in southeast Hungary — a typical structure of the lithosphere and an upwelling of the asthenosphere can be inferred from seismic reflection, geothermal, geomagnetic, gravity and magnetotelluric investigations. In the Bekes basin the thickness of Neogene sediments reaches 6–7 km, i.e. the basement of the Neogene basin sinks 3–4 km over the basin area. In the reflection section of the Pannonian Geotraverse that ends in the Bekes basin the crust-mantle boundary rises by 5–6 km up to a depth of 22 km. In the course of performing and processing seismic reflection measurements particular care was given to the preservation of low-frequency (2–10 Hz) information. This explains that data were successfully received even from the upper mantle. Amplitude distribution of reflection arrivals and the dipping of reflecting surfaces permit to infer an uplift by 15–20 km in the lithosphere-asthenosphere boundary which thus is assumed to be at a depth of 40–45 km beneath the Bekes basin. In geothermal investigations the model was established with seismic results being accounted for, assuming an upwelling in the lithosphere-asthenosphere boundary. The superficial heat flow density corrected for the cooling effect of sediments was in good agreement with the values of model calculations. The latest magnetotelluric results support the upwelling position of the lithosphere-asthenosphere boundary. The geomagnetic anomaly determined over the area of the Bekes basin can be explained by the uplifted position of the lower crust. The gravity anomaly can be attributed to the combined effect of this and the upwelling in the crust-mantle boundary. It is hoped that the integrated interpretation of results obtained by various geophysical methods confirms the assumption that said methods permit to investigate the structure of the whole lithosphere and thus the disclosed results may contribute to the completion and precision of basin models studied so far.

Gravity constraints on the crustal structure and slab evolution along a transcarpathian transect

Abstract A new, unified Bouguer anomaly map of the Carpathian arc and the Pannonian basin has been compiled from previously prepared and recently published gravity maps. In order to constrain the crustal structure and the tectonic evolution of the area, a two-dimensional gravity model is presented along a Western Carpathians-Pannonian basin-Southern Carpathians transect. The model is based on deep seismic lines, where available, and on detailed geological sections. The results confirm that the extensional crustal structure of the Pannonian basin revealed by deep seismic surveys agrees with the gravity data. Furthermore, they suggest that the Western and Southern Carpathians area at different stages of their evolution: the subducted oceanic slab under the Western Carpathians has already been assimilated to the asthenosphere, while a crustal slab is still present under the Southern Carpathians. These findings are compatible with the observation that the last major phase of crustal shortening terminated at the early Middle Miocene in the Western Carpathians, but continued throughout the Pliocene in the Southern Carpathians.

Slope-toe Turbidite Systems Related to Aggradational - Progradational Sequences: Potential Stratigraphic Traps in the Makó Trough, Pannonian Basin, Hungary

Though the Mako Trough is best known as the location of major unconventional gas accumulations, the thick Neogene to Quaternary sedimentary successions may contain conventional HC resources as well. Structurally controlled traps are widespread on the neighbouring basement highs and not likely to occur in the basin interior. However, stratigraphic traps, untested so far, were identified in relation to the basin-filling progradational slope system. The style and pace of slope advancing are the key to understand sand delivery to and formation of potential reservoirs in the deep parts of the basin.