Interpretation of vintage 2D seismic reflection data along the Austrian-Hungarian border: Subsurface expression of the Rechnitz metamorphic core complex

Abstract

In the border zone between Austria and Hungary, the Miocene extension of the Pannonian Basin was characterized by extreme, large-magnitude upper crustal extension accommodated along low-angle detachment faults. Although some of these prominent normal faults have already been described using 2D seismic data sets and well data on the Hungarian side, we offer the first systematic interpretation using the Austrian and Hungarian vintage seismic data sets acquired in the 1970s and 1980s. The refinement of the previously proposed metamorphic core complex (MCC) style, east-northeast–west-southwest-trending very high-strain extension provides a modern understanding of back-arc extension in this part of the Pannonian Basin system as the result of the collapse of the Alpine orogen. Although previous interpretations could not achieve the subsurface correlation of major structural elements across the border, we did systematically map these for the first time. Numerous exploration wells, drilled on both sides of the border, were integrated with reflection seismic data to differentiate between the lower versus upper plates of the major low-angle detachment faults, including the largest one responsible for the formation of the Rechnitz MCC. Based on our new interpretation, the regionally mapped Rechnitz detachment fault has an unexpectedly large subsurface extent, on the order of 1000 km2. Moreover, the unusually large number of industry 2D seismic profiles (approximately 50) used to map this and other prominent faults, in the Austrian and Hungarian sides, makes the Rechnitz MCC possibly the best constrained one in the world in terms of subsurface definition by reflection seismic data.