The formation of the intra-Carpathian basins as determined from subsidence data

The Carpathian arc is the result of continental collision during subduction of the European plate beneath a Pannonian continental block. In the Early/Middle Miocene, during and after the last stages of thrusting in the Outer Carpathians, several "back-arc" basins started to form within the Carpathian loop. These basins are of two types: (1) those lying in the peripheral regions of the intra-Carpathian lowlands (Vienna, West Danube, Transcarpathian and Transylvanian), and (2) those lying in the central intra-Carpathian region (East Danube, Little Hungarian and Great Hungarian (Pannonian)). Though both groups of basins have thin crust, the subsidence history and the present heat flow are different. The peripheral basins exhibit a rapid initial subsidence followed by a much slower general increase in depth. Their heat flow is close to the average for continental areas. In contrast the central basins have no initial subsidence but do show a fast linear increase in depth which has continued until the present. The heat flow is nearly twice the average for continents. We believe that the basins are thermal in origin and are the direct result of the continental collision which formed the Carpathian arc. The peripheral basins appear to be the result of uniform stretching of the lithosphere by about a factor of two. The rapid initial subsidence is an immediate isostatic adjustment to the stretching, the slower linear subsidence is due to conductive cooling of the thinned lithosphere. In the central basins, uniform stretching by about a factor of 3 could explain the thermal subsidence and the high heat flow. Unfortunately such a simple explanation is not supported by either the geology or the absence of a clearly defined initial subsidence. Alternative explanation involve crustal stretching with additional subcrustal thinning or, alternatively, attenuation of the whole subcrustal lithosphere and part of the crust by melting and erosion. Both explanations create a very thin lithosphere, reduce the initial subsidence to a minimum but still give a rapid thermal subsidence and high heat flow. The subsidence history gives quantitative information concerning the evolution of the inter-Carpathian basins. In other areas, it may place equally important constraints on the development of intercontinental basins and continental shelves.