Analysis of sedimentation and thermal data indicates that, for most parts of the Pannonian basin, observed heat flow, thermal gradients, rates of thermal subsidence and vitrinite reflectance are about twice those predicted by assuming a uniform extension model for basin formation in late Miocene time. A modified extension model, whereby large amounts of heat are added to the uppermost mantle during extension (roughly equivalent to replacing the entire sub‐crustal lithosphere by asthenosphere), produced results in good agreement with observation and could also account for periods of uplift observed during extension. Crustal extension beneath most parts of the basin is estimated to have been about 80% to 170% (β = 1.8 to 2.7), although in the deepest parts of the basin (deeper than 4 km) crustal extension could have been much greater. Analysis of extension within the Danube and Zala basins indicates that the late Miocene extension in these basins involved the entire lithosphere, but subsidence and heat flow data are not well enough constrained to determine if extra heating is required during extension. On the basis of tectonic and structural data, the Vienna basin has been interpreted as the result of thin‐skinned extensional tectonics above a shallow detachment surface within the upper crust (Royden et al. [this issue]). Analysis of thermal and subsidence data from the northern Vienna basin suggests that little or no heating occurred during basin extension. These data are consistent with a thin‐skinned extensional origin for the Vienna basin, and are in better agreement with this interpretation than with the assumption of a uniformly extended lithosphere beneath the basin. This study emphasizes the need for good thermal, subsidence and structural data in making reconstructions of extensional and thermal histories of sedimentary basins. When such data are available, it is found that a simple uniform extension model does not explain very well the evolution of some sedimentary basins, such as the Vienna and Pannonian basins. In the first instance, the basin is thought to be the result of upper crustal extension only, due to its special tectonic setting, in the second instance, the extra heating during extension is due to some unknown processes in the lower lithosphere that may be a general feature of lithospheric extension. Thus, lithospheric extension (and associated heating) may be distributed in a variety of ways; not all extensional sedimentary basins form in the same way. Application of a uniform subsidence model to basins for which good thermal, subsidence and structural data are not available (or not properly analysed) can lead to reconstructions of thermal histories in error by a factor of 2 or more.
ASJC Scopus subject areas
- Geochemistry and Petrology