Coalification and thermal histories of Tertiary basins in relation to late Alpidic evolution of the Eastern Alps

The thermal histories of Tertiary basins situated around and within the Eastern Alps are examined using coalification data. Waples' method is used to estimate paleogeothermal conditions. The data suggest that the basins' thermal histories are intimately related to late Alpidic geodynamics of the Eastern Alps. Basins situated near the thrust front (Eastern Alpine foredeep, Vienna basin) are characterized by 'hypothermal' histories and low coalification gradients. This is a consequence of relatively thick crust, high paleosedimentation rates in the Alpine foredeep, and Oligocene to Early Miocene stacking of cool sediments along the southern margin of the Eastern Alpine foredeep. Extension in the Vienna basin region is restricted mainly to shallow crustal levels and did not change the thermal pattern beneath the Alpine nappes. Major 'hyperthermal' events of Oligocene age and local coalification maxima in the central Slovenian basin date from magmatic activity along the Periadriatic lineament, caused by Oligocene subduction. In Miocene times subduction migrated eastward and magmatic activity shifted to the northern Slovenian and Styrian basins, resulting in a strong 'hyperthermal' phase of Ottnangian to Lower Badenian age in these basins. Rapid uplift of the Tauern window in the central part of the Eastern Alps, due to buoyancy, is related to E-W directed crustal stretching and resulted in raised heat flow in Miocene times in the Tauern window region, and in relatively high rank in adjacent Tertiary basins (Wagrain, Tamsweg). Present geothermal patterns are controlled primarily by raised heat flow along the south-eastern margin of the Alps, a consequence of thinned crust beneath the Pannonian basin.