Thermomechanical consequences of Cretaceous continent-continent collision in the eastern Alps (Austria): Insights from two-dimensional modeling

We use two-dimensional numerical modeling techniques to investigate the the rmomechanical consequences of closure of the Meliata-Hallstatt ocean and co nsequent Cretaceous continent-continent collision in the eastern Alps (Aust ria). In the modeling a lower plate position of the Austro-Alpine (AA) cont inental block is adopted during collision with the Upper Juvavic-Silice blo ck. The thermal structure of the lithosphere was calculated for major AA te ctonic units (Upper, Middle, and Lower Austro-Alpine) by integration of the transient heat flow equation along an approximately NW-SE cross section ea st of the Tauern Window. Indications of the rheological evolution of the AA were determined by calculating strength profiles at key stages of the Cret aceous orogeny, making use of the thermal modeling predictions combined wit h rock mechanics data. Cooling in the upper plate and lower greenschist fac ies metamorphism within footwall parts of the lower Upper Austro-Alpine (UA ) plate, related to SE directed underthrusting of the UA beneath the Upper Juvavic-Silice block at circa 100 Ma, were predicted by the numerical model . The observed pressure-temperature path for deeply buried Middle Austro-Al pine (MA) upper crustal units and their subsequent isothermal exhumation ar e best reproduced assuming a pressure peak at 95 Ma and exhumation recites ranging between 4 and 7.5 mm yr(-1). From the modeling results, we deduce t hat the temperature evolution during eclogite exhumation is primarily depen dent on rates of tectonic movements and largely independent of the mode of exhumation (thrusting versus erosion). Furthermore, very rapid postmetamorp hic exhumation of southern Lower Austro-Alpine (LA) units is predicted in o rder to account for subsequent cooling. This is constrained by As-40/Ar-39 data. The cooling paths of MA and LA rocks appear to be primarily controlle d by their near-surface positions at the end of the Cretaceous rather than by other processes such as concurrent underthrusting. Upward advection of h eat by rapid exhumation induced thermal weakening of the thickened crust. T he inferred weakness of the central parts of the orogenic system may play a n important role during detachment-related tectonic unroofing, orogenic col lapse, and concomitant basin formation (central Alpine Gosau basins).