Syn- and post-collisional heat flow in the Cenozoic Eastern Alps

The heat flow evolution of a continental collisional zone is exemplified by the Eastern Alps. Heat flow maps for the syn-collision (Oligocene), syn-ex trusion (Early/Middle Miocene), and post-extrusion (Late Miocene, Recent) s tages are presented, and are discussed in relation to the orogenic evolutio n. Continental collision during Paleogene time was characterized by extreme ly low heat flow (<40 mW/m(2)) along the orogenetic front, and very high he at flow (>150 mW/M-2) a few hundred kilometers south of it. The former was a result of crustal thickening and of thermal blanketing due to rapid sedim entation and nappe stacking. The latter was caused by slab break-off and ma gmatic activity. The Early/Middle Miocene syn-extrusion stage was character ized by rapid exhumation of metamorphic core complexes (Tauern and Rechnitz Windows), and by magmatic activity (Styrian Basin). Both mechanisms caused extremely high heat flow (>200 mW/m(2)). In contrast, the orogenetic front remained cold. Thereafter, magmatic activity ended and uplift rates decrea sed. Thus, Late Miocene heat flow is characterized by low to moderately hig h values. Heat flow values >75 mW/m(2) were restricted to the transition zo ne of the Pannonian Basin characterized by thinned crust, and to the Tauern Window area. Recent temperature data indicate a subtle post-Miocene increa se in heat flow.