Thermal effects of exhumation of a metamorphic core complex on hanging wall syn-rift sediments: an example from the Rechnitz window, eastern Alps

The removal of overburden by tectonic processes displaces the rock masses a nd their temperature with respect to the surface. Consequently high cooling rates and increased heat flow have been reported from rapidly exhuming ter rains. Previous studies were mainly focused on the greenschist- and amphibo lite-facies tectono-thermal evolution of the footwall. A two-dimensional nu merical thermal model presented in this study concentrates on the thermal h istory of the hanging wall and the footwall blocks and evaluates the variat ion of the near-surface heat flow above an evolving metamorphic core comple x. Based on structural, thermobarometric and geochronological constraints f rom the Rechnitz core complex of the Eastern Alps the modelling suggests th at rapid movement along the extensional fault took place between 22 and 17 Ma. During this period the heat how reached values of 140-150 mW/m(2) in th e hanging wall in a 10-15-km-wide zone parallel to the fault trace. The inc reased heat flow caused the high coal rank in the Miocene syn-rift sediment s deposited on the hanging wall, Apatite fission track geochronology of the thermally overprinted sedimentary deposits gives the time at which the bot tom of the syn-rift sediment pile passed through 110 degrees C (13.6 +/- 0. 9 Ma). The vitrinite reflectance data (R-r: 0.67-1.04%) suggest significant burial of the margin of the hanging wall at the time of core complex forma tion. Considering the coal rank data and the thermal conductivity of the se dimentary deposits by modelling of the organic maturation we calculate syn- rift (Early-Middle Miocene) burial of the hanging wall margin of the Rechni tz core complex to be 1100-1600 m. This value shows the importance of the p ost-Middle Miocene erosion of the region, which was related to the inversio n of the Pannonian basin. (C) 1998 Elsevier Science B.V. All rights reserve d.