QUANTITATIVE MODELLING OF SUBSIDENCE, EROSION AND THERMAL HISTORY OF THE DOLOMITES, NORTHERN ITALY

The Dolomites in Northern Italy, as part of the Southern Alps, are characterized by a complex poly-phase geological evolution. The sedimentary succession of the Dolomites, mainly Permian and Mesozoic in age, underwent several deformation phases followed by a final compression and inversion during the Meso- and Neo-alpine orogeny. This study quantifies the subsidence, erosional and thermal history of the Dolomites by combining high resolution litho-stratigraphy, organic matter maturity measurements and apatite fission track analyses (AFTA) with basin modeling. The multi-scale and multi-disciplinary based quantification of the thermal history is a key to improve the understanding of the geological processes in the Southern Alps.

This study incorporates newly obtained vitrinite reflectance and geochemical maturity measurements from outcrop samples from more than 100 locations along the TransAlp seismic traverse. The results have been plotted into a set of eight coalification maps and establish a new spatial and temporal insight of thermal maturity of organic matter. The further analysis of this new data reveals an increasing thermal maturity with increasing stratigraphic age within the Permo-Mesozoic strata along the investigated profiles. Vitrinite reflectance ranges from about 0.9 % VR_r for Permian strata to 0.5 % VR_r for Cretaceous strata. The thermal maturity (vitrinite reflectance) gradient indicates also a deeper burial than preserved in the sedimentary record. This strongly implies that the maximum temperature exposure of the Permian and Mesozoic sediments occurred prior to the deformation during the Meso- and Neoalpine orogeny. The results of the apatite fission track analyses and modelling from the sampled Permian Val-Gardena, Buchenstein- and Wengen-Formation support this conclusion and date the cooling into the Eocene (ca. 40 Ma).

Finally, we used calibrated one-dimensional (1D) basin models based on reconstructed pseudo-wells to quantify the paleo heat flow history as well as the erosional amount for the central Dolomites. The erosional amount of the Cretaceous to Tertiary overburden with the best fit (of VR_r and AFTA data) was determined to range between 1400 and 2300 m with an optimum around 1800 m.