Thermal and tectonic evolution of the southern Alps (northern Italy) rifting: Coupled organic matter maturity analysis and thermokinematic modeling

The southern Alps were characterized by strong variations, both in space and time, of heat flow during Mesozoic rifting. The regional thermal history was reconstructed using organic matter (OM) maturity data from outcropping sediments. One-dimensional (1-D) thermal modeling performed on selected successions suggests that OM maturity was mainly controlled by high geothermal gradients (heat flow peaks of 85 to 105 mW/m(2) in the Middle Jurassic) and differential burial during Norian-Early Jurassic extensional phases. The results of 1-D modeling show an eastward increase of heat flow peak values. These results were compared with those obtained with two-dimensional (2-D) thermokinematic models. The models show a time shift (ca. 10 Ma) in the heat-flow peak (Aalenian-Bajocian for 2-D and Bajocian for 1-D modeling). However, the Bajocian age was a priori imposed on 1-D models. Available geochemical data could be fitted assuming Aalenian-Bajocian peak ages. Consequently, this misfit is not alarming. The eastward increase in heat-flow peak values is tentatively explained with an eastward increase of radiogenic heat production in the crust instead of with differential stretching. The comparison of paleothermal data and numerical modeling was done to gain knowledge on the potentials and limitations of numerical modeling in frontier areas. Although some differences do exist in the results of geochemical and thermokinematic models, we can conclude that if a reasonable knowledge of the thermal parameters of both covers and basement is available, thermokinematic modeling can provide useful first-order estimates in frontier areas of heat flow and temperature evolution through time.