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Abstract

We reconstructed the thermal history, and therefore the evolution of heat flow in the southern Alps region (northern Italy), using organic matter (OM) maturity data obtained from samples of sedimentary units outcropping along the entire mountain chain. Regional OM maturity patterns are largely controlled by a high geothermal gradient and differential burial during the Norian–Liassic extensional phase. Good results for thermal history calibrations from several locations were obtained using a large database of measured OM maturity, consisting of different maturity parameters, often all in agreement, for a wide range of lithostratigraphic sequences.

One-dimensional thermal modeling was applied to selected successions that were not overprinted by alpine evolution. Resulting heat-flow values were high and relatively uniform (85 to 105 mW/m2) throughout the southern Alps during the Lias–Early Dogger, and they progressively decreased after the Bajocian–Bathonian to values similar to the present-day heat flow (50 to 55 mW/m2) by the end of the Cretaceous. This heat-flow reconstruction is consistent with the known tectonic evolution of Mesozoic extension in the southern Alps, characterized by a rifting stage lasting to the Lias, followed by a drifting stage beginning in the Middle Jurassic.

Elevated heat flow in the southern Alps has important implications for hydrocarbon exploration. Upper Triassic source rocks in basinal successions attained high maturity during the Jurassic, and this is even more likely for the deeper Middle Triassic source rocks.

Improved definition of the heat-flow peak in the Jurassic helps to define the hydrocarbon charge risk associated with leads and prospects in the Po Plain subsurface, where traps formed in the Cenozoic. In areas characterized by little Rhaetian–Liassic burial, the source rocks retained their original petroleum potential prior to strong Neogene–Quaternary burial and heating.

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