Impact of Salt Tectonics on Temperatures Distribution Revealed by RSCM Thermometry in the SW Alps (France)

Abstract

Evaporites have a strong impact on the structural and sedimentary evolution of sedimentary basins and fold-and-thrust belts. They also have a thermal conductivity that can be more important than other sedimentary rocks and are thus able to modify the thermal history of these sedimentary basins and fold-and-thrust belts. Even though this property is known and has been of interest for the oil and gas industry, no field examples have been studied trying to decipher how salt rock impacts temperature distribution in fold-and-thrust belts. In this paper, we use the Raman Spectroscopy on Carbonaceous Material (RSCM) to track the record of the peak thermal event around three salt structures from the southern sub-Alpine fold-and-thrust belt in SE France. These three salt structures are (1) the Astoin allochthonous salt sheet and the associated overturned megaflap, (2) the Rocher de Hongrie and (3) the Daluis diapir. Our results show that the resulting record of peak temperatures around the structures is different depending on the type of salt structure and its kinematic. The Astoin structure shows that salt tectonics during the Jurassic-Cretaceous has impacted the temperature distribution around the allochthonous salt sheet while at Daluis and the Rocher de Hongrie, the temperatures have overprinted an already existing salt-related structure. The impact of the salt structure on temperature distribution is always local but the interpretation of the RSCM temperatures may systematically be difficult without considering early salt tectonics in the structural evolution of the area.