20 Sep 2022
20 Sep 2022
Status: this preprint is open for discussion.

Rift thermal inheritance in the SW Alps (France): insights from RSCM thermometry and 1D thermal numerical modelling

Naïm Célini1,2,3, Frédéric Mouthereau2, Abdeltif Lahfid3, Claude Gout1, and Jean-Paul Callot1 Naïm Célini et al.
  • 1Université de Pau et des Pays de l’Adour, E2S UPPA, CNRS, TotalEnergies, LFCR, Pau, France
  • 2Géosciences Environnement Toulouse, Université de Toulouse Paul Sabatier, CNRS, IRD, Toulouse, France
  • 3Bureau des Recherches Géologiques et Minières, Orléans, France

Abstract. Conceptual models of orogenic accretionary prisms assume the increase in peak temperatures (Tmax) towards the internal domains as crustal rocks are accreted from the lower to the upper plate. Yet, the recognition of pre-orogenic heating events in mountain belts questions the magnitude of thermal overprint during nappe stacking. Using Raman Spectroscopy on Carbonaceous Material (RSCM) to calculate Tmax, we have investigated the thermal record of Lower Jurassic to Upper Cretaceous strata exposed along the Digne Nappe, at the front of the SW Alps. Our results highlight two groups of depth-dependent temperatures: (1) a regionally extensive constant Tmax up to 300–330 °C measured in the Jurassic succession and (2) regionally variable lower temperature (<150 °C) recorded either in the upper Mesozoic, the nappe stack or the syn-orogenic sequence. Modelling shows that the highest paleotemperatures were achieved during the Early Cretaceous (~130 Ma), during the Valaisan-Vocontian rifting, while the lowermost ones reflect syn-orogenic burial in the Alpine foreland basin. This study provides a striking new example where mid-crustal paleotemperatures measured in lower plate sediments now accreted at the thrust front are inherited. Estimated peak thermal gradient of 80–90 °C/km requires crustal thickness of ~15 km during the Early Cretaceous, hence placing new constraints for tectonic reconstruction of rift domains and geophysical interpretation of current crustal thickness in the SW Alps. These results call for the careful interpretation of paleothermal data when they are used to identify past collisional events. Where details of basin evolution are lacking high-temperature record may be misinterpreted as syn-orogenic, which can in turn lead to overestimating both orogenic thickening and horizontal displacement in mountain belts.

Naïm Célini et al.

Status: open (until 01 Nov 2022)

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Naïm Célini et al.


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Short summary
We investigate the peak temperature of sedimentary rocks of the SW Alps (France), using the Raman Spectroscopy on Carbonaceous Material. This method provides an estimate of the peak temperature achieved by organic-rich rocks. To determine the timing and the tectonic context at the origin of these temperatures we use 1D thermal modelling. We find that the high temperatures up to 300 °C were achieved during pre-collisional extensional events, not during tectonic burial in the Western Alps.