Unraveling the eroded units of mountain belts using RSCM thermometry and cross-section balancing: example of the southwestern French Alps

Abstract

Reconstruction of eroded mountain belt structures is crucial to produce valid precontractional palinspastic restorations and quantify the amount of shortening. In this study, we combine Raman Spectroscopy of Carbonaceous Material (RSCM) thermometry and cross-section balancing technique to propose a reconstruction of the thermal and deformational evolution of the Subalpine Digne Nappe in the southwestern French Alps. We sampled Mesozoic to Cenozoic sedimentary strata for RSCM thermometry analyses along the ~4-km-thick Digne Nappe to calculate maximum temperatures (T RSCM ). T RSCM values range from 243±10°C to 349±13°C in the upper Triassic-upper Cretaceous strata and from 255±19°C to 328±8°C in the overlying upper Eocene-lower Oligocene strata. T RSCM values show a gradual increase with depth and towards the inner part of the orogen. These results are consistent with a ~28±4°C/km modeled thermal gradient in the ~4-km-thick Digne Nappe 2 and suggest post Oligocene burial of the Digne Nappe under sedimentary/tectonic units that have been removed by erosion. Palinspastic restoration of a NE-trending and 65-km-long cross-section (Digne-Barcelonnette transect) constrained by thermal data supports the interpretation that the Digne Nappe involved a ~3-km-thick middle/upper Eocene-Oligocene to lower Miocene foreland basin tectonically overlain by the 3-to 11-km-thick Embrunais-Ubaye flysch nappes. The front of the Embrunais-Ubaye nappes was located ~40 km beyond its present erosional front. The amount of southwestward shortening in the Subalpine thrust wedge derived from palinspastic restoration is about 35 km (35%) over the past ~16 million years. Removal of a substantial volume of the southwestern Alpine orogen may have significantly influenced the dynamics of the Subalpine thrust wedge and Valensole foreland basin since the Middle Miocene.

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

“…Fluid inclusions were studied to apprehend the maximum burial reached in the Vocontian Domain (Perthuisot and Guilhaumou, 1983;Guilhaumou et al, 1996). A few studies were focused on the estimation of eroded syn-orogenic deposits or internal units that have overthrusted the external units during orogeny using thermochronology on clastic deposits (Labaume et al, 2008;Jourdan et al, 2013;Schwartz et al, 2017), vitrinite reflectance (Deville and Sassi, 2006) or the RSCM approach (Bellanger et al, 2015;Boutoux et al, 2016;Girault et al, 2020;Balansa et al, 2023). A recent study using the RSCM approach and basin modelling evidenced a thermal inheritance of the rifting phases highlighting that the peak temperatures have not been overprinted during the orogeny (Célini et al, 2023) such as proposed in the internal units of the Maritime Alps (Decarlis et al, 2017).…”