New Structural and RSCM Thermometric Data from the Variscan Orogen of Morocco: Insight into the Extension-To-Compression Transition

The Western Moroccan Meseta exposes in the Zaian region a pre-Visean, Eo-Variscan belt of inclined to recumbent folds detached from their Precambrian basement and embedded in the Variscan Orogen. Using the Raman Spectroscopy of Carbonaceous Material (RSCM) method, we obtained the first quantitative thermometric characterization of the Cambro-Ordovician and unconformable Upper Visean rocks in the area. The pre-Visean fold belt developed in relatively high-T conditions (mean value 323 ± 23 °C) compared to the juxtaposed Variscan folds that formed at lower T (209 ± 37 °C). The high geotherm of the Paleozoic series during folding is likely to be inherited from the Late Devonian extensional setting, but the fold belt emerged through compression, probably during the Devonian-Tournaisian transition.