Thermal variation across collisional orogens: Insights from the hinterland–foreland transition zone of the Sardinian Variscan belt

Unravelling the architecture and evolution of orogenic wedges are often hampered by the presence of strongly deformed large-scale nappes made by homogeneous metasedimentary rocks lacking diagnostic metamorphic phases. Involving nappes or tectonic units which occupy most of the chain, reconstructing the thermal architecture of the hinterland–foreland transition zone of collisional belts represents a key point to comprehend the orogenic wedge tectonics. This work provides new thermal data from Raman Spectroscopy on Carbonaceous Material (RSCM) carried out in the low-grade metamorphic rocks of the hinterland–foreland transition zone in the Variscan belt of Sardinia. The obtained TRSCM highlighted a temperature difference, from ~470–440°C down to ~440–380°C, for the internal and external nappes, respectively. We propose that both nappes experienced syn-nappe greenschist-facies metamorphism with different TRSCM, further heating localized along the tectonic boundary in between, that is the Barbagia Thrust (BT), and finally, post-nappe stacking regional-scale folding, that deformed the TRSCM spatial distribution and drove the present-day thermal architecture.