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.