Characterization of granitoid and gneissic weathering profiles of the Mucone River basin (Calabria, southern Italy)

The paper deals with the development of a multidisciplinary research on weathering profiles of granitoid andgneissic rocks related to tectonic and landscape evolution of the western Sila Grande Massif (Calabria, southernItaly). Field scale observations and petrographical andmineralogical features are used to characterize in detail theweathering processes. The weathering profiles of the granitoid cut slopes are generally simple showing a progressiveweathering increase toward the top of the slopes, whereas the weathering profiles of the gneissic cutslopes are generally complexwith irregularities in the spatial distribution ofweathered horizons. The microfabricand petrographic analyses show that gneissic samples (classes V–VI of weathering grade) are characterized byhigher percentage of altered minerals and microfracture and void rather than granitoid samples (classes V–VIof weathering grade). The main mineralogical changes concern the partial transformation of biotite and the partialdestruction of feldspars (mainly plagioclases), associated with the neoformation of secondaryminerals (clayminerals and Fe-oxides) and with a substitution of the original rock fabric. Neoformed clay minerals and ferruginousproducts replaced feldspars and biotite during the most advanced weathering stage. Referred as physicalchanges coupled with chemical variations, the final results of weathering process are a soil-like material characterizedby sand–gravel grain-size fraction for the granitoid rocks and by both silt–clay and sand–silt grain-sizefraction for the gneissic rocks. This generally produces a greater value of the SGI (Sand Generation Index) forgranitoids and explains the great productivity in sandy deposits of this lithology.