Recent reverse faults and landslides in granitoid weathered profiles, Serre Mountains (southern Calabria, Italy)

It is rarely possible to identify reverse faults that bring portions of substratum solid rock to lie above decomposed rock. Only where the differences between the fresh rock and weathered rock are very clear is it possible to recognise such faults. A “reverse profile” is defined as a slope profile in which fresh rock (granitoids) overlaps rocks which have been greatly altered by mature weathering (saprolite of granitoids). Such a profile occurs along the slopes of Molini Valley to the south of the village of Fabrizia (Calabria, southern Italy) and we interpret the morphological, mechanical and structural evidence as typical of a reverse fault. The mineral-petrographic analysis of the grus on the bed of the fault and of the cover of relatively fresh rock (Schmidt hammer 18–35) confirms that the granular framework can be attributed to subaerial alteration and not to mechanical deformation. The study area is located at the centre of the largest kinematic body of southern Calabria (the Serre massif-exclusively granitoids) until now considered to be only affected by extensional tectonics, creating high angle normal faults. In this area the tectonic processes, the thickness and spread of granitoid weathering mantles and the depth of the valleys, give rise to several landslides. These are generally translational slides with ample cut surfaces between the weathered body and the underlying fresh rock; as a consequence, very large deposits in the valleys can be found, mostly produced by debris flow processes. At the foot of the slopes around Fabrizia, coarse debris avalanches (with cobbles having a volume of over 0.3–0.4 m3) are occasionally observed, unless there is widespread development of a “reverse weathering profile” on the slopes above.