Geological map, balanced and restored cross-sections, and 3D geological model of the Monte Fema area, Umbria-Marche Apennines (Italy)

Abstract

The Mt. Fema area is located within the 1:50,000 scale Sheet 325-Visso of the CARG project, in the Umbria-Marche Apennines. Here, inherited pre-orogenic deformation and multi-layered mechanical stratigraphy affect mountain belt evolution and cause along-and across-strike changes in structural architecture. Further complexity is caused by post-orogenic extensional tectonics dissecting the fold and thrust belt. In this work, we combined classical field methodologies with digital mapping and drone surveys to produce a 1:10,000 geological map of the Mt. Fema area. The resulting map was integrated with a 10 m-cell size DEM in a 3D environment to construct four balanced cross-sections that were used to document structural style and stratigraphic variations. One section was restored to quantify the amount of deformation related to both Neogene orogenic shortening and multiple extensional phases affecting the area. Ultimately, we built a 3D geological model to investigate the subsurface geometrical arrangement of strata and faults of different generations, thus the overall structural architecture of the fold and thrust belt. According to our interpretation, the Mt. Fema thrust system is characterised by relatively limited displacement (cumulative dip separation ranging from ~100 m to the north in Val di Tazza to ~500 m to the south in Valnerina). Reactivation of inherited normal faults was likely precluded because of their unfavourable orientation with respect to W-dipping thrusts. Inherited basin structure and mechanical stratigraphy govern folding by buckling mechanism, which in turn controls the locus of thrust propagation. Normal faults dissect the crestal region of the Mt. Fema anticline. These structures do not show evidence of surface faulting during recent seismic sequences, although earthquake epicentres fall within the study area. Our work provides new insights into the 3D structural architecture, timing, and kinematics of a key sector of the Umbria-Marche Apennines, with implications for a better understanding of the role of structural inheritance and subsequent extensional tectonics in the evolution of fold and thrust belts.