This paper examines the morphotectonic and structural-geological characteristics of the Quaternary Martana Fault in the Umbria-Marche Apennines fold-and-thrust belt. This structure is more than 30 km long and comprises two segments: a N-NNW-trending longer segment and a 100 N-trending segment. After developing as a normal fault in Early Pleistocene times, the N-NNW Martana Fault segment experienced a phase of dextral faulting extending from the Early to Middle Pleistocene boundary until around 0.39 Ma, the absolute age of volcanics erupted in correspondence to releasing bends. The establishment of a stress field with a NE-ENE-trending 3 axis and NW-NNW 1 axis in Late Pleistocene to Holocene times resulted in a strong component of sinistral faulting along N-NNW-trending fault segments and almost pure normal faulting on newly formed NW-SE faults. Fresh fault scarps, the interaction of faulting with drainage systems and displacement of alluvial fan apexes provide evidence of the ongoing activity of this fault. The active left-lateral kinematic along N-NNW-trending fault segments is also revealed by the 1.8 m horizontal offset of the E-W-trending Decumanus road, at the Roman town of Carsulae. We interpret the present-day kinematics of the Martana Fault as consistent with a model connecting surface structures to the inferred north-northwest trending lithospheric shear zone marking the western boundary of the Adria Plate.
This work examines the connection between Quaternary tectonics and erosion/incision processes in the primary TuscanRomagna watershed of the Northern Apennines, which essentially coincides with the topographic culmination of the Nero Unit structural ridge. Tectonic and geomorphic information were collected in the area where this ridge is crossed by the upper Tiber River course forming a deep gorge. Structural analysis and field mapping have revealed that the region experienced polyphase tectonics with superposed thrust folding events identifiable both at the map and mesoscopic scales. Hinterland-SSW-verging thrusts and thrust-related folds deformed the whole thrust pile during the latest deformation phase. Backthrusts/backfolds controlled the development of intermountain basins nearby the main watershed during the Early Pleistocene and seemingly deformed, in the Tiber gorge, a low-relief landscape developed in the Early Pleistocene (ca. 1.1 Ma). Successively, the upper Tiber River course area and Apennines axial zone underwent a generalized uplift, which is manifested by the deep incision of palaeo-morphologies. This proposed sequence of events correlates well with the major geodynamic change of the Apennines revealed by an acceleration of uplift rates in the Middle-Late Pleistocene. This latter event may also correlate with increased rates of river incision recorded in Europe as a consequence of uplift and/or climate change.
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