Abstract

Within the western part of the Sabina area, 50 km north of Rome, a N10E strike-slip fault (Sabina Fault), which outcrops continuously from the village of Casperia to Stroncone, is recognized. The Sabina Fault appears to continue northward across the tectonic basin of Terni and along the Umbrian Apennines toward Spoleto, whereas southward it is covered by Plio-Pleistocene marine deposits, alluvial fans of the Tiber river, and Alban Hills volcanites. The role of strike-slip faulting is generally inferred in several models of Apennine structural evolution, but has not yet been recognized in a continuous and clear structure in the field element. The aim of this paper is to introduce this tectonic feature and the related strain pattern which is probably connected with the recent geodinamical evolution of Central Italy. The Sabina strike-slip fault has been active since the late Miocene to the latest Pleistocene in a number of different pulses. It shows a dextral movement with a recognizable elongation of almost 40 km, accompanied by a swarm of splays with differential dips from 90 degrees to 30 degrees developed up to hundreds of meters away from the main fault scarp. A set of open folds whose axial planes generally dip towards the east are also present, the results of the changing strike of the main fault producing small compressive volumes. The frequency of stylolitic cleavage systems increases toward the main fault surface with a production of redeposited calcites sigmoidal bodies, which create a peculiar petrofabric texture within the "Scaglia rossa" beds. These structures produce a peculiar and unique lithological type that was used in the development of Roman and Baroque historical monuments as the, so called, "Marmo di Cottanello". The vertical displacement of the base of Pleistocene sediments and coastlines is 100 m. An en-echelon system of fractures was recognized in Pliocene marine units which outcrop in the Campagna Romana. They are associated to strike-slip faulting that could represent the southermost extension of the Sabina Fault. <sup>13</sup> C and <sup>18</sup> O data show a differential role of fluids within extensive fracture swarms in Mesozoic Scaglia and in Lower Pliocene clays to that found in sigmoidal recrystallized calcite bodies. This result confirms the polyphase tectonic activity of the Sabina Fault.

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