The Sabina strike-slip fault at the ‘ancient marble’ quarry of Cottanello (central Apennine, Italy)

Abstract

The Geosite is a N10E strike-slip fault (Sabina Fault: Alfonsi et al. 1991), which crops out continuously within the western part of the Sabina area, in central Apennines, Italy. The shear zone of Sabina Fault is spectacularly exposed in an abandoned quarry, north of the village of Cottanello (42°24.935′N, 12°41.318′E; Fig. 1a). Here, the Sabina fault system shows a peculiar petrofabric texture within the reddish marly limestones (Scaglia Rossa Formation) resulting in severe pressure solution and subsequent recrystallization of calcites, within extensional fractures and inside S-C structures whose frequency increases towards the main fault surface. These phenomena produced a peculiar lithological type, called Marmo di Cottanello (marbe of Cottanello), where the term ‘marble’ is used to describe a decorative stone used in antiquity. Indeed, this stone was exported regionally in the Roman Imperial period and extensively used in the Renaissance and in the Baroque age (Pensabene et al. 2015; Brilli et al. 2017): Bernini and Borromini employed it to ornate famous Roman monuments such as the columns inside St Peter’s, Sant’Andrea al Quirinale or S. Agnese in Agone Church in Rome (Fig. 1c). The Sabina strike-slip fault has been active since the late Miocene to the latest Pleistocene, and it is still tectonically active. It shows a dextral movement with a recognizable elongation of ~ 40 km, accompanied by a swarm of splays with differential dips from 90° to 30° developed up to hundreds of meters away from the main fault scarps (Alfonsi et al. 1990, 1991). This structure has inverted a Jurassic fault that truncated the Sabine pelagic plateau to the east, with kinematics from dextral transpressive to transcurrent (Pierantoni 1997). Alfonsi et al. (1991) related the Sabina Fault with crustal strike-slip tectonics, which post-date the chain development, responsible for the rotation of the folds and thrusts until they assumed their present day direction (Mattei et al. 1992). Stable isotope analysis of calcite‐filling fractures suggest the host rock strongly influences the composition of vein fillings under confined system condition, common to both transpressive faults and thrusts. Open system conditions develop only under a clearly extensional tectonic regime in the more recent fracture systems (Maiorani et al. 1992; Conti et al. 2001). The Sabina Fault, as exposed at the Cottanello quarry, is a remarkable geological feature because it represents one of the most emblematic tectonic elements in the central sector of the Apennine chain; the pervasive microstructures such as vein systems, cleavage planes and stylolitic surfaces, generated besides the major deformational features, probably represent the most complete synthesis of the geological events that have built the Apennine chain (Funiciello and Mattei 1991).