Fault‐slip analysis in the metaophiolites of the Voltri Massif: constraints for the tectonic evolution at the Alps/Apennine boundary

Abstract

The metaophiolitic Voltri Massif underwent a complex tectono-metamorphic evolution, resulting from subduction to collision events during the Alpine orogenic cycle, and was subsequently involved in the first stages of the Apennine Orogeny. So this is a key area to investigate the late orogenic Alpine tectonics and its time relationship with the first Apenninic deformation events.We performed detailed mapping, fault-slip analysis and study of fault rocks in a study area located at the eastern border of the Voltri Massif. Here we recognized two main generations of reverse shear zones (RSZ). The first one (RSZ1) is associated to mylonites and protomylonites in greenschist to low-greenschist metamorphic facies and is characterized by a ductile to ductilebrittle behaviour; RSZ1 display either top-to-N-NW or to-SW kinematics. The second generation of reverse shear zones (RSZ2) is characterized by fault breccia, crush breccia or protocataclasite; RSZ2 sense of tectonic transport ranges from top-to-NW, -SW and -NE.RSZ1 structures are locally folded by 10 m-scale, open chevron folds with fold axes gently plunging to SW that likely represent the last phases of deformation during Alpine collision.RSZ2 structures locally reactivate RSZ1, with a more brittle behaviour and produce a huge volume of fault rock. They are coeval with low-greenschist to zeolite-facies metamorphic conditions. The RSZ2 fit a transpressional regime active at the eastern border of the Voltri Massif at least during the late Oligocene-early Miocene.

Tectono‐sedimentary evolution of the Tertiary Piedmont Basin (NW Italy) within the Oligo–Miocene central Mediterranean geodynamics

“…Indeed, in the Cuneo area, localized transpressive structures, involving both the basement and the Oligocene strata of the TPB, were detected: strike‐slip faults with flower geometry influenced the deposition of the Oligocene sub‐basins and are sealed by Miocene sediments. Strike‐slip tectonics is furthermore testified in the Voltri massif, where the Sestri‐Voltaggio fault system shows dextral kinematics since the Chattian [ Capponi et al ., ; Federico et al ., ].…”

“…Since the Oligocene, in the metamorphic basement, deformation in frictional conditions brought to the development of the D4–D5 systems of cataclastic‐gouge fault zones [Table ; Vanossi et al ., ; Crispini et al ., ; Federico et al ., ; Vignaroli et al ., ; Bonini et al ., ]. The stress/strain regime and the timing of these phases are poorly resolved as they resulted from the overlap of several tectonic events, including the Early–Middle Miocene oceanic spreading of the Liguro‐Provençal basin, the coeval 50° of vertical rotation [ Maffione et al ., ] of the Ligurian Alps‐TPB system [ Vanossi et al ., ], and the drifting of the Corsica‐Sardinia block [ Gattacceca et al ., ].…”

“…To the east, the Sestri‐Voltaggio Fault represents a km‐scale N–S discontinuity that played different roles in different stages of the tectonic evolution of the area [ Crispini and Capponi , ; Vignaroli et al ., ]. Generated as a mylonitic shear zone during the metamorphic deformational phases (D1–D3, Table ), it records an Oligo–Miocene brittle dextral strike‐slip kinematics [ Capponi et al ., ; Federico et al ., ].…”

Comments on the paper ‘Subduction of a fossil slow–ultraslow spreading ocean: a petrology-constrained geodynamic model based on the Voltri Massif, Ligurian Alps, NW Italy’ by G. B. Piccardo

“…Piccardo's (2013) introduction claims that, after the geologic-petrologic paper by Chiesa et al (1975), three decades of little attention to the geodynamic history of the Voltri Massif followed, which was only recently highlighted by the structural-petrologic papers by Vignaroli et al (2008) and Piccardo (2013). However, over the last two decades, relatively broad, well-accepted geodynamic pictures regarding the evolution of the Voltri meta-ophiolites + Erro-Tobbio have been presented in a number of publications (Hoogerduijng Vissers et al 1991;Hoogerduijn Strating et al 1993;Scambelluri et al 1995;Hermann et al 2000;Brouwer et al 2002Brouwer et al , 2004Capponi and Crispini 2002;Federico et al 2005Federico et al , 2007Federico et al , 2009Rampone et al 2005;Rampone and Borghini 2008;Healy et al 2009;John et al 2011;Kendrick et al 2011).…”

Anatomy of the Ligure-Piemontese subduction system: evidence from Late Cretaceous–middle Eocene convergent margin deposits in the Northern Apennines, Italy

“…The Sestri-Voltaggio line has been regarded as an east-dipping, low-angle normal fault of early Tertiary age successively reworked in the Oligo-Miocene time (Hoogerduijn Strating 1994). Very recently, Capponi et al (2009) and Federico et al (2009) have provided evidence for a dextral transpression along the Sestri-Voltaggio line during the Oligo-Miocene, interpreted as related to the indenter of Adria into the Western Alps arc. Despite the different interpretations, a pressure gap of about 8 kbars can be detected across the Sestri-Voltaggio line between the Voltri Group and the IL units.…”