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 ductile–brittle 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. Copyright © 2008 John Wiley & Sons, Ltd.