Vorticity analysis of the Palmi shear zone mylonites: new insights for the Alpine tectonic evolution of the Calabria–Peloritani terrane (southern Italy)

Abstract

New microstructural data on the mylonites from the well-exposed Palmi shear zone (southern Calabria) are presented with the aim to shed light on both the kinematics and the geometry of the southwestern branch of the Alpine belt during Eocene. In the study area, located between the Sardinia-Corsica block and the Calabria-Peloritani terrane, previous large-scale geodynamic reconstructions suggest the presence of strike-slip or transform fault zones dissecting the southwestern branch of the Alpine belt. However, there are no field data supporting the occurrence of these structures. This paper uses vorticity analysis technique based on the aspect ratio and the long axis orientation of rigid porphyroclasts in mylonitic marbles and mylonitic granitoids, to estimate the contribution of pure and simple shear of deformation during the movement of the Palmi shear zone. Porphyroclasts aspect ratio and orientation were measured on thin sections using image analysis. Estimates of the vorticity number, W m , indicate that the Palmi shear zone recorded general shear with a contribution of pure shear of c. 65%. Then, the Palmi shear zone can be interpreted as a segment of a left-lateral transpressive bend along the southern termination of the Eocene Alpine front.

Kinematic and geochronological constraints on shear deformation in the Ferriere-Mollières shear zone (Argentera-Mercantour Massif, Western Alps): implications for the evolution of the Southern European Variscan Belt

“…Deformation in shear zones is often approximate to simple shear, especially in high-strain zones (Passchier 1987(Passchier , 1991Iacopini et al, 2010Iacopini et al, , 2011. However, a significative component of pure shear has been detected in many regional-scale shear zones around the world, under various metamorphic conditions Palmeri, 2002, Carosi et al, 2005;Carosi et al, 2006Carosi et al, , 2007Festa et al, 2016;Goscombe et al, 2003Goscombe et al, , 2005Iacopini et al, 2008;Kurz and Northrup, 2008;Larson and Godin, 2009;Law et al, 2004;Li et al, 2016;Nabavi et al, 2016;Sarkarinejad and Azizi, 2008;Sarkarinejad et al, 2015;Wu et al, 2016;Xypolias and Kokkalas, 2006;Zang and Teyssier, 2013).…”

Hercynian subduction‐related processes within the metamorphic continental crust in Calabria (southern Italy)

“…After these events, the continental crust underwent cooling (Graessner, Schenk, Brocker, & Mezger, 2000;Schenk, 1980) and some Alpine Eocene ductile shear zones developed bounding the Serre Massif crustal block (Cirrincione et al, 2015;Festa et al, 2016;Langone, Gueguen, Prosser, Caggianelli, & Rottura, 2006;Schenk, 1980). Finally, a further exhumation stage took place starting from the Oligocene, as indicated by apatite and zircon fission-track ages (Thomson, 1994), and a crustal tilting of ~40° occurred, determining the present-day SE-dipping and exposition of the Early Permian crustal block in the Serre Massif (Festa, Di Battista, Caggianelli, & Liotta, 2003;Görler, 1978).…”

Ductile Shearing and Focussed Rejuvenation: Records of High-P (eo-)Alpine Metamorphism in the Variscan Lower Crust (Serre Massif, Calabria—Southern Italy)

“…However, because post-Variscan metamorphism and tectonics in the Calabria-Peloritani terrane are framed from Meso-to Neo-alpine [12,[15][16][17]19,[21][22][23][24][25] ages, the possible eo-Alpine…”

“…Continental units belong to the Variscan crystalline basement, and were locally overprinted by Alpine metamorphism up to 0.9-1.0 GPa and 560-590 • C [19][20][21][22][23][24], rarely reaching the conditions of the amphibolite-eclogite facies transition [25]. According to [26], the metamorphic overprint of the continental crust derived units occurred between 45 Ma and 33 Ma.…”