present-day geodynamic microplate puzzle of the western Mediterranean area, acting as one of the principal controllingmechanisms for the asymmetric openings of the back arc proto-oceaninc basins (e.g. Vavilov basin; Ligure-ProvenzaleBasin, Rosenbaum and Lister, 2004).The Palmi Shear Zone (PSZ) probably represents an outcropping relic branch of one of these strike-slip regionalscaletectonic structure. In particular, it constitutes the limit between the very shortened Aspromonte Massif nappe-likeedifice and the quasi-complete crustal section of the Serre Massif, contributing in part to the the formation of thecomposite framework of present-day Calabrian Peloritani Orogen (CPO), a ribbon-like orogenic segment, locallycharacterized by lateral juxtaposition of metamorphic rocks with different tectono-metamorphic evolution (Pezzino etal., 2008; Angì et al., 2010).PSZ is exposed with an average thickness of 400 mt withrocks showing a very steeply mylonitic foliation, involvingessentially skarns, and subordinately migmatititic paragneisses and tonalites, which are then characterized by thedevelopment of a pervasive mylonitic foliation and of a stretching lineation ranging from W-E, to NW-SE. Skarns arealways mylonitized acting as a weakening layer, while migmatititic paragneisses and tonalites are characterized both bypervasive mylonitic foliation, essentially controlled by quartz-dominated rock rheology, as well as by local low-straineddomains manteled by mylonitic skarns, forming centimeter- to metre-sized asymetrical porphyiroclasts, variablycostraining top-to-ESE and WNW sense of shear in the present-day geographic coordinates.The rheological un-homogeneity of the involved mylonitic rocks produces a complex sheath-folding systemcharacterized by the widespread presence of oblique fold with horizontal axis mostly parallel with the stretchinglineation, locally varying to quasi-vertical inclination. Local presence of eye folding sections also occurs, suggesting asthe investigated shear zone may be linked to a progressive strain of the same event rather than multiple deformationalones.Finally, quartz c-axis orientation pattern analysis of the syn-shearing quartz-rich levels seems to be consistent with atop to ESE shearing sense, in green-schist facies conditions (400°- 500°C). These evidences highlight an Africa vergingmovement of the southern CPO since the Cretaceous-Paleocene boundary and still active up to 56 to 51 Ma asconstrained by the Rb-Sr age obtained from whole mica analysis of mylonitic tonalite (Prosser et al., 2003).
Regional-scale strike-slip tectonics during the evolution of the Palmi Shear Zone (southern Italy, Calabria)
ORTOLANO, GAETANO;CIRRINCIONE, ROSOLINO;FAZIO, EUGENIO
2015-01-01
Abstract
present-day geodynamic microplate puzzle of the western Mediterranean area, acting as one of the principal controllingmechanisms for the asymmetric openings of the back arc proto-oceaninc basins (e.g. Vavilov basin; Ligure-ProvenzaleBasin, Rosenbaum and Lister, 2004).The Palmi Shear Zone (PSZ) probably represents an outcropping relic branch of one of these strike-slip regionalscaletectonic structure. In particular, it constitutes the limit between the very shortened Aspromonte Massif nappe-likeedifice and the quasi-complete crustal section of the Serre Massif, contributing in part to the the formation of thecomposite framework of present-day Calabrian Peloritani Orogen (CPO), a ribbon-like orogenic segment, locallycharacterized by lateral juxtaposition of metamorphic rocks with different tectono-metamorphic evolution (Pezzino etal., 2008; Angì et al., 2010).PSZ is exposed with an average thickness of 400 mt withrocks showing a very steeply mylonitic foliation, involvingessentially skarns, and subordinately migmatititic paragneisses and tonalites, which are then characterized by thedevelopment of a pervasive mylonitic foliation and of a stretching lineation ranging from W-E, to NW-SE. Skarns arealways mylonitized acting as a weakening layer, while migmatititic paragneisses and tonalites are characterized both bypervasive mylonitic foliation, essentially controlled by quartz-dominated rock rheology, as well as by local low-straineddomains manteled by mylonitic skarns, forming centimeter- to metre-sized asymetrical porphyiroclasts, variablycostraining top-to-ESE and WNW sense of shear in the present-day geographic coordinates.The rheological un-homogeneity of the involved mylonitic rocks produces a complex sheath-folding systemcharacterized by the widespread presence of oblique fold with horizontal axis mostly parallel with the stretchinglineation, locally varying to quasi-vertical inclination. Local presence of eye folding sections also occurs, suggesting asthe investigated shear zone may be linked to a progressive strain of the same event rather than multiple deformationalones.Finally, quartz c-axis orientation pattern analysis of the syn-shearing quartz-rich levels seems to be consistent with atop to ESE shearing sense, in green-schist facies conditions (400°- 500°C). These evidences highlight an Africa vergingmovement of the southern CPO since the Cretaceous-Paleocene boundary and still active up to 56 to 51 Ma asconstrained by the Rb-Sr age obtained from whole mica analysis of mylonitic tonalite (Prosser et al., 2003).File | Dimensione | Formato | |
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