Microstructure and elastic anisotropy of naturally deformed leucogneiss from a shear zone in Montalto (southern Calabria, Italy)

• DOI: 10.1144/sp332.4
• Publication Date: 2010-04-16T19:08:09Z
• Authors: Rosolino Cirrincione; Eugenio Fazio; Renée Heilbronner; Hartmut Kern; Kurt Mengel; Gaetano Ortolano; Antonino Pezzino; Rosalda Punturo
• Keywords: Shear Zone, mylonite; seismic anisotropy, seismic velocity,; leucogneiss; 01 natural sciences; 0105 earth and related environmental sciences

Abstract A strain gradient was mesoscopically recognized in sheared leucogneisses cropping out near Mount Montalto (Calabria, southern Italy) the Aspromonte–Peloritani Unit on basis of field observations. In order to investigate relationship between textural and physical anisotropy, a microstructural petrophysical study carried selected mylonites exhibiting different stages deformation. The main mineral assemblage is Qtz+Pl+Kfs+Wm, displaying S – C shear-band textures; mica-fish ribbon-like quartz are widespread. As increases K-feldspar, biotite premylonitic low phengite white mica transformed synmylonitic high quartz, accompanied by an increasing albitization. Different c -axis patterns ascribable non-coaxial progressive deformation; we suggest that deformation proceeded under greenschist- up amphibolite-facies conditions owing local increase shearing temperature. Laboratory seismic measurements were sample cubes (43 mm edged) cut according structural frame (foliation, lineation) rock. At 400 MPa room temperature averages compressional ( V p ) shear-wave velocities s very similar: 5.70–5.91 3.36–3.55 km −1 , respectively. Seismic anisotropy splitting related modal amounts constituent minerals (in particular mica) their crystallographic preferred orientation. Importantly, lowest most strained