Shear deformation in mafic-ultramafic complex in north-western Elba island (Northern Tyrrhenian Sea)

Chiara Frassi (a), Giovanni Musumeci (a,b) & Francesco Mazzarini (c)
(a) Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria, 53, 56126 Pisa, Italy. E-mail: chiarafrassi@gmail.com (b) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Via della Faggiola 32, 56126 Pisa, Italy

The Cotoncello shear zone is developed in the mafic and ultramafic rocks cropping out in the north-western Elba island (northern Apennines). The mylonitic fabrics documented in the field, are highlighted by a pervasive mylonitic foliation and by cm- to dm-thick high-strain transpressive shear zones with a top-to-the S/SE sense of shear. At the microscopic scale, the mylonitic foliation in the high-strain shear zones is made exclusively by isoriented Mg-hornblende and tremolite. In the less deformed domains, Mg-hornblende and tremolite rich-layers enveloped small domains preserving igneous fabric and/or older mylonitic fabric. Mineral assemblage on the amphibolitic-bearing mylonitic foliation indicates that the youngest mylonitic fabric occurred under amphibolites facies condition (T > 550°C, P: 0.6-0.8 GPa).

Elba Island, metamorphic ophiolites, Northern Apennines, shear zone