EGU21-14906, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-14906
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evolution of melt-bearing shear zones during cooling within an upper crustal aureole: the Calamita Schists (Island of Elba, Italy)

Samuele Papeschi1, Giovanni Musumeci2,3, Omar Bartoli4, Bernardo Cesare4, Hans-Joachim Massonne5,6, and Francesco Mazzarini3
Samuele Papeschi et al.
  • 1JAMSTEC, Kochi (X-Star), Department of Earth Sciences, Kochi, Japan (s.papeschi@gmail.com)
  • 2Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
  • 3Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy
  • 4Dipartimento di Geoscienze, Università di Padova, Padua, Italy
  • 5School of Earth Sciences, China University of Geosciences, Wuhan, P.R. China
  • 6Fakultät Chemie, Universität Stuttgart, Stuttgart, Germany

The Calamita Schists in the aurole of the Late Miocene Porto Azzurro pluton underwent partial melting and HT metamorphism at P < 0.2 – 0.3 GPa and T > 650 – 700 °C, coeval with regional deformation. Deformation produced a network of shear zones that evolved from melt-present conditions to the brittle-ductile transition. Shearing at high temperature in the presence of melt allowed deformation to remain relatively distributed in wide high-strain zones. As the thermal pulse associated with the intrusion progressively faded away, deformation localized into anastomosing, mylonitic greenschist-facies shear zones surrounding lozenges of high-grade migmatitic schist. Mylonitic shear zones formed at low-angle with respect to the well-established high grade foliation preserved as a relic, oblique foliation. We show that such an extreme strain localization was determined by strain hardening of the no longer melt-bearing quartz-feldspar schist, localized embrittlement on precursory shear bands, and fluid-enhanced reaction softening that caused the breakdown of Al-silicates and the development of phyllosilicate-rich mylonitic bands. Consequently, tectonic structures with different orientation developed under the same kinematic regime, as a result of the changing physical and mechanical properties of the cooling rock volume.

How to cite: Papeschi, S., Musumeci, G., Bartoli, O., Cesare, B., Massonne, H.-J., and Mazzarini, F.: Evolution of melt-bearing shear zones during cooling within an upper crustal aureole: the Calamita Schists (Island of Elba, Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14906, https://doi.org/10.5194/egusphere-egu21-14906, 2021.

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