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Pre-orogenic High Temperature Shear Zones in an Ophiolite Complex (Bracco Massif, Northern Apennines, Italy)

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Mantle and Lower Crust Exposed in Oceanic Ridges and in Ophiolites

Part of the book series: Petrology and Structural Geology ((PESG,volume 6))

Abstract

This paper presents the first results of a structurally-oriented study of pre-orogenic high temperature shear zone structures which are preserved in the Northern Apennines ophiolites. A detailed analysis is made of the geometry, areal distribution and kinematics of upper amphibolite facies shear zones present in the gabbroic Bracco Massif. The high temperature shear zones show distinct deformation gradients, and three characteristic fabric types are recognized: porphyroclastic coarse grained metagabbro mylonites (fabric type 1), banded ultramylonites (fabric type 2), and “flinty” ultramylonites (fabric type 3). Microstructural observations suggest that the deformation in the gneissic mylonite types (fabric types 1 and 2) was dominated by dislocation creep, whilst a possible grainsize-sensitive flow mechanism may have been important in the very fine grained “flinty” ultramylonites (fabric type 3). Reconstruction of the shear zones into their presumed original orientations suggests that they developed as low- to medium-angle extensional fault zones. This has important implications for the inferred processes of ophiolite generation.

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Authors and Affiliations

  1. Dipartimento di Scienze della Terra, Università di Pisa, 56126, Pisa, Italy

    Giancarlo Molli

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  1. Giancarlo Molli
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Editors and Affiliations

  1. Faculty of Earth Sciences, Geodynamics Research Institute, Utrecht, The Netherlands

    R. L. M. Vissers

  2. Laboratoire de Tectonophysique, Université des Sciences et Techniques du Languedoc, Montpellier, France

    A. Nicolas

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© 1995 Springer Science+Business Media Dordrecht

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Molli, G. (1995). Pre-orogenic High Temperature Shear Zones in an Ophiolite Complex (Bracco Massif, Northern Apennines, Italy). In: Vissers, R.L.M., Nicolas, A. (eds) Mantle and Lower Crust Exposed in Oceanic Ridges and in Ophiolites. Petrology and Structural Geology, vol 6. Springer, Dordrecht. https://doi.org/10.1007/978-94-015-8585-9_6

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  • DOI: https://doi.org/10.1007/978-94-015-8585-9_6

  • Publisher Name: Springer, Dordrecht

  • Print ISBN: 978-90-481-4557-7

  • Online ISBN: 978-94-015-8585-9

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