Quantitative 3D microstructural analysis of naturally deformed amphibolite from the Southern Alps (Italy): microstructures, CPO and seismic anisotropy from a fossil extensional margin
Michele Zucali, Valentina Barberini, Marco Voltolini, Bachir Ouladdiaf, Daniel Chateigner, Lucia Mancini, Luca Lutterotti, 2016. "Quantitative 3D microstructural analysis of naturally deformed amphibolite from the Southern Alps (Italy): microstructures, CPO and seismic anisotropy from a fossil extensional margin", Rock Deformation from Field, Experiments and Theory: A Volume in Honour of Ernie Rutter, D. R. Faulkner, E. Mariani, J. Mecklenburgh
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The anisotropy of a rock is intimately related to the development of shape-preferred orientations (SPOs) and crystallographic-preferred orientations (CPOs). Quantifying the three-dimensional (3D) CPOs and SPOs in natural rocks is therefore critical for understanding the processes underlying the development of anisotropy. In this work, we present a CPO study of six amphibolite samples from the western Southern Alps (Italy) that have been characterized previously. Quantitative texture analyses using neutron diffraction data provided 3D CPOs for amphibole and plagioclase and were used to calculate seismic properties. We describe the relations between mesoscopic foliation and lineation, crystallographic fabrics and seismic anisotropies for lower–middle crust amphibolites. Based on these relations and in the context of lower–middle crust within fossil extensional margin, we suggest that seismic profiles should display large-scale geological features commonly present in extensional tectonics, such as folds and shear zones, rather than flat-lying structures. Moreover, from the integration of CPOs with geological data, we observe that samples from the Strona Ceneri boundary are characterized by a granulite to amphibolite facies transition while those from the Scisti dei Laghi only record the amphibolite facies evolution, supporting the idea of two independent tectono-metamorphic units pre-dating the amphibolite re-equilibration.
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Ernie Rutter has made, and continues to make, a significant impact in the field of rock deformation. He has studied brittle and plastic deformation processes that occur within both the oceanic and continental crust, as well as other key properties such as the permeability and seismic velocities of these rocks. His approach has been one that integrates field observations, laboratory experiments and theoretical analyses. This volume celebrates Ernie’s key contribution to rock deformation and structural geology by bringing together a collection of papers that represent this broad approach. The papers within the volume address key issues that remain within these fields. These range from fundamental studies of brittle and plastic behaviour along with the resultant structures and microstructures from both the field and laboratory, to applied problems where a better understanding of the deformation and properties of the crust is still needed.