Elastic anisotropies of deformed upper crustal rocks in the Alps

Abstract. The crust within collisional orogens is very heterogeneous both in composition and grade of deformation, leading to highly variable physical properties at small scales. This causes difficulties for seismic investigations tectonic structures depth since the diverse partially strong upper crustal anisotropy might overprint signal deeper anisotropic mantle. In this study, we characterize range elastic anisotropies deformed rocks Alps. Furthermore, model average these their changes with increasing due closure microcracks. For that, pre-Alpine Adula Nappe central Alps, which were intensely during Alpine orogeny, sampled. two major rock types found are orthogneisses paragneisses; however, lenses metabasites marbles also occur. Crystallographic preferred orientations (CPOs) volume fractions minerals samples measured using time-of-flight neutron diffraction. Combined single crystal used rocks. sample set shows a wide different velocity patterns even same lithology, microstructural heterogeneity To approximate an units, picked common CPO forming gneiss representing most lithology. These data determine typical Average mineral percentages calculation. addition, ultrasonic measurements confining pressures performed. as well microcrack determined thin sections microcracks depth. Microcracks closed approximately 740 MPa yielding 4 % gneiss. value approximation, can be models lithospheric scale. At or smaller scale, local variations lithology deformation displayed by need considered. larger-scale structural such layering, intrusions brittle faults have included any crustal-scale model.