Preprints
https://doi.org/10.5194/se-2021-3
https://doi.org/10.5194/se-2021-3

  01 Feb 2021

01 Feb 2021

Review status: this preprint is currently under review for the journal SE.

Elastic anisotropies of rocks in a subduction and exhumation setting

Michael J. Schmidtke1, Ruth Keppler1, Jacek Kossak-Glowczewski1, Nikolaus Froitzheim1, and Michael Stipp2 Michael J. Schmidtke et al.
  • 1Institut für Geowissenschaften, Rheinische Friedrich-Wilhelms-Universität, Bonn, 53115, Germany
  • 2Institute of Geosciences and Geography, Martin-Luther University, Halle (Saale), 06099, Germany

Abstract. Subduction and exhumation are key processes in the formation of orogenic systems across the world, for example, in the European Alps. For geophysical investigations of these orogens, it is essential to understand the petrophysical properties of the rocks involved. These are the result of a complex interaction of mineral composition and rock fabric including mineral textures (i.e. crystallographic preferred orientations). In this study we present texture-derived elastic anisotropy data for a representative set of different lithologies involved in the Alpine orogeny. Rock samples were collected in the Lago di Cignana area in Valtournenche, in the Italian Northwestern Alps. At this locality a wide range of units of continental and oceanic origin with varying paleogeographic affiliations and tectono-metamorphic histories are accessible. Their mineral textures were determined by time-of-flight neutron diffraction at the Frank Laboratory of Neutron Physics at the JINR in Dubna, Russia. From these data the elastic properties of the samples were calculated. The data set includes representative lithologies from a subduction-exhumation-setting. In subducted lithologies originating from the oceanic crust, the elastic anisotropies range from 1.4 to 5.0 % with average P-wave velocities of 7.01–8.24 km/s and VP / VS-ratios of 1.71–1.76. In the metasediments of the former accretionary prism the elastic anisotropies range from 4.7 to 8.2 %. This tectonic setting displays average P-wave velocities of 6.47–7.23 km/s and VP / VS-ratios of 1.60–1.76. Continental crust which is incorporated in the collisional orogen shows elastic anisotropies ranging from 1.8 to 2.8 % with average P-wave velocities of 6.42–6.51 km/s and VP / VS-ratios of 1.56–1.60. Our results suggest that mafic and felsic rocks in subduction zones at depth may be discriminated by a combination of seismic signatures: lower anisotropy and higher VP / VS ratio for mafic rocks, higher anisotropy and lower VP / VS ratio for felsic rocks and metasediments.

Michael J. Schmidtke et al.

Status: open (until 01 Apr 2021)

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  • RC1: 'Comment on se-2021-3', Anonymous Referee #1, 06 Feb 2021 reply

Michael J. Schmidtke et al.

Michael J. Schmidtke et al.

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Short summary
Properties of deformed rocks are frequently anisotropic. One of these properties is the travel time of seismic wave. In this study we measured the seismic anisotropy of different rocks, collected in the Alps. Our results show distinct differences between rocks of oceanic and those of continental origin.