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High-temperature shear zone formation in Carrara marble

  • Rock deformation at depths in the Earth’s crust is often localized in high temperature shear zones occurring at different scales in a variety of lithologies. The presence of material heterogeneities is known to trigger shear zone development, but the mechanisms controlling initiation and evolution of localization are not fully understood. To investigate the effect of loading conditions on shear zone nucleation along heterogeneities, we performed torsion experiments under constant twist rate (CTR) and constant torque (CT) conditions in a Paterson-type deformation apparatus. The sample assemblage consisted of cylindrical Carrara marble specimens containing a thin plate of Solnhofen limestone perpendicular to the cylinder’s longitudinal axis. Under experimental conditions (900 °C, 400 MPa confining pressure), samples were plastically deformed and limestone is about 9 times weaker than marble, acting as a weak inclusion in a strong matrix. CTR experiments were performed at maximum bulk shear strain rates of ~ 2*10-4s-1, yielding peakRock deformation at depths in the Earth’s crust is often localized in high temperature shear zones occurring at different scales in a variety of lithologies. The presence of material heterogeneities is known to trigger shear zone development, but the mechanisms controlling initiation and evolution of localization are not fully understood. To investigate the effect of loading conditions on shear zone nucleation along heterogeneities, we performed torsion experiments under constant twist rate (CTR) and constant torque (CT) conditions in a Paterson-type deformation apparatus. The sample assemblage consisted of cylindrical Carrara marble specimens containing a thin plate of Solnhofen limestone perpendicular to the cylinder’s longitudinal axis. Under experimental conditions (900 °C, 400 MPa confining pressure), samples were plastically deformed and limestone is about 9 times weaker than marble, acting as a weak inclusion in a strong matrix. CTR experiments were performed at maximum bulk shear strain rates of ~ 2*10-4s-1, yielding peak shear stresses of ~ 20 MPa. CT tests were conducted at shear stresses of ~ 20 MPa resulting in bulk shear strain rates of 1-4*10-4s-1. Experiments were terminated at maximum bulk shear strains of ~ 0.3 and 1.0.Strain was localized within the Carrara marble in front of the inclusion in an area of strongly deformed grains and intense grain size reduction. Locally, evidences for coexisting brittle deformation are also observed regardless of the imposed loading conditions. The local shear strain at the inclusion tipis up to 30 times higher than the strain in the adjacent host rock, rapidly dropping to 5times higher at larger distance from the inclusion. At both investigated bulk strains, the evolution of microstructural and textural parameters is independent of loading conditions. Ourresults suggest that loading conditions do not significantly affect material heterogeneity-induced strain localization during its nucleation and transient stages.show moreshow less

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Metadaten
Author:Livia Nardini, Erik Rybacki, Maximilian J.E.A. Döhmann, Luiz F.G. MoralesORCiD, Sascha BruneORCiDGND, Georg DresenGND
DOI:https://doi.org/10.1016/j.tecto.2018.10.022
ISSN:0040-1951
Parent Title (English):Tectonophysics
Subtitle (English):The effect of loading conditions
Publisher:Elsevier
Place of publication:Amsterdam [u.a.]
Document Type:Article
Language:English
Date of first Publication:2018/07/18
Year of Completion:2018
Release Date:2020/09/01
Tag:Shear zones; loading conditions; localization; marble; torsion
Volume:749
Page Number:19
First Page:120
Last Page:139
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Geowissenschaften
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Peer Review:Referiert
Licence (German):License LogoKeine Nutzungslizenz vergeben - es gilt das deutsche Urheberrecht
Notes extern:This article is part of this cumulative dissertation