TY  - JOUR
A1  - Nardini, Livia
A1  - Rybacki, Erik
A1  - Döhmann, Maximilian J.E.A.
A1  - Morales, Luiz F.G.
A1  - Brune, Sascha
A1  - Dresen, Georg
T1  - High-temperature shear zone formation in Carrara marble
BT  - The effect of loading conditions
JF  - Tectonophysics
N2  - 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 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.
KW  - Shear zones
KW  - localization
KW  - marble
KW  - torsion
KW  - loading conditions
Y1  - 2018
U6  - https://doi.org/10.1016/j.tecto.2018.10.022
SN  - 0040-1951
VL  - 749
SP  - 120
EP  - 139
PB  - Elsevier
CY  - Amsterdam [u.a.]
ER  -