Abstract
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 ∗ 10−4 s−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 ∗ 10−4 s−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 tip is up to 30 times higher than the strain in the adjacent host rock, rapidly dropping to 5 times higher at larger distance from the inclusion. At both bulk strains, the evolution of microstructural and textural parameters is independent of loading conditions. Our results suggest that loading conditions do not significantly affect material heterogeneity-induced strain localization during its nucleation and transient stages.
Highlights
Localization of deformation in the deep crust and mantle is a key mechanism involved in the formation of tectonic plates and mountain belts on our planet (Tackley, 2000; Schubert et al, 2001; Bercovici and Karato, 2002; Bercovici, 2003; Regenauer-Lieb & Yuen, 2003; 5 Regenauer-Lieb and Yuen, 2004)
We experimentally investigate the effects of different loading conditions 45 on the nucleation and evolution of heterogeneity-induced high temperature shear zones in a carbonate system
165 We present the results from four experiments, two of which were run at constant twist rate and two at constant torque conditions (CTR and CT, respectively, equivalent to constant strain rate and constant stress) in the torsion setup of a Paterson-type gas deformation apparatus
Summary
Localization of deformation in the deep crust and mantle is a key mechanism involved in the formation of tectonic plates and mountain belts on our planet (Tackley, 2000; Schubert et al, 2001; Bercovici and Karato, 2002; Bercovici, 2003; Regenauer-Lieb & Yuen, 2003; 5 Regenauer-Lieb and Yuen, 2004). The effects of material properties and boundary conditions on the mechanical and microstructural evolution associated with strain localization and weakening are not yet understood and only a few experimental studies exist at present. The effect of the imposed loading conditions on 30 the efficiency of localization within homogeneous materials has largely been investigated in theoretical models (Fressengeas & Molinari, 1987; Leroy & Molinari, 1992; Paterson, 2007) but experimental studies of ductile localization induced by some of the aforementioned mechanisms of rheological weakening have not yet been performed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
