Plastic flow of two‐phase marbles

Abstract

[1] To quantify the effect of rigid inclusions on the flow behavior of a creeping matrix, we fabricated a suite of two-phase marbles by hot isostatically pressing mixtures of calcite and quartz powders and subsequently deformed these synthetic rocks at 300 MPa confining pressure, up to 100 MPa pore pressure, temperatures ranging from 873 to 1073 K, strain rates and stresses ranging from $10 À7 s À1 to $10 À3 s À1 and $4 MPa to 190 MPa, respectively. In constant displacement rate tests performed to axial strains of up to about 30%, we observed deformation at approximately constant stress for samples with 20% or less quartz. Even small additions of second phase significantly strengthen the aggregate, although the magnitude of the strengthening varies significantly with temperature and imposed strain rate. Investigation of the microstructure of starting samples reveals that initial porosity directly varies with quartz content and that matrix grain size inversely varies with the amount of second phase. Strength decreases modestly with increasing porosity, and consequently, strength increases as the samples compact. The effect of matrix grain size on the aggregate strength depends on the deformation conditions. The majority of tests exhibit an inverse relation between strength and matrix grain size (i.e., similar to a Hall-Petch relation), but fine-grained samples deformed at the highest temperatures exhibit decreasing strength with decreasing grain size. The addition of the quartz particles seems to result in both structural strengthening owing to decreased grain size and to transfer of load from the flowing matrix to the rigid quartz particles.

Rheology, microstructure and crystallographic preferred orientation of matrix containing a dispersed second phase: Insight from experimentally deformed ice

“…This is in agreement with previously conducted experimental studies (Wilson, 1984;Tullis and Wenk, 1994;Austin et al, 2014). In natural shear zones, GBS accompanied by diffusion creep or dislocation glide is often proposed as a process responsible for the weaker CPO in polymineralic rocks, compared to their monomineralic counterparts (e.g., Krabbendam et al, 2003;Song and Ree, 2007). A relationship between CPO and GBS activity is complex (e.g., compare: Fliervoet et al, 1997;Dimanov et al, 2007).…”

Calcite and dolomite in intrusive carbonatites. I. Textural variations

“…It has since been established experimentally that carbonate rocks become ductile under relatively low confining pressures. Under stress, the depth of brittle-ductile transition in these rocks will depend on the grain size, porosity, content and connectivity of non-carbonate material, availability of fluids, and temperature (De Bresser et al 2005;Paterson and Wong 2005;Renner et al 2007;and references therein), and can be as shallow as~1 km for a pure material (Fredrich et al 1989). A confining P of 0.5 kbar is typically cited for the reference Carrara marble (Schubnel et al 2006), which is closely similar to fine-grained anchimonomineralic (~98 % pure, with a mean grain size of 0.15 mm) calcite carbonatites.…”

Strain localization in the Morcles nappe (Helvetic Alps, Switzerland)

“…Experimental studies have shown that the addition of as little as 5 vol% uniformly dispersed quartz to fine-grained calcite aggregates increases the strength of the material (Dresen et al 1998;rybacki et al 2003;Xiao & Evans 2003;renner et al 2007). However, it is difficult to envision this strength variation resulting in contemporaneous stress variations across the shear zone, when quartz-rich limestones (Gault) are juxtaposed with pure limestones (Urgonian).…”