Dislocation creep of polycrystalline dolomite

Influence of stress and strain on dolomite rim growth: a comparative study

“…Since carbonates are present in a broad range of environments, their behavior is of great interest in the formation of mylonitic shear zones and subduction zones (Holyoke et al 2013(Holyoke et al , 2014. In this study, we observed the formation of fine-grained polycrystalline dolomite and magnesio-calcite in between single crystals of calcite and magnesite during deformation.…”

“…Davis et al (2008) observed diffusion creep of fine-grained (2-12 µm) dolomite in triaxial compression experiments at temperatures >700 °C, whereas coarse-grained (240 µm) dolomite deformed by dislocation creep. In the temperature range of 700-1000 °C, Holyoke et al (2013) noticed a transition from dislocation creep to diffusion creep at high strain, induced by the development of fine-grained (<10 µm) shear zones associated with strain weakening. In our experiments, however, particularly in dolomite regions of chemical disequilibrium close to magnesio-calcite and those of high stress-strain, grain boundary bulging occurs by the reduction in high dislocation densities along grain boundaries, potentially leading to the observed slight increase in low-angle grain boundaries with applied stress (Fig.…”

“…Here, we focus on the CaCO 3 -MgCO 3 system since carbonates are of great geological interest with calcite (CaCO 3 ) and dolomite (CaMg [CO 3 ] 2 ) often found in crustal shear zones and magnesite (MgCO 3 ) occurring in subduction zones and ultrahigh pressure metamorphic terranes (Holyoke et al 2013(Holyoke et al , 2014. In a previous study (Helpa et al 2014), we investigated diffusion-controlled dolomite reaction rim growth at the contacts of oriented calcite and magnesite single crystals at isostatic conditions of pressure P = 400 MPa, T = 750-850 °C and t = 3-146 h. Polycrystalline dolomite reaction rims showed a palisade-like microstructure in contact with magnesite and granular grains in contact with calcite.…”

“…Diffusion creep appears to be independent of the magnesium content, but for dislocation creep, higher magnesium concentrations increase the strength of magnesio-calcite. Constitutive equations for creep of dolomite in both regimes are provided by Holyoke et al (2013), partially based on measurements taken by Davis et al (2008) andDelle Piane et al (2008).…”

“…Therefore, dislocation-accommodated grain boundary sliding with strain rates in between those of dislocation and grain boundary diffusion creep (e.g., Hirth and Kohlstedt 2003;Hansen et al 2011) may be prevailing in magnesio-calcite and granular dolomite, which agrees with our microstructural and textural observations. In addition, due to end effects, the mechanical behavior of thin layers is presumably different than of thick aggregates, which makes Holyoke et al (2014), for dolomite by Holyoke et al (2013), for magnesio-calcite (Mg-Cal; Mg-Cal 70/80) by Herwegh et al (2003) and Xu et al (2009), for calcite single crystals (Cal SC) by de Bresser (1991), and for Cararra marble by Schmid et al (1980) Page 17 of 21 16 application of the flow laws more complicate. For example, frictional sliding effects (Ji et al 2000(Ji et al , 2005 or inhomogeneous stress distributions (e.g., Turner et al 1954;Götze et al 2010) at contact interfaces will likely influence the deformation behavior and composite strength.…”