Experimental study of grain-size sensitive flow of synthetic, hot-pressed calcite rocks

Abstract

Synthetic calcite rocks of controlled grain-size were prepared by crushing large, clear calcite crystals, centrifuged to separate restricted grain-size fractions, cold-pressed and then hot-pressed to produce low-porosity polycrystals of mean grain-size covering the range 2–40 µm. These were deformed dry over the range 400–700°C, mainly at 200 MPa confining pressure, to investigate the onset with decreasing grain-size of grain-size sensitive flow. The deformation of the fine-grained material can be described by a flow law of the form ė = A exp (− H/RT ) σ n d m in which at low stresses (<25 MPa differential stress) A = 10 4.9 , H = 190 kJ mol −1 , n = 1.7 and m = −1.9, when strain-rate, ė , is in s −1 , stress, σ, is in MPa and grain-size, d is in µm. At higher stresses (25–250 MPa) A = 100, H = 190 kJ mol −1 , n = 3.3 and m = −1.3. In the low stress regime, grains remain equidimensional during flow, a pre-existing preferred crystallographic orientation produced during cold-pressing tends to weaken and grain-boundary sliding is important. At higher stresses, a grain flattening fabric develops, the pre-existing preferred crystallographic orientation pattern is preserved, and recovery-accommodated intracrystalline plastic flow is inferred to be the dominant deformation mechanism. Grain-size sensitivity of the flow stress persists even into the intracrystalline plastic flow regime. Grain-size insensitive flow only develops at grain-sizes greater than 40 µm, as demonstrated by reference to mechanical data for the flow of Carrara and Taiwan marbles. The flow laws which describe most of the experimental data do not extrapolate well through the lowest strain-rate data at the coarser grain-sizes. This indicates that a complete description of the flow, which can be used reliably to extrapolate to geological conditions, requires one or more of the material parameters A, n and m to be a function of one or more of stress, strain-rate and grain-size. This implies variable contributions from different deformation mechanisms as the deformation conditions change.

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

“…Walker et al [1990] observed the formation of voids in HT-HP deformation experiments on fine-grained synthetic calcite Comparison of a shear band (arrow) inspected with (e) crossed nicols and (f) transmitted light shows that the string-forming pore volume contains redistributed residual glass of the starting material (whitish spots in Figure 6f). Scale bars and experimental conditions are labeled at the bottom of each figure.…”

Deformation microstructures developed in the Iragawa mylonite zone in the western part of the Shirakami Mountains, Northeast Japan

“…uen, 1975;Passchier and Trouw, 2005;Kilian et al, 2011;Okudaira and Shigematsu, 2012 dislocation-accommodated grain boundary sliding DisGBS Walker et al, 1990;Rutter et al, 1994;Wang et al, 2010;Hansen et al, 2011 dynamic recrystallizationcontrolled dislocation creep DRX controlled creep Platt and Behr, 2011;Johanesen andPlatt, 2015 Walker et al, 1990;Rutter et al, 1994Wang et al, 2010Hansen et al, 2011 DisGBS Trouw, 2005 basal a rhomb a c LPO Lister, 1977;Schmid and Casey, 1986;, 1996 Y (Hirth et al, 2001) and grain boundary sliding (Gifkins, 1976), modified after Okudaira and Shigematsu (2012). The piezometric line is constructed after Stipp and Tullis (2003) with the correction given by Holyoke and Kronenberg (2010).…”

Towards an improved understanding of the mechanical properties and rheology of the lithosphere: an introductory article to ‘Rock Deformation from Field, Experiments and Theory: A Volume in Honour of Ernie Rutter’

“…Behrmann & Mainprice 1987;Brodie & Rutter 1987a, b), Walker et al (1990) provided the scientific community with the first deformation mechanism map (for calcite) showing an additional grain size-sensitive domain. This domain is characterized by a deformation mechanism that is transitional between dislocation creep and diffusion creep and, in calcite, has a stress exponent equal to 3 (Fig.…”

“…Brodie et al 1992;Khazanehdari et al 2000;Rutter et al 2007) and major fault zones (Chester & Logan 1986;Imber et al 2001;Faulkner et al 2003;Wibberley & Shimamoto 2003;; (2) the extrapolation of experimental constitutive equations for stable frictional sliding and quasi steady-state viscous flow to deformation in nature (e.g. Goetze & Evans 1979;Brace & Kohlstedt 1980;Carter & Tsenn 1987;Kohlstedt et al 1995); (3) the development of empirical and theoretical models that attempt to predict the conditions under which a particular rheology is likely to dominate and evolve (Walker et al 1990; e.g. Hirth & Kohlstedt 2003;Rutter & Brodie 2004a); (4) the study of earthquake depth distributions and gravity anomalies as proxies for continental strength (e.g.…”