The effect of different second-phase particle regimes on grain growth in two-phase aggregates: insights from in situ rock analogue experiments

Abstract

The aim of the study was to investigate the effect of rigid second phases on grain growth of a matrix phase. For this purpose, variable mixtures of norcamphor as the matrix phase, with glass beads (0.08-0.51 volume fraction) as second phase, were used to perform see-through rock-analogue experiments under static conditions at constant temperatures (50°C). Irrespective of the second-phase content, grain-size evolution of all mixtures can be subdivided into a stage of continuous grain growth, a transient stage and a stage of a finally stabilized grain size. On the grain-scale, the second phases affect the migrating grain boundaries either by pinning by single particles, by multiple particles or even by particle clusters. Summed up over the entire aggregate, these pinning regimes affect the average bulk grain size of the matrix grains, such that the changes in matrix grain size directly correlate with the amount of second phases, their dispersion and their degree of clustering. In this way, the matrix grain size decreases with increasing second-phase content, which can be expressed as a Zener relationship. Originating from the modification of an ordinary grain growth law, a new mathematical expression is defined, which allows the calculation of changes in the matrix grain size as a function of different second-phase volume fractions and particle sizes. Such models will be helpful in the future to predict microstructural changes in polymineralic rocks at depth.

Rock Strength and Texture Evolution During Deformation in the Earth's Ductile Lithosphere: A Two‐Phase Thermodynamics Model

“…Concerning the shapes of the grain‐size distributions, we assume self‐similar log‐normal grain‐size distributions (Rozel et al, ). This choice simplifies the mathematical treatment and remains reasonably consistent with natural observations in mono‐phase (Faul & Scott, ; Feltham, ; Slotemaker, ) and polyphase (Brodhag & Herwegh, ; Dimanov et al, ) aggregates. Rozel et al () proposes to account for the effect of self‐similar grain‐size distribution (variance normalized by the mean) on the prefactor of diffusion creep rheological law (see section and equation ).…”

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

“…The processes leading to a switch from dislocation creep to Newtonian flow remain ambiguous, as the microstructural record of such a transition is rarely observed in the field. Severe grain size reduction must occur to make diffusion creep effective, and usually requires metamorphic or fluid or melt present reactions (Brodie and Rutter, 1987;Dijkstra et al, 2002), resulting in fine-grained reaction products. Such a small grain size is rarely observed in monomineralic rocks, where grain size reduction processes always compete with grain growth processes during dynamic recrystallization (de Bresser et al, 2001).…”

Evolution of a polymineralic mantle shear zone and the role of second phases in the localization of deformation

“…The Zener parameter is defined as the size (d p ) divided by the volume fraction (f p ) of the second phases (d p /f p ; see Zener given by Smith [1948]). For polymineralic rocks with calcite as matrix mineral, the Zener trends have been extensively studied for static [ Berger and Herwegh , 2004; Berger et al , 2010; Brodhag and Herwegh , 2010] and for different deformation conditions (different temperatures and strain rates [e.g., Herwegh and Jenni , 2001; Herwegh et al , 2005; Ebert et al , 2007, 2008]). It proved to be a powerful approach, allowing the reconstruction of grain size evolution maps [ Herwegh et al , 2005] in which the dependence of the matrix grain size on the volume fraction, size, and distribution of second phases can be determined.…”