Fabric transitions in quartz via viscoplastic self-consistent modeling part I: Axial compression and simple shear under constant strain

Abstract

International audienceQuartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures, leading to the development of different types of crystallographic preferred orientation (CPO) patterns. In this contribution we present the results of an extensive modeling of quartz fabric transitions via a viscoplastic self-consistent (VPSC) approach. For that, we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems. We have performed these simulations in axial compression and simple shear regimes under constant Von Mises equivalent strain of 100% (γ = 1.73), assuming that the aggregates deformed exclusively by dislocation glide. Some of the predicted CPOs patterns are similar to those observed in naturally and experimentally deformed quartz. Nevertheless, some classical CPO patterns usually interpreted as result from dislocation glide (e.g. Y-maxima due to prism < a > slip) are clearly not developed in the simulated conditions. In addition we reported new potential preferred orientation patterns that might happen in high temperature conditions, both in axial compression and simple shear. We have demonstrated that CPOs generated under axial compression are usually stronger that those predicted under simple shear, due to the continuous rotation observed in the later simulations. The fabric strength depends essentially on the dominant active slip system, and normally the stronger CPOs result from dominant basal slip in < a >, followed by rhomb < a > and prism [c] slip, whereas prism < a > slip does not produce strong fabrics. The opening angle of quartz [0001] fabric used as a proxy of temperature seems to be reliable for deformation temperatures of ~ 400 °C, when the main slip systems have similar behaviors

The role of strain hardening in the transition from dislocation-mediated to frictional deformation of marbles within the Karakoram Fault Zone, NW India

“…For example, the slip systems of quartz are relatively well constrained and quartz slip system analysis is widely applied in studies of crustal deformation (e.g. Law et al, 1990;Lloyd et al, 1997;Morales et al, 2014). However, single crystals of quartz exhibit complex yield behaviour, with strength dependent not only on temperature but also strain rate and intragranular water content (Hobbs et al, 1972)…”

“…material, and environmental conditions, primarily temperature (e.g De Bresser and Spiers, 1997;Morales et al, 2014)…”

Are quartz LPOs predictably oriented with respect to the shear zone boundary?: A test from the Alpine Fault mylonites, New Zealand

“…This crystallographic arrangement of {m} poles near X is expressed by a dominance of blue and green colors on the Inverse Pole Figure (IPF) map of Figure b and by the IPF diagram of Figure c. Morales et al [] simulated such fabrics using self‐consistent viscoplastic (VPSC) theory in simple shear where basal‐<a> and rhomb‐<a> slip were made soft relative to prism‐<a> slip.…”

“…(IPF) map ofFigure 3band by the IPF diagram ofFigure 5c Morales et al [2014]. simulated such fabrics using self-consistent viscoplastic (VPSC) theory in simple shear where basal-<a> and rhomb-<a> slip were made soft relative to prism-<a> slip.The symmetry and shape of the quartz LPOs are similar regardless of quartz content.…”

Deformation conditions during syn-convergent extension along the Cordillera Blanca shear zone, Peru

“…However, transitions between dominant slip mechanisms inferred from quartz CPOs may also be affected by changes of strain rate and/or the activity of water within the shear zone ( Fig. 9; Mainprice and Paterson, 1984;Stipp et al, 2002b;Mancktelow and Pennacchioni, 2004;Law, 2014;Morales et al, 2014). Excluding the weak fabrics of samples CB13-57a and CB13-55a (384 and 430 m, respectively), quartz CPOs indicate predominant activity of prism <a> slip and rhomb <a> slip, which are consistent with dislocation creep in quartz at >400 °C (Schmid and Casey, 1986;Stipp et al, 2002aStipp et al, , 2002bStünitz et al, 2003).…”