The grain size(s) of Black Hills Quartzite deformed in the dislocation creep regime

Renée Heilbronner,Rüdiger Kilian

doi:10.5194/se-8-1071-2017

Abstract

Abstract. General shear experiments on Black Hills Quartzite (BHQ) deformed in the dislocation creep regimes 1 to 3 have been previously analyzed using the CIP method (Heilbronner and Tullis, 2002, 2006). They are reexamined using the higher spatial and orientational resolution of EBSD. Criteria for coherent segmentations based on c-axis orientation and on full crystallographic orientations are determined. Texture domains of preferred c-axis orientation (Y and B domains) are extracted and analyzed separately. Subdomains are recognized, and their shape and size are related to the kinematic framework and the original grains in the BHQ. Grain size analysis is carried out for all samples, high- and low-strain samples, and separately for a number of texture domains. When comparing the results to the recrystallized quartz piezometer of Stipp and Tullis (2003), it is found that grain sizes are consistently larger for a given flow stress. It is therefore suggested that the recrystallized grain size also depends on texture, grain-scale deformation intensity, and the kinematic framework (of axial vs. general shear experiments).

Highlights

Black Hills Quartzite (BHQ) has been used extensively in experimental rock deformation
For regime 1, the 2-D root mean square (RMS) and the 2-D mean never reach the value attained by the Lazy Grain Boundaries (LGB) segmentation (Fig. 7)
Expressed in terms of the 3-D mode, the grain size of the starting material is 101 μm, which is much larger than the recrystallized grain size (Fig. 4, inset)

Summary

Introduction

Black Hills Quartzite (BHQ) has been used extensively in experimental rock deformation. BHQ was used to determine the widely used recrystallized quartz grain size piezometer of Stipp and Tullis (2003). Among the microstructure analyses that were performed in those original papers, grain size was usually determined using CIP misorientation images. The CIP method (computer-integrated polarization microscopy; details in Heilbronner and Barrett, 2014) is only capable of detecting the c-axis orientation of optically uniaxial materials and is only capable of detecting grain boundaries between grains that differ in c-axis orientation. One of the puzzling results found by Heilbronner and Tullis (2006) was that the recrystallized grain size seemed to depend on the crystallographic preferred orientation of the grains within a domain. The grain size seemed to depend on the flow stress, and on the orientation of the c axis with respect to the kinematic framework. In principle it is possible that some grain boundaries were missed

Results

Discussion

Conclusion