Steady-State Microstructures of Quartz Revisited: Evaluation of Stress States in Deformation Experiments Using a Solid-Medium Apparatus

Katsuyoshi Michibayashi,Ichiko Shimizu

doi:10.3390/min12030329

Abstract

Dynamically recrystallizing quartz is believed to approach a steady-state microstructure, which reflects flow stress in dislocation creep. In a classic experimental study performed by Masuda and Fujimura in 1981 using a solid-medium deformation apparatus, two types of steady-state microstructures of quartz, denoted as S and P, were found under varying temperature and strain rate conditions. However, the differential stresses did not systematically change with the deformation conditions, and unexpectedly high flow stresses (over 700 MPa) were recorded on some experimental runs compared with the applied confining pressure (400 MPa). Internal friction in the sample assembly is a possible cause of reported high differential stresses. Using a pyrophyllite assembly similar to that used in the previous work and setting up paired load cells above and below the sample assembly, we quantified the frictional stress acting on the sample and corrected the axial stress. The internal friction changed in a complicated manner during pressurization, heating, and axial deformation at a constant strain rate. Our results suggest that Masuda and Fujimura overestimated the differential stress by about 200 MPa in their 800 °C runs. Crystallographic fabrics in the previous experimental sample indicated that the development of elongated quartz grains, which are characteristics of Type-S microstructures, was associated with preferential growth of unfavorably oriented grains during dynamic recrystallization.

Highlights

Since the discovery of hydrolytic weakening of quartz by D
Using an improved data acquisition system for a solid-medium apparatus, we simulated classical deformation experiments of agate conducted by MF and corrected the friction in the solid assembly
A relatively hard material of pyrophyllite was used for the confining medium, corrected flow stresses of wet quartz agreed well with those reported for wet quartz using gas-medium apparatus

Summary

Introduction

Since the discovery of hydrolytic weakening of quartz by D. T. Griggs in 1967 [1], solid-medium deformation apparatus have been utilized to simulate plastic deformation of quartz in the Earth’s crust, since high-pressure conditions, and high water fugacity conditions favorable for quartz deformation [2,3] can be relatively attained by compressing solid confining medium. Masuda and Fujimura [4] (hereafter referred to as MF) conducted axisymmetric compression tests on agate in wide ranges of temperatures (T = 700–1000 ◦ C) and strain rates (ε = 10−4 –10−6 s−1 ) at a confining pressure (Pc ) of 400 MPa using a solid-medium deformation apparatus developed by M. Kumazawa (hereafter referred to as Kumazawa apparatus) [5], as described below, and distinguished two types of quartz microstructures, denoted S and P, in recrystallized samples (Figure 1).

Methods

Results

Discussion

Conclusion