Effects of chemical environment on dislocation creep of quartzite

<jats:p>The water‐related chemical parameter that affects dislocation creep in quartzite has been determined from variations in sample strength and microstructure with chemical environment in buffered deformation and hydrostatic annealing experiments. Samples were weld‐sealed in double capsules;<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0001.gif" xlink:title="equation image"/>, <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0002.gif" xlink:title="equation image"/>, <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> and <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0004.gif" xlink:title="equation image"/> were buffered using solid oxygen buffers, AgCl or CO<jats:sub>2</jats:sub>. Black Hills quartzite was deformed at 900°C and 1.5 × 10<jats:sup>−5</jats:sup>s<jats:sup>−1</jats:sup>. Two samples were deformed at ∼1700 MPa confining pressure at constant <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> and <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0004.gif" xlink:title="equation image"/>, with <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0001.gif" xlink:title="equation image"/> and <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0002.gif" xlink:title="equation image"/> varying over 8 and 15 orders of magnitude, respectively. Both samples deformed by climb‐accommodated dislocation creep with flow stresses of 300 MPa. Two additional samples were deformed at ∼700 MPa at constant <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> lower than for the 1700‐MPa samples, with <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0004.gif" xlink:title="equation image"/>varying over 2 orders of magnitude. Both samples faulted with a peak strength of ∼800 MPa. These four experiments suggest no dependence of dislocation creep strength on <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0001.gif" xlink:title="equation image"/>, <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0002.gif" xlink:title="equation image"/> or <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0004.gif" xlink:title="equation image"/>; instead, a strong dependence of strength on <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> is inferred. Previously deformed samples of Heavitree quartzite were hydrostatically annealed for 4 days at 800°C and 1200 or 500 MPa confining pressure, varying <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0004.gif" xlink:title="equation image"/> and <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> over 2.5 and 1 order of magnitude, respectively. The microstructures of these samples show increased rates of dislocation climb and grain boundary migration with increasing <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> but no dependence on <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0004.gif" xlink:title="equation image"/>. These buffered experiments indicate that dislocation creep is affected by <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> alone and suggest that the exponent for the <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb10663-math-0003.gif" xlink:title="equation image"/> term in the power law creep flow law is >2.</jats:p>