Effect of water on the rheology of experimentally deformed quartzite

Open Access
Publisher Website
Google Scholar
Abstract
Empirical flow laws have been determined for Simpson quartzite samples deformed to mechanical steady state in the α‐quartz stability field using Griggs‐Blacic solid‐medium deformation apparatus. Experiments were conducted on samples both as received (“dry”) and with water added via the dehydration of a talc confining medium (“wet”). Best fits of the power law type yield a stress exponent of 2.72±0.19, an activation enthalpy of 134±32 kJ mol−1, and a preexponential constant of 1.16 [+1.15, −0.58] × 10−7 MPa−2.72 s−1 for the dry quartzite law; and are 2.61±0.15, 145±17 kJ mol−1, and 5.05 [±5.00] × 10−6 MPa−2.61 s−1 for the wet quartzite. The enhanced hydrolytic weakening of the wet experiments appears to affect the flow laws mostly in the preexponential constants, possibly as a defect concentration term that is higher in the wet than in the dry law. Over the range of experimental conditions (750°–900°C, 10−7 to 10−4 s−1, and 1.0–1.25 GPa confining pressure), dry specimens are 1.5–2.5 times stronger than wet samples deformed at the same conditions. The microstructures produced are analogous to those observed in many natural quartz tectonites. Recrystallization is well developed in the wet but not the dry specimens. At flow stresses below 500 MPa, microstructures indicative of recovery are well developed. A comparison of our creep activation enthalpies with those determined from diffusion experiments are consistent with deformation of wet Simpson quartzite that is limited by oxygen self‐diffusion. Inconsistencies between the present study and previous studies are probably the result of differences in sample material, sample treatment, and sample assemblies (chemical environment).