Experimental Control of the Water-Weakening Effect in Quartz

  1. B.E. Hobbs and
  2. H.C. Heard
  1. A. Ord and
  2. B. E. Hobbs

Published Online: 18 MAR 2013

DOI: 10.1029/GM036p0051

Mineral and Rock Deformation: Laboratory Studies: The Paterson Volume

Mineral and Rock Deformation: Laboratory Studies: The Paterson Volume

How to Cite

Ord, A. and Hobbs, B. E. (1986) Experimental Control of the Water-Weakening Effect in Quartz, in Mineral and Rock Deformation: Laboratory Studies: The Paterson Volume (eds B.E. Hobbs and H.C. Heard), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM036p0051

Author Information

  1. Department of Earth Sciences, Monash University, Australia

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1986

ISBN Information

Print ISBN: 9780875900629

Online ISBN: 9781118664353

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Keywords:

  • Rocks—Testing—Addresses, essays, lectures;
  • Rock deformation—Addresses, essays, lectures

Summary

Experiments have been conducted to investigate the influence of the fugacity of oxygen, fO2, upon the strength of single crystals of natural quartz, loaded in the l m orientation, and deformed in the presence of H2O vapor. The conditions for these experiments are 800°C, 1.64 GPa confining pressure, and a strain-rate of 10−5s−1. Solid oxygen buffers were used to produce fO2 in the range 2.19×10−31 MPa to 2.60×10−3 MPa corresponding to a range in fH2O of 6.08×10−2 MPa to 6. 93×10−3 MPa and a range in fH2O of 2.61×104 MPa to 2.73×10−5 MPa. Specimens deformed under differing conditions of fH2O and of fO2 display a complete spectrum of mechanical behavior ranging from strong (σ ≈ 1500 MPa) at low fH2O and low fO2 to weak (σ ≈ 200 MPa) at high fH2O and high fO2. Under conditions where fH2O is kept constant and only fO2 varies, the strength at constant strain-rate decreases with increase in fO2. Preliminary creep data also indicate that both the strain-rate and the dynamically recrystallized grain size are functions of both fH2O and fO2 at constant stress, temperature, and pressure. All of these specimens show “broad-band” infrared absorption; it appears that the (OH)-concentration due to hydrogen interstitials remains fairly constant with increase in fO2 whereas the “broad band” absorption increases with increase in fO2. Although these data are preliminary much of the behavior may be explained by either of the two neutrality ranges $$[{\rm H}ˆ{\rm i}ˆ \bullet ]\, = \,2[{\rm O}ˆ{\rm p}ˆ{\rm } ]$$ where Op is the peroxy defect or $$[{\rm H}ˆ{\rm i}ˆ \bullet ]\, = \,4[{\rm V}ˆ{{\rm Si}}ˆ{} ]$$. Within the first neutrality range the observed creep rates are consistent with a deformation mechanism in which diffusion of $${\rm O}ˆ{\rm p}ˆ{\rm } \,{\rm or}\,{\rm H}ˆ{\rm i}ˆ \bullet$$ or of the two defects together is rate controlling. Such a process is identical to that postulated by Griggs and Blacic [1965] . Within the second neutrality range the observed creep rates are consistent with a deformation mechanism in which diffusion of $${\rm V}ˆ{{\rm Si}}ˆ{{\rm }}$$, presumably coupled with diffusion of $${\rm H}ˆ{\rm i}ˆ{\rm - }$$, is rate controlling. The experimental data cannot distinguish between these two possibilities. The observed solubility of (OH) in quartz under these conditions is more consistent with the defect being incorporated as $${\rm H}ˆ{\rm i}ˆ \bullet$$ and/or $$(2{\rm H}ˆ{\rm i}ˆ \bullet \, + \,{\rm O}ˆ{\rm p}ˆ{\rm } )$$ rather than as (4H)Si or (3H)si.