An Experimental Study of the Role of Water in Quartz Deformation

Abstract

Basic equilibrium and kinetic properties of water in quartz are elucidated in a combined mechanical, infrared absorption, and electron microscope study on a hydroxylbearing synthetic quartz crystal. Changes in yield strength and nature of infrared absorption observed after heating specimens at 900øC and various pressures are correlated with the precipitation or redissolution of water in bubbles visible in the electron microscope. From these observations it is concluded that the solubility of water in quartz at 900øC and 300 MPa pressure is between 200 and 400 H per 106Si and that the diffusivity of the dissolved hydroxyl-bearing species is very low, probably less than 10 -•9 m •' s -• at 900øC in initially dry quartz but increasing significantly with hydroxyl concentration. These results explain the sluggishness and associated experimental difficulties in studies on hydrolytic weakening in this pressure range. They indicate that equilibrium may not be attained in many such experiments and pose pertinent questions concerning extrapolation to geological conditions. 49 MPa) is an important factor. A similar conclusion follows from observations of lower strength in quartzite at higher pressures by Tullis et al. [1979]. The reasons for the pressure effect have not yet been elucidated, but pressure is clearly an important variable.The present study, combining mechanical, infrared absorption, and electron microscope approaches, attempts to separate and to identify some basic equilibrium and kinetic aspects of the role of OH in the properties of quartz. Preliminary accounts of the findings have been given in Kekulawala et al. [1978] and in Paterson and Kekulawala [1979]. The latter paper also gives a review setting out the background in some detail, which therefore need not be repeated here. We shall now describe observations on the mechanical properties of synthetic quartz crystals subjected to various histories of heat treatment and relate these observations to infrared absorption spectra measured at low temperature and to electron microscope observations on bubbles. The observations will then be discussed in terms of the solubility and diffusivity of the kinetically effective hydroxyl species responsible for hydrolytic weakening. Finally, some implications for the mechanical properties of quartz under other conditions are considered. Apparatus and ProceduresDeformation tests were carried out in an argon gas-medium high pressure apparatus, previously described [Pa- terson, 1970]. The apparatus has an internal furnace and an internal load cell. Displacements are determined with an externally mounted LVDT, correcting for apparatus

Water redistribution in experimentally deformed natural milky quartz single crystals—Implications for H2O‐weakening processes

“…This interpretation is consistent with results by Kronenberg et al []: After heating a dry natural quartz crystal in talc for 11 h, the material is weak (from infiltration of H 2 O through cracks), as found by Griggs and Blacic [], but after heating it for 112 h, the material is substantially stronger (because the fluid inclusions have grown in size). This behavior is well known for synthetic quartz, where fluid inclusion growth after annealing hardens the material and produces freezable water [ Kekulawala et al, ]. Thus, during heating in talc, very small fluid inclusions and defects will be formed from microcracking (inducing H 2 O weakening in such crystals), but if these inclusions grow, their weakening effect by dislocation generation decreases.…”

“…The rounded and the pointed absorption band observed here are both referred to as “broad absorption band” in the literature without making a systematic distinction between them [ Aines and Rossman , ; Rovetta , ; Kronenberg , ]. The type of broad absorption band which we have termed “rounded broadband” has been observed in different types of quartz and is assigned to molecular water in clusters or inclusions or grain boundaries [ Kekulawala et al, ; Kronenberg and Wolf , ; Kronenberg , ].…”

“…H 2 O weakening of quartz is associated with molecular forms of H 2 O and/or with dissociated forms of H 2 O present as a hydrogarnet (4H)Si or other isolated (OH) and/or structurally bound defects [ Doukhan and Trépied , ; Paterson , ; Kronenberg , ; Cordier et al, ]. Molecular H 2 O may form small fluid clusters in synthetic quartz [ Kekulawala et al, ; Paterson , ; McLaren et al, ] or fluid inclusions in natural quartz. Very small aggregates of H 2 O (<1 to a few nm) are referred to as clusters (up to ~200 molecules of H 2 O [ Aines et al ., ]).…”

“…However, it has been noticed from the beginning of experimental work that the distribution of strain is inhomogeneous in natural quartz [ Griggs , ; Blacic , ]. The problem was avoided by using synthetic crystals with a known and homogeneous H 2 O content (on the sample scale) in most subsequent experiments [ Blacic , ; Kirby , ; Morrison‐Smith et al, ; Kekulawala et al, ; Linker and Kirby , ; Doukhan and Trépied , ; Cordier and Doukhan , ; Cordier et al, ; Muto et al, ]. Morrison‐Smith et al [] have observed high dislocation densities and tangles in association with H 2 O clusters or minute fluid inclusions in synthetic quartz crystals.…”

Synchrotron FTIR imaging of OH in quartz mylonites

“…IR spectroscopy has been an important tool for studying OH defects in nominally anhydrous minerals and, in coordination with deformation experiments, to study the effects of water and hydrogen defects on mechanical properties (e.g., Kats, 1962;Griggs and Blacic, 1965;Kekulawala et al, 1978Kekulawala et al, , 1981Cordier and Doukhan, 1991;Mackwell and Kohlstedt, 1991;Bai and Kohlstedt, 1996;Kohlstedt et al, 1996). With the introduction of efficient FTIR spectrometers and IR microscopes, studies of intragranular water and hydrogen defects in naturally deformed rocks have been enabled using apertures of 50-100 µm Nakashima et al, 1995;Gleason and DeSisto, 2008;Finch et al, 2016;Kilian et al, 2016) as well as FTIR mapping of OH contents (Seaman et al, 2013).…”