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The first report of water/hydrolytic weakening of silicate minerals was based on the observation that the strength of quartz decreases significantly in the presence of the water released from talc, the confining medium used in some of high-pressure experiments (Blacic and Griggs 1965). Subsequently, a number of researchers have studied this important phenomenon in several different minerals. Publications examining the influence of water or protons on the creep behavior of nominally anhydrous silicate minerals are listed in Table 1⇓. Initial studies treated the water-weakening phenomenon as an on-off process; that is, minerals and rocks are weak under hydrous conditions but strong under anhydrous conditions. Further investigations, however, demonstrated that the strengths of nominally anhydrous minerals (NAMs) and rocks decrease systematically with increasing hydrogen concentration (Kronenberg and Tullis 1984; Kohlstedt et al. 1995; Post et al. 1996; Mei and Kohlstedt 2000a,b; Karato and Jung 2003).
Two quite different approaches have been used in analyzing the effect of water or protons on the strength of nominally anhydrous silicate minerals. In the first model, a mechanism is envisioned in which water hydrolyzes strong Si-O bonds via the reaction Si-O-Si + H2O → Si-OH·OH-Si (Griggs 1967), thus the term water or hydrolytic weakening. As a result, the glide of dislocations becomes easier in wet quartz than in dry quartz since Si-O bonds do not need to be broken if water is present. In this case of water/hydrolytic weakening, the rate limiting step is the propagation of kinks along dislocations, which is facilitated by diffusion of HOH along dislocation cores. The resulting dislocation velocity is assumed to be proportional to the HOH concentration (Griggs 1974). In effect, this analysis implies …