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How brucite may affect the frictional properties of serpentinite

2001; United States Department of the Interior; Linguagem: Inglês

10.3133/ofr01320

2332-4899

D. E. Moore, D. A. Lockner, Kintaro Iwata, Hisashi Tanaka, J. D. Byerlee,

Geological and Geochemical Analysis

The frictional strength of brucite gouge has been measured at hydrothermal conditions to 450°C. At room temperature, brucite has a coefficient of friction, μ ≈ 0.30, making it one of the weakest minerals identified to date. With increasing temperature at a constant effective normal stress, the coefficient of friction of brucite decreases to a minimum of μ ≈ 0.20 near 300°C, and μ ≈ 0.22–0.24 in the temperature range 350–450°C. Brucite has a sheeted crystal structure, and its low frictional strength may be attributed to the relatively weak bonds between the layers. In addition, the temperature dependence of μ to ≈300°C can be explained in terms of the anomalously large coefficient of thermal expansion of brucite, which will further weaken the interlayer bonds. Brucite is a common constituent of serpentinite, and at ≈300°C, where brucite is weakest, all the major serpentine minerals have μ ≥ 0.5. The maximum expected brucite content of a serpentinite is close to 20% by weight or volume. That amount of disseminated brucite will lower the coefficient of friction of serpentinite by ≤10–15% in the deeper parts of the seismogenic zone. However, the effect will be much greater if shear can be concentrated along brucite-lined slip surfaces in the serpentinite body.