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Amorphization of quartz by friction: Implication to silica‐gel lubrication of fault surfaces
Author(s) -
Nakamura Yu,
Muto Jun,
Nagahama Hiroyuki,
Shimizu Ichiko,
Miura Takashi,
Arakawa Ichiro
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl053228
Subject(s) - quartz , slip (aerodynamics) , materials science , lubrication , amorphous solid , raman spectroscopy , composite material , amorphous silica , fault (geology) , fourier transform infrared spectroscopy , mineralogy , analytical chemistry (journal) , geology , crystallography , optics , chemical engineering , chemistry , thermodynamics , engineering , seismology , physics , chromatography
To understand physico‐chemical processes at real contacts (asperities) on fault surfaces, we conducted pin‐on‐disk friction experiments at room temperature, using single crystalline quartz disks and quartz pins. Velocity weakening from friction coefficient μ ∼ 0.6 to 0.4 was observed under apparent normal stresses of 8–19 (18 > 19), when the slip rate was increased from 0.003 to 2.6 m/s. Frictional surfaces revealed ductile deformation of wear materials. The Raman spectra of frictional tracks showed blue shifts and broadening of quartz main bands, and appearance of new peaks at 490–520 and 610 cm −1 . All these features are indicative of pressure‐ and strain‐induced amorphization of quartz. The mapping analyses of Fourier transform infrared (FT‐IR) spectroscopy at room dry conditions suggest selective hydration of wear materials. It is possible that the strained Si‐O‐Si bridges in amorphous silica preferentially react with water to form silica‐gel. In natural fault systems, amorphous materials would be produced at real fault contacts and accumulate over the fault surfaces with displacements. Subsequent hydration would lead to significant reduction of fault strength during slip.