Mechanical Amorphization of Synthetic Fault Gouges During Rotary‐Shear Friction Experiments at Subseismic to Seismic Slip Velocities

Although the effects of mechanical amorphization by fault motion on fault rocks have been investigated both in nature and experiments, the relationship between slip processes and the amount of amorphous materials produced remains unclear. We performed rotary‐shear friction experiments on synthetic q...

Full description

Saved in:
Bibliographic Details
Published in:Journal of geophysical research. Solid earth 2020-10, Vol.125 (10), p.n/a
Main Authors: Kaneki, S., Oohashi, K., Hirono, T., Noda, H.
Format: Article
Language:English
Subjects:
Amorphization
Amorphous materials
Clay minerals
Experiments
fault gouge
Fault lines
Friction
friction experiment
Geophysics
Kaolinite
Low temperature
mechanical amorphization
Mineralogy
Minerals
Pressurization
Quartz
Rock
Rocks
Room temperature
Rounding
Shear
Silica
Silicon dioxide
Slip velocity
Temperature
Ultrafines
Velocity
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Although the effects of mechanical amorphization by fault motion on fault rocks have been investigated both in nature and experiments, the relationship between slip processes and the amount of amorphous materials produced remains unclear. We performed rotary‐shear friction experiments on synthetic quartz and kaolinite gouges at room temperature, normal stresses of 1 or 3 MPa, slip velocities of 0.001 or 1 m s−1, and displacements of 1–101 m. X‐ray diffraction and microscopic observation data revealed that mechanical amorphization in both materials was accompanied by grain‐size reduction, particle rounding, and the formation of ultrafine particles. The amount of amorphous materials produced was strongly dependent on mineralogy and total frictional work regardless of slip velocity. Therefore, mechanical amorphization can occur during both coseismic and subseismic slip. Amorphization of ~7 wt% of quartz gouge required 30.33 MJ kg−1 of frictional work, whereas for kaolinite gouge, only 0.77 MJ kg−1 was required, which is consistent with observed preferential amorphization of clay minerals in faults. For kaolinite, up to 6% of frictional work can be used for mechanical amorphization, indicating its potential importance for faulting energetics. Because some kinds of amorphous phyllosilicates release water at lower temperature than crystalline, mechanical amorphization of fault rocks may influence thermochemical pressurization. Gradual weakening of quartz gouge at 0.001 m s−1 slip velocity suggested that
ISSN:2169-9313
2169-9356
DOI:10.1029/2020JB019956