Olivine friction at the base of oceanic seismogenic zones
Citable URI
https://hdl.handle.net/1912/1520As published
https://doi.org/10.1029/2006JB004301DOI
10.1029/2006JB004301Keyword
Olivine; Friction; Laboratory experimentsAbstract
We investigate the strength and frictional behavior of olivine aggregates
at temperatures and effective confining pressures similar to those at the base
of the seismogenic zone on a typical ridge transform fault. Triaxial compression
tests were conducted on dry olivine powder (grain size ≤ 60 μm) at effective
confining pressures between 50 and 300 MPa (using Argon as a pore
fluid), temperatures between 600°C and 1000°C, and axial displacement rates
from 0.06 to 60 μm/s (axial strain rates from 3 × 10−6 to 3 × 10−3 s−1).
Yielding shows a negative pressure dependence, consistent with predictions
for shear enhanced compaction and with the observation that samples exhibit
compaction during the initial stages of the experiments. A combination
of mechanical data and microstructural observations demonstrate that
deformation was accommodated by frictional processes. Sample strengths were
pressure-dependent and nearly independent of temperature. Localized shear
zones formed in initially homogeneous aggregates early in the experiments.
The frictional response to changes in loading rate is well described by rate
and state constitutive laws, with a transition from velocity-weakening to velocitystrengthening
at 1000°C. Microstructural observations and physical models
indicate that plastic yielding of asperities at high temperatures and low axial
strain rates stabilizes frictional sliding. Extrapolation of our experimental
data to geologic strain rates indicates that a transition from velocity weakening
to velocity strengthening occurs at approximately 600°C, consistent
with the focal depths of earthquakes in the oceanic lithosphere.
Description
Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): B01205, doi:10.1029/2006JB004301.
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