Print this pageFault Related Alteration of Gouge in Sandstones
Jonathan Fry
Texas
A&M
University,
Department
of
Geology
&
Geophysics,
Center
for
Tectonophysics,
College
Station,
TX
USA
[email protected]
I
seek
to
establish
a
relationship
between
alteration
of
fault
gouge
and
seismic
displacement
of
the
host
fault.
The
fault
sample,
a
portion
of
the
San
Andreas
Fault
Observatory
at
Depth
(SAFOD)
Phase
One
core,
is
arkosic
sandstone
and
siltstone
separated
by
several
centimeters
of
fine-grain
gouge
material.
A
left-lateral
subsidiary
fault
of
the
San
Andreas
juxtaposes
the
two
rock
types
in
this
sample.
I
propose
that
thermochemical
and
mechanical
alterations
of
fault
gouge
record
the
micro-mechanisms
of
frictional
slip,
strength
characteristics,
and
slip-rate
history
(seismic
versus
aseismic)
of
the
fault.
Characterization
of
localized
chemical
changes,
microstructural
evidence
of
dissolution/precipitation,
mineral
alterations,
and
maturation
of
organic
particles
will
be
characterized
and
quantified.
Mechanical
and
fluid
flow
properties
of
the
fault
will
be
inferred
from
these
analyses.
Previous
work
in
fault
scaling
relationships
and
results
of
data
analysis
will
constrain
the
magnitude
of
frictional
heating
and
the
coefficient
of
sliding
friction.
Rotational
vitrinite
reflectance
measurements
of
dispersed
particles
within
the
gouge
will
be
analyzed
to
determine
mean
reflectance
(%Ro
mean)
and
orientation
of
max/min
reflectance.
Mean
reflectance
will
be
used
to
infer
maximum
temperature.
Orientation
of
%Ro
will
constrain
stress
anisotropy
during
maturation
and
differentiate
diagenetic
and
seismogenic
maturation
.
XRF
and
electron
microscopy
will
be
used
to
characterize
the
mineralogy
of
gouge
and
protoliths,
and
to
compare
structural
fabrics
to
experimentally
and
naturally
deformed
gouge
samples.
Preliminary
X-ray
fluorescence
(XRF)
data
show
distinct
chemical
boundaries
and
evidence
of
neoformed
minerals
corresponding
to
optically
observed
structural
domains
within
the
shear
zone.
AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects