SOLUM, JOHN G., University of Michigan, Dept. of Geological Sciences, MI
ABSTRACT: Changes in Clay Mineralogy and Fabric Development Across Selected
Fault
Zones
Changes in clay mineralogy and the development of clay fabrics across
fault
zones provide information about the conditions that existed along faults when they
were active, which has implications for
fault
mechanics. Clay gouge is a common component
of
fault
cores in most tectonic settings, thus insight into faulting gained from this
study may reflect conditions that are common to many types of faults worldwide.
Changes in clay mineralogy, specifically the transformation of smectite to illite and changes in the polytypes of illite, are quantified using software modeling of X-ray diffraction spectra or equations that involve ratios of polytype-specific peaks to peaks that are shared by all polytypes.
The development of clay fabrics is evaluated using high-resolution X-ray texture
goniometry. The development of a preferred orientation is significant because it
contributes to anisotropy of fluid flow in fault
zones (with enhanced flow parallel to the
fault
) and because a well-developed fabric parallel to the
fault
may result in a lowered
coefficient of friction perhaps accounting for the weak behavior of some faults.
Sampled faults include the Moab and Hurricane normal faults as well as unnamed small
displacement normal faults and the Parowan Gap thrust fault
in Utah, a normal
fault
in
Nevada, and the right lateral Punchbowl
fault
in southern California.
AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid