The disposition of the clay mineral phases in activity-space, a generally major element conserved scatter of XRF data, and meteoric d18O ratios indicate that the environment of authigenesis was rock dominated. The lath-like grains define a weak to moderate preferred orientation, though with considerable discontinuity of planes across grain boundaries. The youngest authigenic products, such as MnO and rhodochrosite, create reaction halos documented by EDS compositional mapping. In other BSE images, however, similar reaction halos have been subjected to non-coaxial strain. Non-hydrostatic fluid pressures decrease the effective stress that a fault can sustain and clay mineralization is thought to lower friction, the two resulting in fault weakening and failure.
Compositional domains have distinct elemental composition and mineralogy.
Potential responses to, and the relative import of, these questions are discussed in the context of the data from the Death Valley detachments. Proceedings of Conference on Status of Geologic Research and Mapping in Death Valley National Park, Las Vegas, Nevada, April 9-11, 1999. We are investigating the origin and history of fault rocks developed along late Cenozoic and Quaternary low-angle normal faults at the western front of the Black Mountains. Fault rocks typically are disposed in regular zones beneath a sharp, striated fault plane. Fine-grained, locally flow banded gouge is present immediately beneath the fault plane.