structural geology, propagation mechanics and - Stanford School of ...

There also are relatively high-angle tabular zones composed of multiple shear bands
(Flodin and Aydin, 2004). Abundant cross-cutting relationships consistently indicate that
shear banding represents a distinct phase of deformation subsequent to CB formation,
leaving CBs as the oldest structural fabric present (Hill, 1989; Taylor and Pollard, 2000;
Myers and Aydin, 2004; Flodin and Aydin, 2004; Eichhubl et al., 2004; Sternlof et al.,
2005). The highest density of low-angle shear banding occurs in close proximity to the
Summit-Willow Tank thrust and extends into the overlying Cretaceous units exposed
beneath it, suggesting a direct genetic relationship with emplacement of the thrust sheet
(Hill, 1989; Eichhubl et al., 2004; Sternlof et al., 2005). Compaction bands, on the other
hand, are restricted to the Aztec sandstone itself (Sternlof et al., 2005).
It appears that the Valley of Fire region was not affected by compression associated
with the early Tertiary Laramide orogeny (Bohannon, 1983), although it is possible that a
distributed tectonic fabric of joints may have formed during this time, when the study
area is interpreted to have been situated on the northeastern flank of a broad, gently
north-plunging arch (Bohannon, 1984). In any case, following some 40 million years of
relative tectonic quiescence, the next major event to impact the area was Basin and Range
extension beginning 15 to 20 Ma. This largely expressed itself as nested systems of both
left and right lateral strike-slip faults (generally with some dip slip) and associated
normal faults (Bohannon 1983, 1984; Burchfiel et al., 1992; Duebendorfer et al., 1998).
The major regional-scale features are the northeast-trending strands of the left-lateral
Lake Mead fault zone and the northwest-trending strands of the right-lateral Las Vegas
Valley shear zone (Figure 1.3). Associated structures developed within the Aztec
sandstone at the Valley of Fire include joints, sheared joints and a hierarchical network of
left-lateral and right-lateral joint-based strike-slip faults (Taylor et al., 1999; Myers and
Aydin, 2004; Flodin and Aydin, 2004). These Basin and Range related structures dissect
and to some degree obscure the CBs of interest, but the effects are generally local and not
difficult to account for.
Finally, the Aztec sandstone and overlying Cretaceous deposits in the central Valley
of Fire study area exhibit a very gentle, northeast-plunging synclinal fold (Figure 1.1)
referred to as the Overton syncline by Carpenter and Carpenter (1994) and attributed to
drag along the east-west trending, left-lateral oblique-slip Arrowhead fault, which bounds
18