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