structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
3.3. Deformation<br />
The Aztec also has been subjected to a varied <strong>and</strong> punctuated history <strong>of</strong> deformation<br />
driven by tectonic activity, starting with late Mesozoic compression <strong>of</strong> the Sevier<br />
Orogeny (e.g. Armstrong, 1968; Fleck, 1970; Brock <strong>and</strong> Engelder, 1977; Bohannon,<br />
1983) <strong>and</strong> jumping to Basin <strong>and</strong> Range extension beginning in Miocene time <strong>and</strong><br />
continuing to the present (e.g. Bohannon, 1983; Bohannon et al., 1993; Campagna <strong>and</strong><br />
Aydin, 1994; Flodin <strong>and</strong> Aydin, 2004; Myers <strong>and</strong> Aydin, 2004)). Figure 1.3 presents a<br />
generalized structure <strong>and</strong> tectonic map for the region, as compiled from multiple sources.<br />
Thin-skinned, east-vergent thrust faulting <strong>of</strong> the Sevier Orogeny may have initiated<br />
along the flanks <strong>of</strong> the exp<strong>and</strong>ing magmatic arc to the west <strong>of</strong> the study area during<br />
deposition <strong>of</strong> the Aztec, <strong>and</strong> progressively encroached on the Valley <strong>of</strong> Fire into latest<br />
Cretaceous time (Burchfiel et al., 1992). In general, Paleozoic carbonate rocks were<br />
placed atop Mesozoic clastic rocks along a piggy-backed sequence <strong>of</strong> low angle thrust<br />
ramps, each one accommodating up to tens <strong>of</strong> kilometers <strong>of</strong> shortening (Armstrong,<br />
1968). The easternmost extent <strong>of</strong> Sevier tectonism, at least ins<strong>of</strong>ar as expressed by<br />
exposed thrusts, reached just up to the Valley <strong>of</strong> Fire (Figure 1.3), first with the thin,<br />
short-traveled (kilometers) Summit-Willow Tank thrust, which placed lower Aztec atop<br />
upper Aztec <strong>and</strong> as much as 600 m <strong>of</strong> Cretaceous deposits, then with the kilometers thick,<br />
far-traveled (tens <strong>of</strong> kilometers) Muddy Mountain thrust, which placed Paleozoic<br />
carbonates over Aztec riding atop the Summit-Willow Tank thrust (Armstrong, 1968;<br />
Bohannon, 1983; Brock <strong>and</strong> Engelder, 1979; Carpenter <strong>and</strong> Carpenter, 1994; Longwell,<br />
1949). The preponderance <strong>of</strong> stratigraphic, <strong>structural</strong> <strong>and</strong> diagenetic evidence indicates<br />
that the Aztec s<strong>and</strong>stone now exposed in the main tourist part <strong>of</strong> the Valley <strong>of</strong> Fire State<br />
Park (the primary study area) was never buried by either thrust sheet, only by the upward-<br />
coarsening sequence <strong>of</strong> Cretaceous clastic deposits shed from them (Bohannon, 1984;<br />
Taylor, 1999; Eichhubl et al., 2004; Sternl<strong>of</strong> et al., 2005), which consist largely <strong>of</strong><br />
reworked Aztec s<strong>and</strong>stone (Bohannon, 1983).<br />
Structures formed in the Aztec s<strong>and</strong>stone that are associated with Sevier tectonism<br />
include the north-northwest trending, steeply east-dipping CBs that are the subject <strong>of</strong> this<br />
paper, <strong>and</strong> low-angle shear b<strong>and</strong>s that tend to parallel depositional bedding <strong>and</strong> exhibit a<br />
top-to-the-east sense <strong>of</strong> shear which mimics the large-scale thrust faults.<br />
16