Kinematic evolution of a large-offset continental normal fault system, South Virgin Mountains, Nevada

Abstract

The South Virgin Mountains and Grand Wash trough comprise a mid-Miocene normal fault system that defines the boundary between the unextended Colorado Plateau to the east and highly extended crust of the central Basin and Range province to the west. In the upper 3 km of the crust, the system developed in subhorizontal cratonic strata in the foreland of the Cordilleran fold and thrust system. The rugged topography and lack of vegetation of the area afford exceptional three-dimensional exposures. Compact stratigraphy and well-defined prefaulting configuration of the rocks permitted a detailed reconstruction of the system. Reconstruction of cross sections based on more than 300 km 2 of detailed mapping at a scale of 1:12 000 shows that the fault system accommodated more than 15 km of roughly east-west-directed Miocene extension. Extension was initially accommodated on moderately to steeply dipping listric normal faults. As the early faults and fault blocks tilted, steeply to moderately dipping faults initiated within the fault blocks, soling into the early faults. Some of the early faults were active at dips of Ͻ20؇. Isostatically driven tilting is superimposed on tilting due to active slip and domino-style rotation of the fault blocks. Collectively these processes rotated originally steeply dipping faults to horizontal orientations. The kinematics are inconsistent with the widely accepted view that many near-horizontal normal faults were rotated to their present orientations by later, crosscutting normal faults. However, re

Cenozoic tectonic evolution of the central Wassuk Range, western Nevada, USA

“…This relationship is similar to that documented in the Singatse Range to the west (Proffett and Proffett, 1976;Proffett and Dilles, 1984). However, on the western margins of the Grey Hills, Buck Brush Spring, and Wassuk blocks, the second generation of faults is proximal to the surface exposure of the first generation of normal faults that accommodated most of the extension in the area, suggesting an intimate relationship between the first and second generations of faults, with the second generation of faults possibly transferring slip onto the lowangle first-generation fault surfaces at depth, merging with the older faults, similar to the interpretation of Brady et al (2000) for the Singatse Range to the west. In either case, the second generation of normal faults did not accommodate a significant percentage of the total extension documented in the field area.…”

“…The wider spacing of faults relative to the first generation (4 -6 km) appears to be influenced by the position of the first generation of faults (Figs. 3 and 7C), suggesting either a direct kinematic relationship (e.g., Brady et al, 2000) or a pre-existing zone of weakness in the upper most crust adjacent to the surface exposure of the first generation, permitting the downward propagation of faults and the establishment of the second generation of faults.…”

The anatomy of the 2009 L'Aquila normal fault system (central Italy) imaged by high resolution foreshock and aftershock locations

“…Such geometry is imaged for the first time by seismicity distribution. The fault is composed of planar segments with different dips along depth rather than a smoothly curving single fault surface [Brady et al, 2000;Rigo et al, 2004]. Resor et al [2005] proposed the same kinked geometry for the master listric fault responsible for the 1995 Kozani-Grevena (Greece) earthquake.…”

“…Thus, along the fault length, we observe fault segments with different dips and not round off as proposed by field geologist describing listric geometry [e.g., Brady et al, 2000].…”

Observations from the Basin and Range Province (western United States) pertinent to the interpretation of regional detachment faults

“…Armstrong 1972;Crittenden et al 1980;Wernicke 1981Wernicke , 1985Allmendinger et al 1983;Davis 1983;Miller et al 1983;Spencer 1984;Lister & Davis 1989;Spencer & Chase 1989;Axen et al 1990Axen et al , 1993John & Foster 1993;Livaccari et al 1993;Axen & Bartley 1997;Brady et al 2000a;Snow & Wernicke 2000;Livaccari & Geissman 2001;Axen 2004;Carney & Janecke 2005). The detachment concept is now widely applied in extensional and passive margin settings (e.g.…”