Dating the detachment fault system of the Ruby Mountains, Nevada: Significance for the kinematics of low-angle normal faults

Abstract

[1] The mechanics of low-angle normal faulting and metamorphic core complexes continue to be a subject of debate. We investigate the conditions, timing, and kinematics of slip in the late, upper-crustal stages of core complex evolution of the Ruby Mountains detachment fault at the well-exposed Secret Pass locality with an X-ray diffraction (XRD) and Ar-Ar study of clay gouge samples from three separate faults, two from the low-angle detachment system and one from a high-angle normal fault that soles into the main detachment fault system. XRD analysis and modeling of XRD analysis show that authigenic illite-rich illite/ smectite (I/S) in gouge at Secret Pass is distinguishable from clay phases in hanging wall rocks because the I/S in the gouges contains only one-water layer as opposed to the more common two-water I/S phases found in both the hanging wall and footwall. Ar-Ar ages for the monomineralic one-water I/S found in the hanging wall high-angle fault, the main detachment, and a lowangle normal fault structurally above the main detachment are 11.6 ± 0.1 Ma, 12.3 ± 0.1 Ma, and <13.8 ± 0.2 Ma, respectively. The not-quite-flat Ar-Ar spectra indicate the gouge illites grew over some interval of time and not in discrete events. The nearly overlapping ages indicate that gouge formation and thus the last major period of activity on the detachment were at 11-13 Ma and were active coevally as part of a kinematically linked fault system with the main detachment active at dips <45°and possibly as low as 22°.Citation: Haines, S. H., and B. A. van der Pluijm (2010), Dating the detachment fault system of the Ruby Mountains, Nevada: Significance for the kinematics of low-angle normal faults, Tectonics, 29, TC4028,

Timing and conditions of brittle faulting on the Silltal-Brenner Fault Zone, Eastern Alps (Austria)

“…1 M ? 1M d ) versus apparent K-Ar age, Ar-Ar age, or e kt -1 (where k is the decay constant and t is time) can provide both the protolith (100 %) and authigenic (0 %) ages (Pevear 1999;Van der Pluijm et al 2001Ylagan et al 2002;Haines and van der Pluijm 2010;Solum et al 2010;Duvall et al 2011;Hnat and van der Pluijm 2014).…”

Middle Miocene to Holocene tectonics, basin evolution, and paleogeography along the southern margin of the Snake River Plain in the Knoll Mountain–Ruby–East Humboldt Range region, northeastern Nevada and south-central Idaho

“…For example, the dip angle of most faults bounding Knoll Mountain range from ~24° to 40° and remnants of the Ruby-East Humboldt detachment in the Wood Hills and East Humboldt Range dip only a few degrees to the west, but were likely rotated to a low-angle during extension (e.g., Mueller and Snoke, 1993a;Camilleri and Chamberlain, 1997;McGrew and Snoke, 2015). The Ruby-East Humboldt detachment in the northern Ruby Mountains is inferred to have an original dip between ~24° and 45° (Haines and van der Pluijm, 2010), and in contrast, Colgan et al (2010) inferred that the detachment initially formed with a dip of ~57°, but was rotated to a low angle due to isostatically induced footwall rebound. Collectively, these observations suggest that fault dip may have varied from low to high angle.…”

Integrating 40Ar–39Ar, 87Rb–87Sr and 147Sm–143Nd geochronology of authigenic illite to evaluate tectonic reactivation in an intraplate setting, central Australia

“…10a & b; Hall, 2013). The stepped appearance of age and Cl/K spectra is commonly seen in samples that are composed of multiple, potentially detrital, heterochemical grains of varying age and grain-size, which were not identifiable with XRD (Haines and Van de Pluijm, 2010;Villa, 2013;Villa and Hanchar, 2013). Following recoil, low temperature steps result from extraction of 39 Ar from the least-retentive authigenic grains followed by progressive release from more retentive detrital grains at higher temperatures (Verdel et al, 2012).…”

“…Ar dating of illites is also negatively affected by geochemical pitfalls such as excess 40 Ar and enhanced Ar mobility due to point defects and disagreement between consistent use of retention or total-gas ages (Dong et al, 1995;Haines and Van de Pluijm, 2010;Clauer et al, 2012;Verdel et al, 2012). As such, we suggest that future geochronological studies of hydrothermal illites utilise both Rb-Sr and 40 Ar- 39 Ar methods.…”