Rapid middle Miocene extension and unroofing of the southern Ruby Mountains, Nevada

Abstract

Paleozoic rocks in the northern Ruby Mountains were metamorphosed during Mesozoic crustal shortening and Cenozoic magmatism, but equivalent strata in the southern Ruby Mountains were never buried deeper than stratigraphic depths prior to exhumation in the footwall of a west dipping brittle normal fault. In the southern Ruby Mountains, Miocene sedimentary rocks in the hanging wall of this fault date from 15.2 to 11.6 Ma and contain abundant detritus from the Paleozoic section. Apatite fission track and (U‐Th)/He samples of the Eocene Harrison Pass pluton record rapid cooling that peaked ca. 17–15 Ma, while apatite fission track data from Jurassic plutons east and west of the southern Ruby Mountains indicate near‐surface temperatures (<60°C) since the Cretaceous. We interpret these data to record rapid unroofing of the southern Ruby Mountains during slip on the west dipping brittle detachment between 17–16 and 10–12 Ma, followed by minor high‐angle faulting. We interpret published Oligocene to early Miocene K‐Ar biotite and zircon fission track dates from the Harrison Pass pluton to be partially reset rather than to directly record fault slip. Our new data, together with published data on the distribution and composition of Miocene basin fill, suggest that rapid middle Miocene slip took place on the west dipping brittle detachment that bounds the Ruby Mountains and East Humboldt Range for 150 km along strike. This fault was thus active during a period of rapid extension (ca. 17–15 to 12–10 Ma) documented widely across the northern Basin and Range Province.

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

“…It also was responsible for widespread exhumation of the metamorphic rocks in the Ruby-East Humboldt-Wood Hills core complex (e.g., Mueller and Snoke, 1993a;Camilleri and Chamberlain, 1997;Wallace et al, 2008;Colgan and Henry, 2009;Colgan et al, 2010;Lund Snee et al, 2016). In northeastern Nevada, this phase of extension took place from ca.…”

“…During this period of convergence, northeastern Nevada formed part of the hinterland of the Sevier fold and thrust belt and underwent Jurassic and Cretaceous thrust faulting, plutonism, metamorphism, and as much as ~30 km of tectonic burial of Paleozoic basement (e.g., Hodges et al, 1992;Camilleri and Chamberlain, 1997;McGrew et al, 2000;Hallett and Spear, 2014). Convergence was followed by protracted, multiphase extension beginning in the Late Cretaceous and continuing to the present (e.g., Snoke and Miller, 1988;Hodges et al, 1992;Mueller andSnoke, 1993a, 1993b;McGrew and Snee, 1994;Camilleri and Chamberlain, 1997;McGrew et al, 2000;Howard, 2003;Sullivan and Snoke, 2007;Colgan et al, 2010;Pape et al, 2016;Lund Snee et al, 2016). Extension ultimately culminated in the exhumation of once structurally buried, mid-crustal metamorphic rocks in the Ruby Mountains-East Humboldt-Wood Hills metamorphic core complex and the associated Pequop Mountains (Fig.…”

“…12 Ma precludes assessment of earlier extension (Andrews et al, 2008;Knott et al, 2016b). However, south of the Rogerson graben, albeit very distal to the track of the hotspot, significant extension between 16 and 10 Ma predating the Rogerson graben has been documented in the Ruby-East Humboldt metamorphic core complex and the adjacent Windermere Hills (e.g., Mueller et al, 1999;Colgan et al, 2010). …”

“…17-16 and 12-10 Ma was relatively rapid and locally large magnitude (e.g., Colgan and Henry, 2009), and was partially manifest by the exhumation of mid-crustal metamorphic rocks in the Ruby-East Humboldt-Wood Hills and the Albion-Raft River-Grouse Creek metamorphic core complexes ( Fig. 1B; e.g., Mueller andSnoke, 1993a, 1993b;Camilleri and Chamberlain, 1997;Wells et al, 2000;Egger et al, 2003;Colgan and Henry, 2009;Colgan et al, 2010;Konstantinou et al, 2012). Since ca.…”

The Tooth of Time: The North American Cordillera from Tanya Atwater to Karin Sigloch

“…The name comes from the Ruby Mountains of Nevada, where an iconic metamorphic 'core complex' was exhumed during middle Miocene extension (Colgan et al 2010), following abortive subduction of North American crust beneath Rubia (Hildebrand 2009). GSA Books Editor Pat Bickford (Syracuse University) accepted the manuscript after critical review.…”