Miocene extension in the East Range, Nevada: A two-stage history of normal faulting in the northern Basin and Range

Abstract

The East Range in northwestern Nevada is a large, east-tilted crustal block bounded by west-dipping normal faults. Detailed mapping of Tertiary stratigraphic units demonstrates a two-phase history of faulting and extension. The oldest sedimentary and volcanic rocks in the area record cumulative tilting of ~30°-45°E, whereas younger olivine basalt fl ows indicate only a 15°-20°E tilt since ca. 17-13 Ma. Cumulative fault slip during these two episodes caused a minimum of 40% extensional strain across the East Range, and Quaternary fault scarps and seismic activity indicate that fault motion has continued to the present day. Apatite fi ssion track and (U-Th)/ He data presented here show that faulting began in the East Range ca. 17-15 Ma, coeval with middle Miocene extension that occurred across much of the Basin and Range. This phase of extension occurred contemporaneously with middle Miocene volcanism related to the nearby northern Nevada rifts, suggesting a link between magmatism and extensional stresses in the crust that facilitated normal faulting in the East Range.Younger fault slip, although less well constrained, began after 10 Ma and is synchronous with the onset of low-magnitude extension in many parts of northwestern Nevada and eastern California. These fi ndings imply that, rather than migrating west across a discrete boundary, late Miocene extension in western Nevada is a distinct, younger period of faulting that is superimposed on the older, middle Miocene distribution of extended and unextended domains. The partitioning of such middle Miocene deformation may refl ect the infl uence of localized heterogeneities in crustal structure, whereas the more broadly distributed late Miocene extension may refl ect a stronger infl uence from regional plate boundary processes that began in the late Miocene.

Thermochronometrically constrained anatomy and evolution of a Miocene extensional accommodation zone and tilt domain boundary: The southern Wassuk Range, Nevada

“…Their tectonic interpretations invoke complex midcrustal flow processes to explain geometries which can arise simply from differential tilting of fault blocks in the WR and PGH. Furthermore, their interpretation of the timing of deformation is based solely on the 40 Ar/ 39 Ar age data of units which predate and do not constrain the timing of Neogene tilting and disregards data from a number of studies documenting the timing, accommodation, and geometry of Miocene E‐W extension via fault‐block rotation in the WR [e.g., Proffett , ; McIntyre , ; Dilles and Gans , ; Stockli et al ., ; Surpless et al ., ; Krugh , ; Gorynski , ] and throughout the Basin and Range [e.g., Stewart , ; Miller et al ., ; Stockli et al ., ; Colgan et al ., , ; Fosdick and Colgan , ; Tincher and Stockli , ]. Most importantly, after palinspastic reconstruction of the tilted WR fault blocks the thermochronologic data presented here agree very well with documented Cenozoic cooling events in the western Basin and Range.…”

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

“…Although extension immediately followed the eruption of these lavas, it is likely that the boundary conditions placed on the region by west-facing subduction were as important to the initiation of extension as the addition of heat to the middle and upper crust by rising magmas, based on the widespread initiation of extension ca. 19 -14 Ma throughout the Basin and Range Province (e.g., Miller et al, 1999;Stockli 1999;Colgan et al, 2008;Fosdick and Colgan, 2008;Gonsoir and Dilles, 2008). The chemistry of these Miocene andesites supports lesser crustal contamination than that experienced by earlier magmas, possibly indicating a thinner crust beneath the area relative to the Oligocene.…”

Multistage Cenozoic extension of the Albion–Raft River–Grouse Creek metamorphic core complex: Geochronologic and stratigraphic constraints

“…The onset of Basin and Range faulting is younger toward the borders of the province; rapid slip on faults began ca. 15-10 Ma in both the northwestern and northeastern parts of the province, including the region in and around the ARG metamorphic core complex (e.g., Wells et al, 2000;Egger et al, 2003Egger et al, , 2010Colgan and Metcalf, 2006;Colgan et al, 2007;Fosdick and Colgan, 2008).…”