Timing of Cenozoic Extension in the Southern Stillwater Range and Dixie Valley, Nevada. Issue 3 (21st March 2020)

• Record Type: Journal Article
• Authors: Colgan, J. P.; Johnstone, S. A.; Shuster, D. L.
• Is Part Of: Tectonics. Volume 39:Issue 3(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-03-21
• Subjects: Stillwater Range -- Dixie Valley -- Extensional faulting -- Thermochronology -- Inverse modeling; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2019TC005757
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: The Dixie Valley fault bounds the east side of the Stillwater Range in west‐central Nevada and last ruptured in 1954. Offset basalts indicate that slip began more recently than ~14 Ma, and prior work has interpreted the southern segment as an active low‐angle normal fault. Oligocene igneous rocks in the southern Stillwater Range were steeply tilted during large‐magnitude extension prior to ~14 Ma. To refine the timing of early extension and the onset of slip on the Dixie Valley fault, we collected two transects of samples for apatite fission track, apatite and zircon (U‐Th)/He (AHe and ZHe), and apatite 4 He/ 3 He thermochronometry. Apatite fission track ages from the Oligocene IXL pluton indicate rapid cooling ~18–14 Ma, and AHe and ZHe ages from the Cretaceous La Plata Canyon pluton indicate rapid cooling ~16–19 Ma. We interpret these data to record cooling during rapid extension. AHe ages from the IXL pluton are ~6–8 Ma and record cooling during slip on the Dixie Valley fault. We modeled these ages and 4 He/ 3 He spectra from one sample as the result of cooling during exhumation of a tilted fault block at a constant extension rate. The model predicts slip on the Dixie Valley fault beginning ~8 Ma. Although it does not constrain the initial fault dip, the model illustrates how a low‐angle fault requires a higher extension rate to reproduce cooling ages. Consequently, we prefer a high‐angle southern Dixie Valley fault for strain compatibility with the high‐angle northern segment. Key Points: Oligocene volcanic rocks in the southern Stillwater Range were tilted during Miocene (18–14 Ma) extension Slip on the Dixie Valley fault began ~8 Ma