Zircon and apatite (U-Th)/He evidence for Paleogene and Neogene extension in the Southern Snake Range, Nevada, USA

Despite decades of study, the timing, rates, and magnitude of extension in the Basin and Range are poorly quantified in some areas. This study integrates new zircon and apatite (U-Th)/He analyses (ZrnHe and ApHe) with published thermochronologic data to quantify these extensional parameters in the Southern Snake Range (SSR) of east-central Nevada. The new ZrnHe dates range from 40.7 +/- 4.9 Ma in the western SSR to 21.0 +/- 3.3 Ma near the present-day trace of the Southern Snake Range Decollement (SSRD), and the ApHe dates range from 15.1 +/- 2.4 Ma in the central SSR to 13.6 +/- 0.7 Ma closest to the SSRD trace. These new and previously published low-temperature thermochronologic cooling ages were inverted for the extensional history of the SSR using a Bayesian Monte Carlo method incorporating Pecube. The posterior extensional histories indicate three significant pulses of extension occurred during the Paleogene and Neogene: (1) similar to 50-45 to similar to 38 Ma (Eocene), (2) similar to 33-30 to similar to 23 Ma (Oligocene), and (3) similar to 23-20 to similar to 10-8 Ma (Miocene). Modeled rates of extension were low at <= 0.5 mm a(-1); however, more rapid rates possibly occurred during the Eocene and the Miocene based on posterior histories. Net cumulative extension from posterior histories is 19.8 to 34.9 km, with a mean of 29.7 km. About 10-18 km of extension occurred during the Eocene and Oligocene. Model results indicate no relationship between extension and magmatism in the SSR. Our new model results and interpretations also indicate extensional collapse of the Nevadaplano initiated prior to similar to 17 Ma.