Diachroneity of Basin and Range extension and Yellowstone hotspot volcanism in northwestern Nevada

Abstract

Some of the earliest volcanic rocks attributed to the Yellowstone hotspot erupted from the McDermitt caldera and related volcanic centers in northwestern Nevada at 17–15 Ma. At that time, extensional faulting was ongoing to the south in central Nevada, leading some to suggest that the nascent hotspot caused or facilitated middle Miocene Basin and Range extension. Regional geologic relationships indicate that the total magnitude of extension in northwestern Nevada is low compared to the amount documented in central Nevada and that extension was accommodated almost entirely by the widely spaced, high-angle normal-fault systems that formed the modern ranges. The Santa Rosa Range is the closest major range to the McDermitt caldera. It was tilted ∼15° east and uplifted as an intact crustal block by ∼8 km of slip along a west-dipping normal fault on the west side of the range. Apatite fission-track data from the Santa Rosa footwall block indicate that faulting and extension was ongoing ca. 7.5 Ma and began as early as 10 Ma. Data from the Pine Forest Range to the west indicate a similar 8–10 Ma age for extensional faulting. Basin and Range extension in northwestern Nevada is therefore significantly younger than 17–15 Ma hotspot volcanism. This timing argues against a direct link between the Yellowstone hotspot and the initiation of extension, casting additional doubt on the role of the hotspot in extension across the broader Basin and Range Province.