Reappraisal of the relationship between the northern Nevada rift and Miocene extension in the northern Basin and Range Province

Abstract

The northern Nevada rift is a prominent mafi c dike swarm and magnetic anomaly in north-central Nevada inferred to record the Middle Miocene (16.5-15.0 Ma) extension direction in the northern Basin and Range province in the western United States. From the 245°-250° rift direction, Basin and Range extension is inferred to have shifted 45° clockwise to a modern direction of 290°-300° during the late Miocene. The region surrounding the northern Nevada rift was actively extending while the rift formed, and these domains are all characterized by extension oriented 280°-300°. This direction is distinctly different from the rift direction and nearly identical to the modern Basin and Range direction. Although the rate, structural style, and distribution of Basin and Range extension appear to have undergone a signifi cant change in the late Miocene (ca. 10 Ma), the overall spreading direction does not. Middle Miocene extension was directed perpendicular to the axis of the thickest crust formed during Mesozoic shortening and this orientation may refl ect gravitational collapse of this thick crust. Orientation of northern Nevada rift dikes may refl ect a short-lived regional stress fi eld related to the onset of Yellowstone hotspot volcanism.

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

“…We interpret the evolution of these fault systems to be strongly influenced by regional Basin and Range extension because of three factors. (1) The north to north-northeast strike of the fault systems is consistent with west to west-northwest regional extension directions that have persisted in northeast Nevada since the initiation of Basin and Range extension (e.g., Colgan, 2013). (2) The Knoll-Ruby fault system overall appears to have a relatively consistent style and history along its >190 km length extending from very distal to proximal to the Bruneau-Jarbidge and Twin Falls eruptive centers along the track of the hotspot (Fig.…”

“…General extension directions established during this time included northeast-southwest extension in southeast Idaho and a broad zone of northwest-southeast extension in Nevada, the center of which contained a narrow zone of northeast-southwest extension along the northern Nevada rift ( Fig. 14B; e.g., Rodgers et al, 2002;Colgan, 2013). These general extension directions would persist to the present (Figs.…”

“…These general extension directions would persist to the present (Figs. 14B-14I) with the exception of the northern Nevada rift, which was only active from 17 to 15 Ma and is thought to be related to the initiation of the hotspot (e.g., Rodgers et al, 2002;Payne et al, 2012;Colgan, 2013).…”

Yellowstone plume trigger for Basin and Range extension, and coeval emplacement of the Nevada–Columbia Basin magmatic belt

“…This term leads to a false impression, however, because there is little evidence for signifi cant 17-15 Ma rifting or continental extension associated with the belt. The northern Nevada rift itself has been described as uncharacteristic of most intercontinental rift zones, in that it is dominated by magmatic rocks without signifi cant graben-fi lling clastic rocks, and with only minor documented extension (John et al, 2000;Colgan, 2013). Because the entire belt is more accurately defi ned as a zone of magmatic intrusion dominated by shallow dike swarms, midcrustal intrusions, linear vent systems, and localized calderas, we refer to it herein as the "Nevada-Columbia Basin magmatic belt.…”

“…They further suggested that a change in plate boundary conditions after 10 Ma rotated the extension direction by ~45° to 290°-300°, thus producing the northeast trend that defi nes the current Basin and Range structure and topography. This long-held view, however, has come into question as new data have become available from a variety of recent structural, stratigraphic, and thermochronologic investigations in northern Nevada, summarized in Colgan (2013). These studies show that the region surrounding the northern Nevada rift was actively extending as the rift formed, generating consistent NE-trending structures that refl ect an extension direction of 280°-300° (Colgan, 2013).…”