A prominent geophysical feature along the northern Nevada rift and its geologic implications, north-central Nevada

Abstract

We consider the origin and character of a prominent large-scale geophysical feature in north-central Nevada that is coincident with the western margin of the northern Nevada rift-a mid-Miocene rift that includes mafi c dike swarms and associated volcanic rocks expressed by a NNW-striking magnetic anomaly. The geophysical feature also correlates with mid-Miocene epithermal gold deposits and is coincident with the central part of the Battle Mountain-Eureka mineral trend. The Reese River Valley, a 2-km-deep Cenozoic basin, is located along the western margin of this feature and is inferred from the inversion of gravity data to be infl uenced by, and perhaps in part structurally controlled by, the geophysical feature. Geophysical modeling indicates that the source of the geophysical anomaly must extend to mid-crustal depths, perhaps refl ecting a transition from Paleozoic crust in the southwest to Precambrian crust in the northeast, the presence of felsic intrusive rocks in the middle crust, or the edge of mid-to subcrustal mafi c intrusions related to late Tertiary magmatic underplating associated with hotspot magmatism. These cases offer very different possibilities for the age, depth, and origin of the source of the geophysical anomaly, and they present distinct implications for crustal evolution in the northern Great Basin. For example, if the anomaly is due to a pre-Cenozoic basement structure, then its coincidence with the mid-Miocene northern Nevada rift suggests that the trend of the rift was guided by the preexisting crustal structure. On the other hand, if the anomaly is related to Tertiary mafi c intrusions, then the western limit of this mag-matism may have been infl uenced by hotspot fracturing of the crust.

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

“…Previous workers have suggested that the location and trend of the NNR may have been controlled by an existing crustal structure (e.g., Theodore et al, 1998;John et al, 2000;Ponce and Glen, 2008). This structure has been interpreted as a near-vertical crustal-scale fault parallel and adjacent to the NNR based on resistivity (Grauch et al, 2003) and gravity data (Ponce and Glen, 2008).…”

“…This structure has been interpreted as a near-vertical crustal-scale fault parallel and adjacent to the NNR based on resistivity (Grauch et al, 2003) and gravity data (Ponce and Glen, 2008). In the right circumstances, dikes can propagate along fractures that are not perpendicular to the least principal stress (e.g., Delaney et al, 1986), but NNR dikes do not appear to intrude preexisting faults where exposed in the fi eld and it is diffi cult to argue they record anything other than the least principal stress in the central part of the area shown in Figure 2 from ca.…”

Three-dimensional geologic model of the northern Nevada rift and the Beowawe geothermal system, north-central Nevada

“…There is a pronounced gravity gradient, increasing from west to east, at the western edge of the rift. This steep gradient is visible on all profi les to the south, except profi le EE', and likely refl ects the juxtaposition of dense basement rocks east of the eastern north-ern Nevada rift, with less dense basin deposits and basement rocks west of the rift (Ponce and Glen, 2008). In profi le EE', the gravity gradient is less pronounced because the eastern northern Nevada rift is juxtaposed against dense Paleozoic rocks on the west in the Shoshone Range, which decreases the density contrast.…”

“…Glen and Ponce (2002) describe several large-scale, NNW-trending, arcuate, mid-Miocene crustal structures in northern Nevada, including the eastern northern Nevada rift, which passes just west of the Beowawe geothermal system and is the focus of this study. The eastern northern Nevada rift has been divided into multiple segments from north to south based on interpretationof magnetic data (Zoback et al, 1994;Ponce and Glen, 2008). Zoback and Thompson (1978) and Glen and Ponce (2002) speculate the eastern northern Nevada rift and other associated rifts were localized along regional crustal fractures that were reactivated during emergence of the Yellowstone hotspot along the Oregon-Idaho border.…”

“…3) identifi ed by Zoback et al (1994) and . These segments may refl ect offsets along NEstriking, left-lateral faults (e.g., Mabey, 1966;Zoback et al, 1994), or they could refl ect primary en echelon emplacement of the eastern northern Nevada rift (Ponce and Glen, 2008).…”