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 mafic 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 influenced 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 reflecting 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 sub-crustal mafic 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 pre-existing crustal structure. On the other hand, if the anomaly is related to Tertiary mafic intrusions, then the western limit of this magmatism may have been influenced by hotspot fracturing of the crust.

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