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Preliminary geologic map of the Herder Creek quadrangle, Elko County, Nevada [MAP AND TEXT]

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Title: Preliminary geologic map of the Herder Creek quadrangle, Elko County, Nevada

Author: Seth Dee and Michael W. Ressel
Year: 2016
Series: Open-File Report 16-5
Format: plate: 33 x 29 inches, color; text: 5 pages, b/w
Scale: 1:24,000

A 1:24,000-scale geologic map of the Herder Creek 7.5-minute quadrangle. The map area covers part of Starr Valley, the upper reaches of the Humboldt River, and the northwest part of the East Humboldt Range.

The Ruby Mountains–East Humboldt Range metamorphic core complex is exposed in the high-relief range front in the southeast part of the quadrangle. In this area, the core complex is comprised of intensely metamorphosed and highly attenuated Neoarchean through Mississippian(?) strata, thought to be part of the platform facies of the Proterozoic through Paleozoic passive margin. Contractional structures exposed in the map area are complex and difficult to discern due to overprinted extensional deformation but are likely part of the Winchell Lake nappe (WLN), a kilometer scale, southward-closing recumbent fold-nappe mapped in adjacent quadrangles to the east. Overturned Devonian to Neoproterozoic(?) meta-sedimentary strata exposed at the highest structural levels are interpreted to be in thrust contact with an underlying, upright sequence of Cambrian to Neoproterozoic(?) paragneiss and Paleoproterozoic to Neoarchean(?) orthogneiss in the core of the fold. This structural interpretation matches those from the adjacent Welcome quadrangle (McGrew and Snoke, 2015; NBMG Map 184). Rocks in the upper part of the metamorphic core complex are pervasively overprinted by a WNW-directed mylonitic shear fabric, which records middle to late Cenozoic extensional exhumation from mid-crustal depths. Abundant sills and lenses of less deformed Oligocene to Cretaceous garnet-muscovite leucogranite and biotite monzogranite intrude all metamorphic rocks in the quadrangle.

The west side of the East Humboldt Range is bound by the active, W-dipping Ruby Mountains frontal fault zone, which extends for more than 60 km to the southwest. A west step-over in the Ruby Mountains fault south of the Herder Creek drainage results in a broad, hanging wall uplift underlain by middle-Miocene to Pliocene strata comprised of NE-dipping to flat-lying tuffaceous sandstone, shale, and conglomerate of the Humboldt Formation and younger units. A tephra in the uppermost exposed section yielded a 40Ar/39Ar age on feldspar of 5.15 ± 1.82 Ma.

Repeated late Quaternary surface-rupturing earthquakes along active traces of the frontal fault are recorded by increased uplift and dissection of Quaternary surfaces as a function of relative age. Fault scarps in Holocene deposits have up to 2.5 m of vertical separation while glacial outwash deposits from the two most recent Pleistocene glacial advances have scarp heights ranging from 6 to 32 m. The upper reaches of several drainages have well-preserved glacial moraine deposits that record the Angel Lake and Lamoille glacial advances. Adjacent to the Humboldt River, in the northwest corner of the quadrangle, 3 sets of abandoned terrace surfaces are preserved, including a broad surface comprised of gravel-rich alluvium that was likely deposited during a period of increased discharge during the latest Pleistocene.

This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G15AC00240, 2016.

Suggested citation:
Dee, S., and Ressel, M.W., 2016, Preliminary geologic map of the Herder Creek quadrangle, Elko County, Nevada: Nevada Bureau of Mines and Geology Open-File Report 16-5, scale 1:24,000, 5 p.