Three new geologic maps available
Geologic Map of the Flowery Peak Quadrangle, Storey and Lyon Counties, Nevada
by Stephen B. Castor, P. Kyle House, Donald M. Hudson, and Christopher D. Henry
The 1:24,000-scale geologic map of the Flowery Peak quadrangle is an extension of mapping published recently by the Nevada Bureau of Mines and Geology in the adjacent Virginia City quadrangle. The Flowery Peak quadrangle, southeast of Reno and east of Virginia City, includes part of the Comstock mining district, an important historic source of precious metals. More than 60 lithologic units were mapped in the Flowery Peak quadrangle. Twenty-six units are in the three major mid-Miocene intermediate magmatic groups defined in the Virginia City quadrangle. Extensive Quaternary sedimentary deposits include eighteen units exposed in the Carson River Plains in the southeast part of the Flowery Peak quadrangle. Minor amounts of mid-Miocene sedimentary rocks, early Miocene and Oligocene ash-flow tuffs, late Miocene basalt, and Quaternary rhyolitic rocks are present. Mesozoic metasedimentary and granitic rocks occur as well. Mapping of hydrothermal veins and associated alteration in the Flowery Peak quadrangle extends similar mapping in the Virginia City quadrangle. Twelve new 40Ar/39Ar ages determined for igneous rocks in the Flowery Peak quadrangle, along with chemical and mineralogic data, are reported in text that accompanies the map along with full unit descriptions.
This map was prepared as part of the STATEMAP component of the National Cooperative Geologic Mapping Program in cooperation with the U.S. Geological Survey.
This map supersedes Open-File Report 06-16.
Available on the Web:
Map 180, one 35×31.5-inch color map with 3 cross sections, scale 1:24,000; 24-page text, b/w; folded or rolled, $23.00 or $16.00 (map only)
Open-File Report 13-10
Preliminary Geologic Map of the Central Lake Range, Southern Fox Range, and Northern Terraced Hills, Emerson Pass Geothermal Area, Washoe County, Nevada
by Ryan B. Anderson, James E. Faulds, and Gregory M. Dering
Detailed geologic mapping and stratigraphic-structural analyses have elucidated the kinematics, stress state, and structural controls of a “blind” geothermal system in Emerson Pass on the Pyramid Lake Paiute Tribe Reservation, western Nevada. The Emerson Pass area resides near the boundary of the Basin and Range and Walker Lane provinces of northwestern Nevada, at the northeast end of Pyramid Lake. Strata of the surrounding Fox Range, Lake Range, and Terraced Hills are comprised of late Miocene to Pliocene sedimentary rocks and the middle Miocene Pyramid sequence volcanic rocks, all overlying Cretaceous intrusions and Triassic to Jurassic metasedimentary rocks.
The active geothermal system is expressed as a 2-m shallow temperature thermal anomaly (maximum ~60°C) that lies at the western edge of a broad left step at the northeast end of Pyramid Lake between the north- to north-northeast-striking, west-dipping, Fox and Lake Range normal faults. The 2-m temperature surveys have defined a north-south elongate thermal anomaly that resides on a north- to north-northeast-striking normal fault. Additionally, travertine mounds, chalcedonic silica veins, and silica-cemented Pleistocene lacustrine gravels in Emerson Pass indicate a robust geothermal system active at the surface in the recent past, likely the early Holocene. Structural complexity and spatial heterogeneities of the strain and stress field have developed in the step-over region, but kinematic data suggest a west-northwest-trending (~280° azimuth) extension direction. The geothermal system is likely hosted in Emerson Pass as a result of enhanced permeability generated by the intersection of two oppositely dipping, southward- terminating north- to north-northwest-striking (Fox Range fault) and north-northeast-striking normal faults.
This publication was prepared with support from the U.S. Department of Energy. We thank the Pyramid Lake Paiute Reservation for access to tribal lands and logistical support throughout the project.
Available on the Web:
Open-File Report 13-10, one color plate with 3 cross sections, 51.5×39 inches, scale 1:24,000; inset map, scale 1:8,000; 9-page text, b/w, $21.00
Open-File Report 13-11
Preliminary Geologic Map of the Southern Lake Range, Washoe County, Nevada
by Peter S. Drakos and James E. Faulds
The southern Lake Range is dominated by east-tilted Tertiary volcanic rocks cut by a system of west-dipping normal faults. The Tertiary strata include a thin veneer of Oligocene ash-flow tuff and an ~1 km thick section of middle Miocene (~16 to 13.2 Ma) volcanic rocks (the Pyramid sequence) composed of thick sequences of mafic lavas and minor intercalated dacite, ash-flow tuff, and conglomerate. The Tertiary rocks rest nonconformably on Mesozoic granitic-metamorphic basement. Quaternary alluvial fan and lacustrine deposits locally cover older units within the Lake Range and crop out extensively within and along the margins of the adjoining basins. These basins are complex, east-tilted half grabens, bounded by west-dipping range-front faults along the Lake Range and Nightingale Mountains, and cut by systems of intrabasinal west-dipping normal faults. Cumulative normal displacement on the west-dipping normal fault system in the southern Lake Range area includes ~3.5 to 5.4 km within and along the eastern margin of the Pyramid Lake basin and ~1.8 km within the southern Lake Range. Concordant dips of strata (~20-35°) throughout the Miocene and Oligocene sections indicate that major extension began after ~13 Ma. Significant ongoing transtension and multiple fault intersections in the vicinity of the southern Lake Range suggest that this region has relatively high geothermal potential.
This publication was supported by a grant from the National Science Foundation. Final editing and cartography was supported by an American Recovery and Reinvestment Act grant from the Department of Energy. We thank the Pyramid Lake Paiute Reservation for access to tribal lands and logistical support throughout the project.
Available on the Web:
Open-File Report 13-11, one color plate with cross section, 26.5×24 inches, scale 1:24,000; 5-page text, b/w, $16.00