New USGS Professional Paper 1832 – Eruptive History, Geochronology, and Post-Eruption Structural Evolution of the Late Eocene Hall Creek Caldera, Toiyabe Range, Nevada
Authors: Joseph P. Colgan[usgs.gov] (USGS) and Christopher D. Henry (NBMG)
Series: U.S. Geological Survey (USGS) Professional Paper 1832
Format: Report: viii, 43 p.; figure; data release
ISSN: 2330-7102 (online)
View/download here: https://pubs.er.usgs.gov/publication/pp1832[pubs.er.usgs.gov]
Abstract: The magmatic, tectonic, and topographic evolution of what is now the northern Great Basin remains controversial, notably the temporal and spatial relation between magmatism and extensional faulting. This controversy is exemplified in the northern Toiyabe Range of central Nevada, where previous geologic mapping suggested the presence of a caldera that sourced the late Eocene (34.0 mega-annum [Ma]) tuff of Hall Creek. This region was also inferred to be the locus of large-magnitude middle Tertiary extension (more than 100 percent strain) localized along the Bernd Canyon detachment fault, and to be the approximate location of a middle Tertiary paleodivide that separated east and west-draining paleovalleys. Geologic mapping, 40Ar/39Ar dating, and geochemical analyses document the geologic history and extent of the Hall Creek caldera, define the regional paleotopography at the time it formed, and clarify the timing and kinematics of post-caldera extensional faulting. During and after late Eocene volcanism, the northern Toiyabe Range was characterized by an east-west trending ridge in the area of present-day Mount Callaghan, probably localized along a Mesozoic anticline. Andesite lava flows erupted around 35–34 Ma ponded hundreds of meters thick in the erosional low areas surrounding this structural high, particularly in the Simpson Park Mountains. The Hall Creek caldera formed ca. 34.0 Ma during eruption of the approximately 400 cubic kilometers (km3) tuff of Hall Creek, a moderately crystal-rich rhyolite (71–77 percent SiO2) ash-flow tuff. Caldera collapse was piston-like with an intact floor block, and the caldera filled with thick (approximately 2,600 meters) intracaldera tuff and interbedded breccia lenses shed from the caldera walls. The most extensive exposed megabreccia deposits are concentrated on or close to the caldera floor in the southwestern part of the caldera. Both silicic and intermediate post-caldera lavas were locally erupted within 400 thousand years of the main eruption, and for the next approximately 10 million years sedimentary rocks and distal tuffs sourced from calderas farther west ponded in the caldera basin surrounding low areas nearby. Patterns of tuff deposition indicate that the area was characterized by east-west trending paleovalleys and ridges in the late Eocene and Oligocene, which permitted tuffs to disperse east-west but limited their north-south extent. Although a low-angle fault contact of limited extent separates Cambrian and Ordovician strata in the southwestern part of the study area, there is no evidence that this fault cuts overlying Tertiary rocks. Total extensional strain across the caldera is on the order of 15 percent, and there is no evidence for progressive tilting of 34–25 Ma rocks that would indicate protracted Eocene–Oligocene extension. The caldera appears to have been tilted as an intact block after 25 Ma, probably during the middle Miocene extensional faulting well documented to the north and south of the study area.
This publication was prepared in cooperation with the Nevada Bureau of Mines and Geology.
Authors: John L. Muntean and David A. Davis
Series: Open-File Report 2017-01
Version: supersedes Open-File Report 2014-01 (second edition)
Format: 31 x 34.5 inches, color
Scale: compilation at 1:1,000,000
View/download here: http://pubs.nbmg.unr.edu/NV-active-mines-and-energy-2017-p/of2017-01.htmSite locations and information on this map were obtained from a variety of published and non-published sources with the last updates made in January 2017. All sites shown on this map have had some form of production activity during 2016.
The map includes the names of the mining districts shown with a symbol marking the center of the district polygon—which does not necessarily represent the center of mining activity in that district. Mining district locations are taken from NBMG Report 47, Mining Districts of Nevada.
This map was prepared in cooperation with the Nevada Division of Minerals.
Preliminary Geologic Map of the South Half of the Mount Rose NW Quadrangle, Washoe County, Nevada
Authors: Nicholas H. Hinz and Alan R. Ramelli
Series: Open-File Report 16-6
Format: plate: 35 x 29 inches, color; text: 3 pages, b/w
This quadrangle straddles the north end of the Carson Range directly west-southwest of Reno and abuts the Nevada-California border. The Truckee River and Interstate 80 transect the northwest quarter of this quadrangle. This quadrangle also encompasses part of the rural community along Thomas Creek in the southeast quarter, and segments of the Steamboat irrigation ditch and part of the City of Reno urban area fall within the northeast corner.
The bedrock exposures in the quadrangle consist of Mesozoic granitic basement and Tertiary volcanic and sedimentary rocks. The Tertiary section includes a complex section of lavas, intrusions, and volcanic sedimentary rocks. Many of these volcanic and sedimentary rocks were derived from a ~6-7 Ma ancestral Cascades volcanic center in the Mount Rose quadrangle, directly south of this quadrangle. Plio-Pleistocene basaltic andesite lavas and rhyolite domes locally rest on the late Miocene volcanic rocks in the middle part of the quadrangle. Principal surficial deposits include late Pliocene to modern alluvial fan and fluvial deposits, Quaternary glacial deposits, and late Quaternary mass wasting deposits. Notable deep-seated landslide complexes reside in all major drainages—including Thomas Creek, Hunter Creek, Bronco Creek, and the smaller catchments along the west edge of the quadrangle. Most of the Carson Range is west-tilted with west-dipping Cenozoic strata. However, within the Mount Rose NW quadrangle, the dip domain flips and most all the Cenozoic strata dips east with numerous west-dipping normal faults. These west-dipping normal faults are cut by younger east-dipping normal faults of the Mount Rose fault zone on the east side of the range. East-facing Quaternary fault scarps were observed on the east side of the range and west-facing Quaternary fault scarps were observed on the west side of the range.
Preliminary Geologic Map of the Herder Creek Quadrangle, Elko County, Nevada
Author: Seth Dee and Michael W. Ressel
Series: Open-File Report 16-5
Format: plate: 33 x 29 inches, color; text: 5 pages, b/w
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.
Preliminary Geologic Map of the Boulder City Quadrangle, Clark County, Nevada
Authors: Seth Dee, Nicholas H. Hinz, R. Ernie Anderson, and Racheal Johnsen
Series: Open-File Report 16-4
Format: plate: 39 x 29 inches, color; text: 6 pages, some color
A 1:24,000 scale preliminary geologic map of the Boulder City 7.5-minute quadrangle in Clark County, Nevada. This quadrangle covers portions of the southeastern River Mountains, the northern Eldorado Mountains and straddles a segment of the drainage divide between the hydrologically closed Eldorado Valley and the through-flowing Colorado River Basin. Boulder City is located in the northern part of the quadrangle, as is the in-progress Interstate 11, Boulder City Bypass. This publication includes a combination of new mapping and integration with existing mapping by Ernie Anderson.
The bedrock exposures in the quadrangle are dominated by Tertiary plutonic, volcanic, and sedimentary rocks with lesser Proterozoic metamorphic rocks and Paleozoic sedimentary rocks. In the northern Eldorado Mountains the basal volcanic section includes the early to middle Miocene, intermediate to felsic composition Patsy Mine volcanics. The Patsy Mine volcanics are locally intruded by the composite, middle Miocene Boulder City pluton. This pluton is variably hydrothermally altered with actinolite present in altered groundmass and fracture-fill veins. Both the Boulder City pluton and the Patsy Mine volcanics are locally overlain by the middle Miocene Mount Davis volcanics which consist of a syn-extensional, bimodal sequence of lavas and tuffaceous sediments. In the southeastern River Mountains, the Tertiary strata are dominated by the middle Miocene, intermediate to felsic composition Red Mountain volcanics. These rocks are intruded by a middle Miocene granitic stock, which is probably related to widespread hydrothermal alteration of the Red Mountain volcanics. Locally overlying the Red Mountain volcanics are the less altered, intermediate to silicic, volcanics of Bootleg Wash, and unaltered Mount Davis volcanics.
The bedrock in the northern Eldorado Mountains is faulted by numerous north-striking, down-to-east and down-to-west normal faults. The northeast-striking, sinistral Hemenway Wash fault transects the northwest quarter of the quadrangle, separating the Eldorado Mountains from the River Mountains. The Hemenway Wash fault is one of the faults that makes up the >100 km-long, Lake Mead Fault System. In the northernmost Eldorado Mountains, fault strikes curve from N-S to NW and to E-W as they approach the Hemenway Wash fault zone, possibly due to oroclinal flexure. Provisional analysis of new geochronologic and geochemical data acquired in this study indicate that the plutonic and volcanic strata exposed in the southeastern River Mountains may correlate directly to strata in the northern Eldorado Mountain, providing a means to evaluate a range of possible displacements across the Hemenway Wash fault.
Surficial sediments in the quadrangle are largely alluvial fan and pediment deposits ranging from historic to Pliocene in age. Early Pleistocene to late Pliocene surficial deposits are characterized by 2+ m thick pedogenic carbonate horizons, which form resistant geomorphic surfaces on the east side of the Eldorado basin and cap many of the bedrock highlands in the Eldorado range. Fan deposits eroded from altered Boulder City plutonic rocks or from Miocene basin sediments may contain redistributed actinolite-bearing clasts. One possible fault scarp was observed in a late to middle Pleistocene aged fan. No other evidence for Quaternary faulting was recognized in the quadrangle.
Preliminary Geologic Map of the Apex Quadrangle, Clark County, Nevada
Author: Robert G. Bohannon
Series: Open-File Report 16-3
Format: plate: 31 x 32 inches, color; text: 5 pages, color
The Apex quadrangle (1:24,000 scale) is centered approximately 22.5 km northeast of downtown Las Vegas in Clark County, Nevada. Rocks in the quadrangle are exclusively sedimentary and include a mostly conformable sequence of Paleozoic continental shelf and platform rocks in its north half. The south half of the quadrangle is mostly Miocene interior-continental-basin deposits. Dissected alluvial deposits of Quaternary and latest Tertiary age, only the oldest of which are consolidated, discontinuously cover large lowland parts of the quadrangle. The Paleozoic rocks are deformed and in some places overturned by Mesozoic thrust faults associated with the Late Cretaceous Sevier Orogenic disturbance. A large east-vergent thrust fault with a northeast orientation, the Dry Lake Thrust, cuts the eastern half of the quadrangle, where it is mostly concealed by post-Cretaceous deposits. The thrust juxtaposes lower Paleozoic shelf rocks in the hanging wall above upper Paleozoic continental platform rocks in the footwall. Tertiary normal faults are also common and are mostly oriented northeast where they cut Paleozoic rocks. The Miocene beds, most of which post-date the northeast normal faults, are deformed by a few east-west or east-northeast-oriented faults and numerous small folds that are associated with them. The younger faults might be associated with very late-stage movement on the Las Vegas Valley shear zone which projects into the quadrangle from beneath Las Vegas Valley to the east, but the shear zone is otherwise concealed by the Miocene deposits.
The Publication Sales and Information Office at Great Basin Science Sample and Records Library will be closed the week of December 26–30, 2016.
No orders will be filled during this time period. If you will need any publications before January 3, 2017, please place those orders by December 20 to give us time to fill them before the week that we are closed.
We will be open our normal hours again on Tuesday January 3, 2017. We apologize for this inconvenience.
A River Runs through It—Geology along the Truckee River Valley from Reno to Pyramid Lake
Authors: Rich D. Koehler, Andrew V. Zuza, and James E. Faulds
Series: Educational Series 59
Format: 19 pages, color
Major stops on this field trip include the following:
- A “young” one-million-year-old lava that flowed into the Truckee River Canyon
- Paleo–Lake Lahontan sediments from glacial times
- Several major earthquake faults
- Tufa mounds
- Fossil locality with 15-million-year-old leaf imprints
This field trip follows the route of the Truckee River canyon from Reno to its terminus at Pyramid Lake (figure 1). From Pyramid Lake, the trip then continues southwest across the Virginia Mountains and south through Warm Springs and Spanish Springs valleys back to Reno.
The Truckee River is sourced from Lake Tahoe at an elevation of 6,233 ft (1,900 m) in the Sierra Nevada and flows 121 miles (195 km) to its terminus at the southern end of Pyramid Lake at elevation 3,793 ft (1,156 m). The river’s drainage basin encompasses around 3,060 sq. mi. (7,925 km2) and gets its name from the Paiute chief, Truckee. The Truckee River is the main source for agriculture irrigation and residential water needs in the Reno region and is susceptible to extreme flooding, especially during heavy winter rain storms. As a result, the flow of the river is regulated by a series of dams east of Truckee, California, including Boca Reservoir, Stampede Reservoir, Prosser Creek Reservoir, and Martis Creek Reservoir. Water transmission flumes line the upper part of the river and are susceptible to damage from rock fall and strong ground shaking during local earthquakes.
Many historic floods have affected the Truckee Meadows (Reno basin) area, including major events in 1862, 1875, 1890, 1904, 1907, 1928, 1937, 1943, 1950, 1955, 1963, 1986, and 1997. The devastating “New Year’s flood” of 1997 caused over 450 million dollars in damage and closed downtown businesses for weeks (figure 2). This event was caused by a phenomena known as the “Pineapple Express” in which several warm storms from the Hawaiian Islands produced heavy rainfall in the Sierras, saturating and melting the snow pack and resulting in flows around 18,000 cfs.
The trip discusses historic flooding history, paleo–Lake Lahontan timing and stratigraphy, the connection of Pyramid Lake to Lake Lahontan, Neogene tectonics and paleovalley offsets, recent tectonics and earthquake hazards, and bedrock geology. At stop 6, there is an opportunity to hunt for macroscopic fossils preserved in 15-million-year-old diatomite.
NBMG coordinates annual geology field trips for the public during Earth Science Week. These field trips are fun, educational, family oriented, and always free. NBMG has been an active participant in Earth Science Week since it began in 1998.
Discover Nevada Geology with Experts from NBMG
You are invited to join experts at NBMG’s Great Basin Science Sample and Records Library for a day of lectures, displays, tours, and activities!
Click here for Open House flyer:
The Open House is hosted by the Nevada Bureau of Mines and Geology (NBMG) at the Great Basin Science Sample and Records Library (GBSSRL) at 2175 Raggio Parkway in Reno. It is an opportunity for the general public to discover Nevada geology and learn more about our dynamic landscapes and unique geology.
Nevada is richly endowed with natural resources and has more gold and geothermal resources than any other state, but our evolving landscapes also make Nevada prone to natural hazards, including earthquakes, floods, and landslides. The Nevada Bureau of Mines and Geology is the state’s geological survey and charged with assessing our mineral, geothermal, and oil-gas resources while also analyzing natural hazards to mitigate their effects. The GBSSRL houses vast collections of reports and rock and mineral specimens on Nevada’s geology, resources, and geologic hazards.
We welcome the public to our third annual open house on October 15 to learn more about our unique environment.
10:30 a.m. to 11:20 a.m.
Controversies Surrounding the Origin of the World’s Two Largest Gold Belts:
The Witwatersrand of South Africa and the Carlin Trend of Nevada
by Dr. John Muntean, NBMG Research Geologist and Director of the Ralph J. Roberts Center for Research in Economic Geology
11:30 a.m. to 12:20 p.m.
Geothermal Energy: So Hot Right Now
by Dr. Bridget Ayling, NBMG Research Geologist and Director of the Great Basin Center for Geothermal Energy
1:30 p.m. to 2:20 p.m.
Unravelling the Earthquake History along the Most Exciting Road in America:
Quaternary Faults and Paleoearthquakes in Central Nevada
by Dr. Rich Koehler, NBMG Research Geologist
2:30 p.m. to 3:20 p.m.
Earth‘s Flex and Flow in Nevada
by Dr. Bill Hammond, NBMG Research Geodesist
ONGOING ACTIVITIES FOR KIDS OF ALL AGES!
Learn to gold pan
Tour the sample library
Find faults on air photos
Pick up a free radon test kit
Adopt a pet rock
Play geology games—and win prizes
Bring a rock for free identification
Find hazards near your home, work, or school
View maps and equipment on display
Buy publications on special sale
FREE RADON TEST KITS AT OPEN HOUSE
Susan Howe, Program Director of the Nevada Radon Education Program, will be at the Open House and will be distributing free radon testing kits and information on radon.
- Radon is a naturally occurring radioactive gas that comes from the decay of uranium found naturally in rocks, soil and water.
- Radon can enter homes and accumulate to dangerous levels, raising the risk of lung cancer in their home.
- In Nevada, 25 percent of tested homes have elevated radon concentrations in excess of the Environmental Protection Agency action level.
- The Nevada Radon Education Program will be offering free radon test kits to attendees.
Nevada Radon Education Program:
NEVADA RADON POSTER CONTEST
There is still time for your children and neighbors (ages 9 to 14) to enter the Radon Poster Contest!
The deadline is October 31, 2016, but students can bring their poster entries with them to the Open House on Saturday to submit to Susan Howe.
For more information, please read details in these links below.
2017 Nevada Radon Poster Contest:
This contest is sponsored by the Nevada Radon Education Program and the Nevada Division of Public and Behavioral Health.
GOLD PANNING—NEW THIS YEAR!
Volunteers from GPAA will be at the Open House to offer free lessons in gold panning.
EARTH SCIENCE WEEK SALE AT OPEN HOUSE
The following items will be 20% off only for Open House visitors on October 15:
Nevada Geology Calendar 2017:
Lake Tahoe 3-D poster (50% off this item only):
The discount is available while supplies last and is not available for online or phone orders.