Precambrian Rocks of the Hall Valley Area, Front Range, Colorado

Wahlstrom, Ernest E.; Kim, Nam Keun

doi:10.1130/0016-7606(1959)70[1217:prothv]2.0.co;2

Cited by 10 publications

(12 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Hornblendic gneisses are intimately associated with felsic gneisses as indicated in preceding paragraphs. In the central Front Range, most bodies of hornblendic rocks are small and amphibolitic, but moderately extensive bodies of hornblende gneisses are present in the Montezuma area (Levering, 1935;Wahlstrom and Kim, 1959). The gneisses of that area are finely banded and consist of various combinations of andesine, hornblende, diopside, quartz, biotite, and epidote.…”

Section: Felsic and Hornblendic Gneissesmentioning

confidence: 99%

Rock units of the Precambrian basement in Colorado

Tweto¹

1987

Professional Paper

View full text Add to dashboard Cite

The term Precambrian basement as used in this report applies to all rocks of Precambrian age. Basement rocks are exposed in many places in mountain uplifts in central and western Colorado, but are buried beneath younger rocks in more than 86 percent of the State. The exposed basement consists of variously metamorphosed layered rocks and of intrusive igneous rocks, in about equal proportions. The buried basement is of the same general character as the exposed basement except for the presence in southeastern Colorado of a unit of moderately metamorphosed sedimentary and volcanic rocks (Las Animas Formation) not known elsewhere.The Precambrian rocks are all of Proterozoic age except in a small area near the northwest corner of the State, where Archean rocks at the south margin of the Wyoming cratonic age province are present, mainly in the subsurface. As exposed at the Colorado-Utah border and westward, the Archean rocks consist of gneisses about 2,700 m.y. (million years) in age and of the Red Creek Quartzite. The Red Creek is not conclusively dated but is interpreted as-probably older than the 2,500-m.y. age boundary between the Archean and Proterozoic Eons. The Archean gneisses are mainly of granitic composition and igneous origin. They are exposed only in small fault blocks separated from the Red Creek by zones of quartz mylonite. The Red Creek Quartzite consists of at least 4 km (13,000 ft) of metaquartzite, kyanite-bearing quartz-muscovite schist, and minor marble, all extensively intruded by sills now metamorphosed to amphibolite. Faulting that occurred before and at various times after deposition of the Red Creek indicates recurrent tectonism at the border of the Archean Wyoming province.The oldest and most widespread of the Proterozoic rocks in Colorado are gneisses in a complex that constitutes part of the floor on which younger Precambrian sedimentary units rest and the matrix into which igneous rocks were intruded. The gneisses were derived from a heterogeneous sedimentary and volcanic protolith. They are metamorphosed in the upper or the lower amphibolite facies in most places in Colorado, but are of lower metamorphic rank in a few areas. They are divided broadly into biotitic varieties, largely metasedimentary, and felsic and hornblendic varieties, largely metavolcanic. These rock units occur both in large discrete bodies and intimately interlayered with one another. The principal species of biotitic gneiss is biotite-quartz-plagioclase gneiss, some of which contains sillimanite, garnet, or cordierite. Metaquartzite and marble or calc-silicate rocks occur locally in the biotitic gneisses. In the subsurface in eastern Colorado, a metaquartzite-mica schist facies is predominant. The felsic gneisses are quartzofeldspathic and are thought to have been derived principally from tuffs and subvolcanic sills. The hornblendic gneisses include both amphibolites of basaltic composition and more silicic varieties probably derived from epiclastic rocks and tuffs of intermediate composition. Metamorphism of the gneis...

show abstract

Section: Felsic and Hornblendic Gneissesmentioning

confidence: 99%

Rock units of the Precambrian basement in Colorado

Tweto¹

1987

Professional Paper

View full text Add to dashboard Cite

show abstract

“…These rocks can be subdivided on the basis of their origin into metasedimentary rocks and igneous rocks. Mineralogically equivalent units have been mapped and studied in considerable detail by Wells (1956, 1959), Sims and others (1963), Sims, Drake, and Tooker (1963), and Wahlstrom and Kim (1959) in the mineral belt north and south of the tunnel area.…”

Section: Precambrian Rocksmentioning

confidence: 99%

“…Previous work in the area of the Roberts Tunnel includes that by Lovering (1935) in the Montezuma district, by Lovering and Goddard (1950) in the Front Range, and by Wahlstrom and Kim (1959) in Hall valley. Summaries of the geology of the tunnel area have been published by Wahlstrom and Hornback (1962) and Warner and Robinson (1967).…”

Section: Introductionmentioning

confidence: 99%

General geology of the Harold D. Roberts Tunnel, Colorado

Robinson¹,

Warner²,

Wahlstrom³

1974

Professional Paper

View full text Add to dashboard Cite

The Roberts Tunnel transects a geologically complex area in the Front Range of the Colorado Rocky Mountains. The area includes Precambrian igneous and metasedimentary rocks, Paleozoic and Mesozoic sedimentary rocks, and Tertiary igneous rocks. The structural history includes folding and faulting during Precambrian time and the Laramide orogeny.The Precambrian rocks, which constitute about two-thirds of the area penetrated by the tunnel, consist of a sequence of metasedimentary rocks that were invaded by igneous rocks. The age relations among the metasedimentary rocks are still in doubt, owing to the complexity of the structure. These rocks are, from East Portal to West Portal, a sequence of amphibolite and related calc-silicate rocks, a migmatite unit, a microcline gneiss unit, a biotite gneiss and schist unit containing some amphibolite, a sillimanitic biotite gneiss and schist unit, and a hornblende gneiss unit.The Precambrian metasedimentary rocks were intruded by granite of Precambrian age. The older granite, which is similar to the Boulder Creek Granite of other areas in the Front Range, is believed to have been emplaced at about the time of the metamorphism and plastic deformation of the Precambrian sedimentary rocks. The younger granite, which is similar to the Silver Plume Granite of other areas in the Front Range, is believed to have been intruded during a period of cataclastic deformation. Pegmatite and aplite of Precambrian age occur locally throughout the area.Sedimentary rocks are exposed in the western quarter of the tunnel. These are the Entrada(?) Sandstone and Morrison Formation of Late Jurassic age, the Dakota Group of Early Cretaceous age, the Benton Shale of Early and Late Cretaceous age, and the Niobrara Formation and Pierre Shale of Late Cretaceous age. Underlying the sedimentary rocks exposed in the tunnel, and exposed to the west of the tunnel and intersected by drill holes along the tunnel line, are the Maroon Formation of Pennsylvanian and Permian age and the Lykins Formation of Permian and Triassic(?) age. These sedimentary rocks dip eastward toward the axis of the Front Range.Early during the Laramide orogeny the Williams Range thrust fault developed, and Precambrian rocks were superimposed on the Pierre Shale along the fault. After the period of thrusting the Montezuma Quartz Monzonite stock was emplaced. The Williams Range thrust fault, as a result, was folded upward, and the tunnel intersects the fault zone at two places. Between the eastern exposure of the thrust and the Montezuma stock is a sequence of shale and siltstone that becomes more metamorphosed as the stock is approached. This sequence of shale and siltstone is believed to be equivalent, for the most part, to part of the Pierre Shale to the west of the Williams Range thrust.Before and after the intrusion of the Montezuma stock, a series of dikes intruded the Precambrian units around the stock. The oldest dikes are augite and hornblende diorite. Other dikes contemporaneous in age and younger than the stock are latite porph...

show abstract

“…The Snake River arm is underlain by faulted Cretaceous shale, the Dakota quartzite, and the Morrison and Maroon formations (Lovering & Goddard 1950). Schist and gneiss of the Precambrian Idaho Springs formation and Swandyke gneiss ('A' and 'B' series rocks of Wahlstrom & Kim 1959) underlie much of the Snake River drainage basin, except where they are intruded by Tertiary igneous rocks. The eastern side of the basin lies largely within the Oligocene Montezuma quartz monzonite stock, and mineralization in the basin occurs primarily in Precambrian rocks to the east, south and south-west of the stock.…”

Section: Introductionmentioning

confidence: 99%

Mineralogical and geochemical investigation of sediment in the Snake River arm of the Dillon Reservoir, Summit County, Colorado, USA

et al. 2005

View full text Add to dashboard Cite

Mineralogical and chemical analyses of sediment in the Snake River arm of the Dillon Reservoir provided insight into the transport and fate of trace metals in this system, which provides potable water to the city of Denver in Colorado. The sediments contain metal hydroxide precipitates and sorbed trace metals that formed upstream in the Snake River and in Deer Creek, Peru Creek and other tributaries. Iron and trace metal concentrations in the sediments reach a maximum about halfway down the 3.3 km arm, with their distribution probably controlled by physical processes acting on the settling of precipitates entering the arm from the mouth of the Snake River. The concentration of molybdenum is at background concentration near the mouth of the Snake River, increasing towards the centre of the reservoir, where values are 10 times greater, owing to contamination from the Ten Mile Creek and Blue River arms of the reservoir. The results of a sediment-leaching experiment demonstrated that the relative ease of extraction with a decreasing pH value in the sediments is zinc > cobalt > copper > nickel > lead. Although most of the trace metals are low in concentration, or are strongly sorbed in the sediments, the relatively high concentration of zinc and its relatively high mobility make it a metal of potential concern in the reservoir.

show abstract

Precambrian Rocks of the Hall Valley Area, Front Range, Colorado

Cited by 10 publications

References 0 publications

Rock units of the Precambrian basement in Colorado

Rock units of the Precambrian basement in Colorado

General geology of the Harold D. Roberts Tunnel, Colorado

Mineralogical and geochemical investigation of sediment in the Snake River arm of the Dillon Reservoir, Summit County, Colorado, USA

Contact Info

Product

Resources

About