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Richard F. Marvin

Publications and source records attributed to Richard F. Marvin.

17 recordsLinked to original sources
USGS1977

Age and tectonic setting of lower Paleozoic alkalic and mafic rocks, carbonatites, and thorium veins in South-central Colorado

Alkalic igneous rocks were emplaced into heterogeneous terrane of Precambrian X and Precambrian Y rocks about 570 m.y. ago (Cambrian or upper Precambrian) in the Powderhorn area in Gunnison County and about 520 m.y. ago (Cambrian) in the McClure Mountain, Gem Park, and Democrat Creek areas in the northern Wet Mountains, Fremont and Custer Counties. The radiometric ages are based upon studies by K-Ar, Rb-Sr, and fission-track methods. Associated with these alkalic rock complexes are numerous thorium-bearing veins and red syenite dikes; some, if not all, in the northern Wet Mountains were formed about 495 m.y. ago. Diabase, gabbro, and other mafic dikes appear to be slightly younger than the thorium veins in the Powderhorn area and both older and younger in the Wet Mountains region. In the Powderhorn district, an older group of syenites also intruded Precambrian rocks as plugs or small stocks about 1350-1400 m.y. ago. The various dike rocks and the thorium veins were formed in extensive, deep fractures, indicating a condition of tension or shear in this part of the crust during Cambrian or very late Precambrian to Ordovician time. The localized alkalic magmatisin may reflect melting spots in the mantle. In the two principal areas, 135 km apart, the episodes of alkalic magmatism differ in age by about 50 m.y., the younger toward the east. The age relations might be explained by migration of the sites of localized melting or volatile enrichment in the mantle or westward movement of the continent above a single site.

Colorado↗
USGS1977

Potassium-argon geochronology of some metamorphic, igneous, and hydrothermal events in Puerto Rico and the Virgin Islands

Potassium-argon ages of hornblende, biotite, and whole rocks in Puerto Rico include the following: 126 m.y. for amphibolites in the southwest part of the island; 109 m.y. for the oldest known quartz diorite plutons; 88 to 65 m.y. for emplacement of various quartz diorite and granodiorite batholiths and stocks; 38 to 46 m.y. for intrusions of quartz diorite porphyry stocks and their hydrothermal alteration and mineralization. These intrusions are the youngest known igneous rocks in Puerto Rico. In addition, a 35-m.y. age was determined for hornblende and biotite from the Virgin Gorda batholith. Although widespread hydrothermal alteration as old as 75 m.y. is known in Puerto Rico, all important copper deposits are related to the 38- to 46-m.y. old intrusions.

Puerto Rico↗
USGS1975

The Oligocene volcanic center at Eureka, Nevada

A volcanic center covering an area of about 80 km 2 near Eureka, Nev., and active in the early Oligocene, is characterized by rhyolitic, rhyodacitic. and andesitic pyroclastic rocks, lava flows, and shallow intrusive bodies. These rocks were emplaced as intertonguing and interpenetrative units during a 5-m.y. interval; most of the volcanism was in the last 3 million years of this period (36 to 33 m.y. ago).

Nevada↗
USGS1975

Age provinces in the basement rocks of Liberia

Fourteen new Rb-Sr ages and 17 new K-Ar ages, when combined with published ages, confirm the previous subdivision of the basement rocks of Liberia into 3 age provinces. The Liberian age province was metamorphosed and intruded 2,700 m.y. ago, but the data suggest that many of the rocks of this province are probably considerably older. The Eburnean age province was metamorphosed approximately 2,150 m.y. ago. Rocks of the Pan-African age province were originally part of the Liberian province, but underwent a relatively intense metamorphism 500 m.y. ago. The K-Ar age patterns suggest that the Pan-African province was uplifted relative to the Liberian province sometime after 500 m.y. ago, but fission-track ages of apatites indicate that any such relative vertical displacements must have occurred prior to 120 m.y. ago.

Journal of Research of the U.S. Geological Survey↗
USGS1974

Geologic framework of the Kuluncak-Sofular Area, East-Central Turkey, and K-Ar ages of igneous rocks

The Kuluncak-Sofular area, located about midway between Sivas and Malatya in east-central Turkey is underlain by a variety of sedimentary, volcanic, and intrusive rocks. The sedimentary rocks have been deposited on a pre-Campanian serpentinite basement and include Cretaceous conglomerate, graywacke, tuff, and limestone; Eocene arkosic sandstone, conglomerate, and limestone; and Miocene limestone and dolomite. K-Ar ages determined for volcanic and intrusive rocks from the same area are 75.5 m.y. for alkalic diabase that intrudes the Upper Cretaceous sedimentary rocks; 74.3 and 71.1 m.y. for trachyte that partly overlies and partly intrudes the same Upper Cretaceous sequence; 65.2 m.y. for alkalic syenite that intrudes Upper Cretaceous limestone; 18.7 to 16.8 m.y. for andesite and basalt that overlie middle to late Eocene sedimentary rocks; and 14.1 m.y. for a dacite plug that cuts Miocene limestone. © 1974 Geological Society of America.

Geological Society of America Bulletin↗
USGS1974

A tabulation of K-Ar, Rb-Sr, and Pb-α ages obtained for materials within the United States (including Alaska and Hawaii) during the years 1965 through 1968

This tabulation of ages has been made as a convenience to anyone desiring a quick reference to ages published in the United States and Puerto Rico from 1965 through 1968. This tabulation does not include all published K-Ar, Rb-Sr, or Pb-α ages, but is probably 98 percent complete. Many of the radiometric ages published in abstracts, footnotes, personal communications, and even some articles are not included as sample localities are lacking or are not sufficiently detailed to be of value. Such ages are often published in a subsequent article with detailed sample locations and geologic interpretation. There may be some duplication of ages in this tabulation. The references listed are either the original source for an age or the best source in regard to sample location, decay constants, interpretation, etc. A minor number of unpublished radiometric ages from Ph.D. or M.S. theses are also listed in this tabulation. The tabulated ages are systematized according to year and state. All ages published during a specific year (i.e. 1965) are grouped together, with the ages listed under the name of the state in which the sample was collected. The states are alphabetized. The dated sample is described as to rock type, location, material analyzed, age(s) determined, radiometric method used, and published reference (by first author only). The complete reference is listed at the end of the tabulation for each specific year. To answer questions about geologic interpretation, decay constants, or location, one must review the source reference.

Open-File Report↗
USGS1974

A tabulation of K-Ar, Rb-Sr and Pb-alpha ages obtained for materials within the United States (including Alaska and Hawaii) during the years 1969 through 1971

This tabulation of ages has been made as a convenience to anyone desiring a quick reference to ages published in the United States from 1969 through 1971. This tabulation does not include all published K-Ar, Rb-Sr, or Pb- α ages but is probably 98% complete. Many of the radiometric ages published in abstracts, footnotes, or personal communications are not included as sample localities are lacking or are not sufficiently detailed to be of value. Such ages are often published in a subsequent article with detailed sample locations and geologic interpretation. There may be some duplication of ages in this tabulation. The references listed are either the original source for an age or the best source in regard to sample location, decay constants, interpretation, etc. A few fission-track ages also are listed.

Open-File Report↗
USGS1973

Radiometric ages of intrusive rocks in the Little Belt Mountains, Montana

Radiometric ages indicate that most, if not all, of the major intrusions in the Little Belt Mountains, central Montana, were emplaced during the Eocene epoch, between 48 and 54 m.y. ago. In the Hughesville area, igneous activity continued, or was episodic until 42 m.y. ago. As a result of the continued igneous activity, radiometric ages in the Hughesville area can be interpreted either as primary ages or as reset ages.

Montana↗
USGS1971

Mesozoic granitic rocks in northwestern Nevada: A link between the Sierra Nevada and Idaho batholiths

Extensive areas in northwestern Nevada are underlain by granodiorite and quartz monzonite plutons, as well as less common smaller bodies of quartz diorite. Twenty-six K/Ar age determinations on rocks from this suite range from about 175 to 85 m.y., but most of the plutons are between 105 and 85 m.y. old. This Late Cretaceous intrusive epoch extending from 105 to 85 m.y. ago is here named the Lovelock intrusive epoch. Twenty-three whole-rock chemical analyses show that the granitic rocks of northwestern Nevada form a homogeneous differentiation series with a narrow range in major element distribution. The granitic plutons of northwestern Nevada are chemically and petrographically indistinguishable from granitic intrusives of equivalent age in the Sierra Nevada and Idaho batholiths, and form a link between these two major batholiths.

California, Idaho, Nevada↗
USGS1971

Radiometric age (Late Ordovician) of the Quincy, Cape Ann, and Peabody Granites from eastern Massachusetts

A geochronologic study of several intrusive bodies of alkalic granite from eastern Massachusetts yields the following radiometric ages (in millions of years). Rock unit Amphibole K-Ar Whole-rock Rb-Sr isochron Pb 207 /Pb 206 zircon Quincy Granite 430-458 313 ± 22 437 ± 32 Cape Ann Granite 374-397 435 ± 6 452 ± 10 Peabody Granite 350-403 367 ± 24 435 + 12 445 ± 22 The zircon ages show only mild internal discordancies and most diffusion models used to discuss U-Th-Pb isotopic systematics would give a true age about equal to that of the Pb 207 /Pb 206 value. When plotted on a concordia diagram, the zircon data indicate a time of emplacement of 450 ± 25 m.y. for all three granite bodies. This Late Ordovician age for post-tectonic granites suggests that revisions in the commonly accepted geologic interpretation of eastern Massachusetts may be required. Previously, because of their massive, undeformed nature, the alkalic rocks were generally regarded as being Mississippian or Devonian in age and younger than the Early to Middle Devonian Acadian orogeny. The amphibole K-Ar and whole-rock Rb-Sr systems have responded in a complex way to postcrystallization disturbances. We interpret the pattern of ages for the Quincy Granite to reflect a late Paleozoic(?), low-temperature alteration that accompanied extensive faulting, and the patterns of ages for the Cape Ann and Peabody Granites to reflect a Devonian heating possibly related to contact metamorphism by a nearby mafic pluton.

Massachusetts↗
USGS1970

Radiometric ages and stratigraphic sequence of volcanic and plutonic rocks, southern Nye and western Lincoln Counties, Nevada

The geochronology of Tertiary igneous events at the Nevada Test Site and adjacent area is outlined by 36 recently determined K-Ar ages, together with other published K-Ar ages. The first evidence of Tertiary igneous activity is the ash-fall bedded tuffs in the Horse Spring Formation. One such tuff has been dated as 29 m.y. old (late Oligocene). Other ash-flow tuffs and lavas formed during the Miocene and Pliocene, according to radiometric age determinations. The youngest ash-flow tuff in this area is about 6 m.y. old. Great volumes of ash and lava were spewed forth 13 to 11 m.y. ago to form the Paintbrush and Timber Mountain Tuffs. Sixteen replicate age determinations on minerals from four densely welded ash-flow tuffs from these formations gave a pooled standard deviation of about ± 2 percent error, provided anomalous ages were rejected on the basis of rock alteration or analytical difficulties. In the Air Force Gunnery Range, just north of the test site, K-Ar ages suggest that the oldest ash flows, the Monotony Tuff, were emplaced 27.6 m.y. ago (late Oligocene) and were followed by outpourings of lava and ash throughout most of the Miocene. Youngest dated lava is about 13 m.y. old. In the southern Egan and northern Seaman Ranges of central Nevada, the Needles Range (?) Formation has an averaged K-Ar age of about 30 m.y., which compares closely with 29.2 m.y., the average of four earlier K-Ar ages determined by other investigators on known Needles Range Formation in eastern Nevada and western Utah. K-Ar ages given by micas from two exposed plutons in the Nevada Test Site suggest emplacement of these plutons at about 93 m.y. ago (early Late Cretaceous), although earlier emplacement in the Mesozoic would be more consistent with Pb-α ages

Nevada↗
USGS1970

Use of Ar36 to Evaluate the Incorporation of Air by Ash Flows

The Ar 36 content of densely welded glasses from ash-flow units provides a means by which the amount of air entrapped and subsequently resorbed by the glasses during compaction and welding may be calculated. The amount of air measured in glasses from nine upper Tertiary ash-flow sheets in the western United States ranges from 0.033 to 13 ppm; median is about 1 ppm. These values are very small compared with the total amounts of volatiles which probably were incorporated during welding. The data strongly suggest that large volumes of air are not incorporated by ash flows during their eruption and lateral movement.

California, Idaho, Nevada↗