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R. F. Marvin

Publications and source records attributed to R. F. Marvin.

At least 19 recordsLinked to original sources
USGS1989

Significance of new potassium-argon ages from the Goldens Ranch and Moroni Formations, Sanpete-Sevier Valley area, central Utah

Exposures of volcanic-sedimentary strata are widely distributed within central Utah. We believe that these volcanic and stratified sedimentary rocks, known by different formational names in different parts of this region, are, in fact, segments of one and the same suite of rocks that formed during the early and middle Tertiary. The volcanic-sedimentary complex is exposed on both sides of a north-trending lowland formed by the collinear Juab and Sevier Valleys. West of the lowland, the complex has been named the "Goldens Ranch Formation" east of the lowland, it has been called the "Moroni Formation."; Both formations are stratigraphically alike in that each consists of a lower unit composed predominantly of water-laid, variably cemented sediments and sedimentary rocks with some tuff beds near the base, and an upper unit of intermediate-composition volcanic rocks, chiefly ash-flow tuffs, and volcanic breccias. Both formations contain abundant exotic clasts of andesite, tan and purple quartzite, and dark blue limestone and dolomite. Both formations are folded and faulted along with the underlying sedimentary units. Potassium-argon ages indicate that both the Goldens Ranch and Moroni Formations formed during the late Eocene to middle Oligocene. The geochronology and stratigraphic relations are strong evidence that the Goldens Ranch and Moroni Formations are correlative, and that they are one and the same depositional unit. During the latest Oligocene-earliest Miocene, minor monzonitic bodies intruded sedimentary units in the area. The new K-Ar data bear on the matter of the origin of the complex structural deformation in central Utah. Different workers have attributed the singular deformation either to recurrent episodes of compression stemming from the Sevier orogeny, or to repeated episodes of salt diapirism. We recognize two sequences of repeated deformation: one that occurred prior to deposition and consolidation of the Goldens Ranch and Moroni Formations, and a second that occurred after these formations were emplaced, in essence, after early Oligocene time. The Sevier orogeny ended in Paleocene time; thus, the compression and thrusting stemming from the Sevier orogeny could be responsible for the structural complexity that marks pre-Paleocene units. These same orogenic forces do not seem to be viable explanations for the broad flexures and monoclinal downwarps that mark the Goldens Ranch, Moroni, and younger formations. In our view, multiple episodes of salt diapirism more reasonably explain the structural complexity in central Utah.

Utah↗
USGS1986

Ages of igneous and hydrothermal events in the Round Mountain and Manhattan gold districts, Nye County, Nevada

About 60 new isotopic age determinations help clarify the geologic history of the Round Mountain and Manhattan gold districts, Nevada. Cretaceous granite of Shoshone Mountain, southeast of Round Mountain, was emplaced about 95 m.y. ago and was domed, metamorphosed, and mineralized with tungsten-bearing quartz veins 80 m.y. ago. The granite of Pipe Spring, south of Manhattan, was emplaced probably at about 80 m.y. ago. Mineralization associated with the Pipe Spring body occurred about 75 m.y. ago. A granodiorite stock and associated rhyolite and andesitc dikes intruded the granite southeast of Round Mountain 36 m.y. ago; apparently base and precious metals mineralization accompanied their intrusion, but mineralization has not been dated isotopically. Ash-flow tuff at Round Mountain was emplaced about 26 m.y. ago, the Manhattan caldera formed about 25 m.y. ago, and gold mineralization at Round Mountain occurred at about 25 m.y. ago. Gold mineralization at Manhattan took place 16 m.y. ago.The isotopic data allow interpretation of the cooling histories of some of the igneous rocks and suggest possible thermal events that reset mineral ages.

Economic Geology↗
USGS1986

Late Cretaceous stratigraphy, deformation and intrusion in the Madison Range of southwestern Montana ( USA).

Dating of orogenic rock units in the central part of the Madison Range shows that Laramide deformation was virtually completed by the end of the Cretaceous. Early Campanian K-Ar dates of about 79 m.y. were obtained from welded tuffs in the basal part of the Livingston Formation, a volcanic and volcaniclastic assemblage that is conformable with underlying Cretaceous clastic rocks and with the overlying Sphinx Conglomerate. The Sphinx and the Livingston were deformed by the Hilgard fault system which extends along the western side of the southern two-thirds of the range. This north-trending fault system represents the culmination of Laramide shortening within the range. Dating of hornblende indicates an approximate date of 68-69 m.y. B.P. for emplacement of the igneous suite. The dacite postdates movement along faults of the Hilgard fault system, and postdates the synorogenic Sphinx Conglomerate. -from Authors

Geological Society of America Bulletin↗
USGS1984

Geochronometric and lead isotope data on samples from the Wallace 1 degree by 2 degrees Quadrangle, Montana and Idaho

Most of the bedrock in the Wallace quadrangle belongs to the Belt Supergroup, a thick (about 18,000 m) sequence of generally fine-grained clastic and carbonate rocks of Middle Proterozoic age. Regional metamorphism prior to Cambrian time prograded the Belt rocks to greenschist facies, and some metal-bearing veins were emplaced in fractures. The Belt rocks were intruded in Late Proterozoic time by basic dikes and sills.

Idaho, Montana↗
USGS1980

Pliocene intrusive rocks and mineralization near Rico, Colorado

Fission-track and potassium-argon studies of intrusive rocks in the vicinity of Rico, Colorado, have shown that there are at least two periods of igneous activity and that significant ore mineralization is associated with alaskites and latites that are 3 to 5 m.y. old. Discordant fission track ages of apatite and zircon in the older rocks reveal a major heat source that cooled in late Miocene or early Pliocene and is centered under the mineralized rocks near the townsite of Rico. This heating may indicate the presence of a buried stock that is related to the mineralization.

Colorado↗
USGS1980

Geochemistry, strontium isotope data, and potassium-argon ages of the andesite-rhyolite association in the Padang area, West Sumatra

Quaternary volcanoes in the Padang area on the west coast of Sumatra have produced two-pyroxene, calc-alkaline andesite and volumetrically subordinate rhyolitic and andesitic ash-flow tuffs. A sequence of andesite (pre-caldera), rhyolitic tuff and andesitic tuff, in decreasing order of age, is related to Maninjau caldera. Andesite compositions range from 55.0 to 61.2% SiO2 and from 1.13 to 2.05% K2O. Six K-Ar whole-rock age determinations on andesites show a range of 0.27 ?? 0.12 to 0.83 ?? 0.42 m.y.; a single determination on the rhyolitic ashflow tuff gave 0.28 ?? 0.12 m.y. Eight 57Sr/26Sr ratios on andesites and rhyolite tuff west of the Semangko fault zone are in the range 0.7056 - 0.7066. These ratios are higher than those elsewhere in the Sunda arc but are comparable to the Taupo volcanic zone of New Zealand and calc-alkaline volcanics of continental margins. An 87Sr/86Sr ratio of 0.7048 on G. Sirabungan east of the Semangko fault is similar to an earlier determination on nearby G. Marapi (0.7047), and agrees with 87Sr/86Sr ratios in the rest of the Sunda arc. The reason for this distribution of 87Sr/86Sr ratios is unknown. The high 87Sr/86Sr ratios are tentatively regarded to reflect a crustal source for the andesites, while moderately fractionated REE patterns with pronounced negative Eu anomalies suggest a residue enriched in plagioclase with hornblende and/or pyroxenes. Generation of associated andesite and rhyolite could have been caused by hydrous fractional melting of andesite or volcanogenic sediments under adiabatic decompression. ?? 1980.

Journal of Volcanology and Geothermal Research↗
USGS1979

Pliocene intrusive rocks and mineralization near Rico, Colorado

Fission-track and potassium-argon studies of intrusive rocks in the vicinity of Rico, Colorado, have shown that at least two periods of igneous activity occurred and that significant ore mineralization is associated with alaskites and latites that are 3 to 5 million years old. Discordant fission-track ages of apatite and zircon in the older rocks reveal a major heat source, centered under the mineralized rocks near the townsite of Rico, that cooled in late Miocene or early Pliocene time. This heat source may indicate the presence of a buried stock that is related to the mineralization.

Colorado↗