K-Ar and fission-track zircon ages of Cerro Toledo rhyolite tephra units in the Jemez Mountains, north-central New Mexico
No abstract available.
New Mexico↗
Geology topics
C. W. Naeser
Publications and source records attributed to C. W. Naeser.
Pleistocene rhyolite of the Mineral Mountains, Utah: Geothermal and archeological significance
Little-eroded rhyolitic tuffs, flows, and domes extend over about 25 km 2 along the western side of the Mineral Mountains, southwestern Utah, which is along the eastern edge of the Roosevelt KGBA (Known Geothermal Resource Area). Initial eruptions resulted in two low-viscosity lava flows of nonporphyritic rhyolite. These were followed by bedded pumice falls and nonwelded ash flows. The youngest activity produced at least nine viscous domes and small lava flows of rhyolite that contain 1-5 percent phenocrysts of quartz, plagioclase, sodic sanidine, and biotite; distinction between domes and eroded flow segments locally is difficult. Potassium-argon ages indicate that all the rhyolite of the Mineral Mountains was erupted between 0.8 and 0.5 m.y. ago. The rhyolite rests on dissected granite of the Mineral Mountains pluton, the largest intrusion in Utah, which has yielded published K-Ar ages of 9 and 15 m.y. A small older dissected rhyolite dome, about 8 m.y. old, occurs just west of the range front. Whether the young ages of the pluton represent time of intrusion or of later reheating, they, in conjunction with the Pleistocene rhyolite in the Mineral Mountains, do indicate a major late Cenozoic thermal anomaly, the size and age of which is significant to evaluation of the Roosevelt KGRA. The rhyolite is also the only known source of implement-grade obsidian in the southwest between eastern California and northern New Mexico.
Utah↗
New geochronologic and palaeomagnetic data for the hominid-bearing Hadar Formation of Ethiopia
A 2.6 Myr K/Ar age has been derived for a primary unreworked tuff high in the hominid-bearing Hadar Formation (Kada Hadar Member), stratigraphically above all the important fossil finds. A 2.6 Myr fission track age has been derived on zircons from this tuff. New K/Ar results on the Kadada Moumou basalt (Sidi Hakoma Member) suggest a 3.0 Myr age. Preliminary interpretation of a detailed continuous palaeomagnetic section through the formation indicates the existence of persistent normal and reversed sequences. With the radiometric age control this magnetic sequence appears to correlate with the Gauss Epoch. These initial results imply the fossil-rich Hadar Formation spans from somewhat older than 3.1 Myr to somewhat younger than 2.6 Myr. ?? 1977 Nature Publishing Group.
Nature↗
Fission-track dating of pumice from the KBS Tuff, East Rudolf, Kenya
Fission-track dating of zircon separated from two pumice samples from the KBS Tuff in the Koobi Fora Formation, in Area 131, East Rudolf, Kenya, gives an age of 2.44±0.08 Myr for the eruption of the pumice. This result is compatible with the previously published K–Ar and 40 Ar/ 39 Ar age spectrum estimate of 2.61±0.26 Myr for the KBS Tuff in Area 105, but differs from the more recently published K–Ar date of 1.82±0.04 Myr for the KBS Tuff in Area 131. This study does not support the suggestion that pumice cobbles of different ages occur in the KBS Tuff
Nature↗
Pre-Eocene rocks of Java, Indonesia
The exposed pre-Eocene rocks of Java can be divided into two compound units for purposes of reconnaissance mapping and structural interpretation: a sedimentary sequence and melange. The sedimentary sequence consists of moderately deformed and little-metamorphosed conglomerate, sandstone, mudstone, claystone, chert, and limestone. The melange consists of a chaotic mechanical mixture of rocks identical to those of the sedimentary sequence and their metamorphic equivalents, such as schist, phyllite, quartzite, and marble. In addition, it contains a large proportion of quartz porphyry and smaller amounts of granite, basalt, gabbro, peridotite, pyroxenite, and serpentinite. The sedimentary sequence is at least partly of Early Cretaceous age and the melange is of Early Cretaceous to very early Paleocene age. They are overlain unconformably by Eocene rocks. The presence in the melange of blocks of quartz porphyry and granite is not easily reconcilable with current plate tectonic concepts in which the sites of formation of melange and plutonic rocks should be hundreds of kilometres apart.
Java↗
Fission-track ages of sphene and apatite of granitic rocks of the Salinian block, Coast Ranges, California
Fission-track ages have been determined on apatite and sphene from granitic rocks of the Salinian block, California Coast Ranges. The 26 age determinations on sphene range between 68 and 93 m.y. The 24 age determinations on apatite have a greater variation, ranging from 3 to 74 m.y. None of the fission-track ages appear to reflect times of intrusion. The Pinnacles volcanic field of Miocene age apparently has thermally affected apatite ages in the central Gabilan and eastern Santa Lucia Ranges. Reduced apatite ages in the area between the Farallon Islands and the Monterey Peninsula may also be the result of Miocene volcanic activity, but the evidence is less conclusive. Fission-track ages on sphene correlate closely with previously determined potassium-argon ages on hornblende and biotite but show an unexplained "bimodal" age distribution, the ages in the Gabilan and Santa Lucia Ranges being slightly, but consistently, lower (avg 75 m.y.) than the ages for terrane to the north and south (avg 85 m.y.) The overall pattern of the sphene and apatite fission-track ages, distinctly different from that of the central Sierra Nevada, may be a "fingerprint" of correlative value in locating the parent terrane of the "ripped-off" Salinian block.
California↗
Comparison of fission-track, K-Ar, and Rb-Sr radiometric age determinations from some granite plutons in Maine
Fission-track ages have been determined on eight apatite and four sphene concentrates separated from plutonic rocks in Maine. K-Ar and Rb-Sr ages for some of these rocks were previously published. In northeastern Maine the whole-rock Rb-Sr, biotite K-Ar, and apatite fission-track ages are concordant at 400-420 million years, whereas in south-central Maine the apatite fission-track age is 150 m.y. and the biotite K-Ar age is about 250 m.y. At intermediate positions along the traverse the whole-rock Rb-Sr, biotite K-Ar, and sphene fission-track ages agree fairly well in the range 390-325 m.y., but the apatite fission-track ages are all about 100 m.y. younger. This pattern is consistent with the hypothesis of burial metamorphism and uplift as proposed in 1970 by Zartman, Hurley, Krueger, and Giletti to explain the abundance of Permian K-Ar ages in central New England.
Maine↗
Zircon fission-track ages of Pearlette family ash beds in Meade County, Kansas
Pearlette family volcanic ash beds at two faunally important late Cenozoic localities near Meade, Meade County, Kansas, are very similar in chemical and mineralogic composition, yet their zircon microphenocrysts have markedly different fission-track ages. Zircon microphenocrysts from type B Pearlette volcanic ash underlying sediments that contain the Borchers local fauna of Hibbard are various shades of pink and have a fission-track age of 1.9 ± 0.1 m.y. In contrast, zircon microphenocrysts from type O Pearlette volcanic ash overlying sediments that contain the Cudahy local fauna of Hibbard are colorless and have a fission-track age of 0.6 ± 0.1 m.y. These fission-track ages are in good agreement with K-Ar ages on the probable source material in Yellowstone National Park.
Kansas↗
Zircon fission-track ages of Pearlette family ash beds in Meade County, Kansas
Pearlette family volcanic ash beds at two faunally important late Cenozoic localities near Meade, Meade County, Kansas, are very similar in chemical and mineralogic composition, yet their zircon microphenocrysts have markedly different fission-track ages. Zircon microphenocrysts from type B Pearlette volcanic ash underlying sediments that contain the Borchers local fauna of Hibbard are various shades of pink and have a fission-track age of 1.9 ± 0.1 m.y. In contrast, zircon microphenocrysts from type O Pearlette volcanic ash overlying sediments that contain the Cudahy local fauna of Hibbard are colorless and have a fission-track age of 0.6 ± 0.1 m.y. These fission-track ages are in good agreement with K-Ar ages on the probable source material in Yellowstone National Park.
Kansas↗
Search for plutonium-244 tracks in mountain pass bastnaesite
WE have found that bastnaesite, a rare earth fluorocarbonate, from the Precambrian Mountain Pass deposit has an apparent Cretaceous fission track age, and hence does not reveal any anomalous fission tracks due to 244 Pu.
Nature↗
A Cuban tektite
A large tektite from Cuba is classified with other North American tektites on the basis of its age. The major-element chemistry, oxygen isotopic composition, refractive index and density of the Cuban tektite are within the ranges exhibited by bediasites.
Geochimica et Cosmochimica Acta↗
Fission-track and K-Ar ages of Tertiary ash-flow tuffs, north-central Nevada
Ages obtained from three Tertiary ash-flow tuffs in central Nevada by fission-track and K-Ar dating are concordant. Samples dated by these methods from the same localities give the same age within the limits of analytical uncertainty. Samples of three units from widely separated localities were dated further to confirm the concordance of the dating methods and to establish that ages can be used, in conjunction with normal geologic techniques, as a criteria for correlation. The minerals dated by K-Ar were biotite and sanidine; and sphene zircon and apatite were used to determine the fission track ages. The Bates Mountain Tuff was dated at 24.0 m.y. (F.T.) and 24.0 m.y. (K-Ar). The Fish Creek Mountains Tuff has a fission-track age of 24.4 m.y., and a K-Ar age of 23.9 m.y. The average fission-track age for the Caetano Tuff is 34.9 m.y., and it has an average K-Ar age of 32.3 m.y. The amount of analytical uncertainty is slightly greater in the fission track method. Sampling, preparation, and determination of the age by the fission-track method is competitive with the K-Ar method.
Nevada↗
Etching fission tracks in zircons
A new technique has been developed whereby fission tracks can be etched in zircon with a solution of sodiuim hydroxide at 220°C. Etching time varied between 15 minutes and 5 houtrs. Colored zircon required less etching time than the colorless varieties.
Science↗
Fission-track ages of accessory minerals from granitic rocks of the central Sierra Nevada batholith, California
Ages of apatite, sphene, allanite, epidote, and garnet from plutonic rocks of the central Sierra Nevada and Inyo Mountains have been determined by the fission-track method. Ages of 44 specimens of apatite range from 54 to 128 m.y. Oldest apatites generally occur in rocks from the western portion of the batholith; youngest are from granitic rocks along the eastern slope of the Sierra Nevada. Thirty-four specimens of sphene have been dated and range in age from 71 to 118 m.y. Within experimental error, all sphenes are as old as, or older than, coexisting apatites. The oldest sphene is from granitic rock of the Inyo Mountains; however, sampled rocks from the western Sierra Nevada do not contain sphene. The youngest sphenes are generally from rocks slightly west of the Sierran crest.
California↗