40Ar/39Ar ages from the rhyolite of Alder Creek, California: Age of the Cobb Mountain Normal-Polarity Subchron revisited

Turrin, B. D.; Donnelly‐Nolan, Julie M.; Hearn, B.C.

doi:10.1130/0091-7613(1994)022<0251:aaaftr>2.3.co;2

Cited by 94 publications

(34 citation statements)

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“…Full details of sample preparation and analysis are provided in the online supplementary material (Section S2). Samples were irradiated with splits of Alder Creek Sanidine neutron fluence monitor (1.186±0.006 Ma; Turrin et al 1994;Nomade et al 2005) at the Oregon State University TRIGA reactor, for between 0.55 and 13 h, using the CLICIT (cadmium lined in core irradiation tube) facility to minimise interaction with thermal neutrons that cause the 40 K(n, p) 40 Ar reaction and production of 36 Cl. Ar/Ar analysis was carried out using the MS1 Noble Gas Mass Spectrometer in the Isotope Geochemistry Laboratories at the University of Manchester.…”

Section: Samples and Petrographymentioning

confidence: 99%

Rhyolites at Kerlingarfjöll, Iceland: the evolution and lifespan of silicic central volcanoes

et al. 2010

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Kerlingarfjöll central volcano is Iceland's second largest outcrop of Quaternary rhyolite and is part of the Icelandic Western Rift Zone. Geochemical and Ar/Ar age data show that at least 21 different rhyolite eruptions have taken place at Kerlingarfjöll over the last 350 ka. Ar/Ar dating was carried out on samples of obsidian which showed variable reproducibility, illustrating the difficulty in dating young Icelandic volcanics. Nevertheless, reasonable estimates of eruption age have been derived for a number of eruptive units that are consistent with observed stratigraphy, enabling an understanding of the temporal evolution of Kerlingarfjöll. Two rhyolite magma types are present. The first is an older, low-Nb rhyolite that was erupted episodically along a cryptic curved fracture system, to form a discontinuous ring of rhyolite mountains, between 350 and 250 ka. This discontinuous ring is similar to structures observed at other volcanoes in Iceland, suggesting that the development of a curved fracture that acts as a pathway for episodic silicic eruptions is a feature of central volcano development. The second magma is a younger, high-Nb rhyolite that was erupted episodically between 250 and 68 ka in the northern part of Kerlingarfjöll, forming two clusters, both of which have areas of intense hydrothermal activity. Repose periods for rhyolite volcanism are thought to be on the order of tens of thousands of years, and it is possible that Kerlingarfjöll will erupt rhyolite again in the future.

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Section: Samples and Petrographymentioning

confidence: 99%

Rhyolites at Kerlingarfjöll, Iceland: the evolution and lifespan of silicic central volcanoes

et al. 2010

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“…Moreover, the literature is replete with examples to the contrary (e.g. Spell and McDougall, 1992;Turrin et al, 1994;Izett and Obradovich, 1994;Smith et al, 1996;Hilgen et al, 1997).…”

Section: Comparison Of Ar=ar and Astronomical Agesmentioning

confidence: 99%

Sedimentary cycles and volcanic ash beds in the Lower Pliocene lacustrine succession of Ptolemais (NW Greece): discrepancy between 40Ar/39Ar and astronomical ages

Steenbrink

Vugt

Hilgen

et al. 1999

Palaeogeography, Palaeoclimatology, Palaeoecology

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A high-resolution cyclostratigraphy for the rhythmically bedded lignite-marl sequences of the Lower Pliocene Ptolemais Formation is combined with 40 Ar= 39 Ar dating results of intercalated volcanic ash beds. Detailed field reconnaissance in three open-pit lignite mines reveals three end-member sediment types: lignites, composed primarily of organic material; grey marls, a mixture of carbonate and organic material; and beige marls, almost exclusively composed of carbonate. These lithologies are arranged in two basic types of sedimentary cycles: lignite-grey marl and lignite-beige marl cycles. A cyclostratigraphic composite section comprising 56 lignite-marl cycles is constructed which combines the consistent cycle patterns from three parallel sections. The concordant positions of 20 volcanic ash beds in these sections confirm the cyclostratigraphic correlations and indicate that the lignite-marl cycles result from regional, basin-wide forcing rather than lateral facies migrations. 40 Ar= 39 Ar ages on sanidine and biotite separates from nine volcanic ash beds were obtained by multiple total fusion and incremental-heating experiments. The 40 Ar= 39 Ar ages range between 5:00 š 0:05 and 4:04 š 0:04 Ma and are, in general, consistent with the stratigraphic order. A least-square linear regression using the measured 40 Ar= 39 Ar ages gives an average duration of 21:8 š 0:8 kyr per lignite-marl cycle. Evidently, the lignite-marl cycles in the Ptolemais Formation are linked to the precessional variation in the Earth's orbit through its influence on Mediterranean climate. For the first time, 40 Ar= 39 Ar dating results, totally independent from any other dating and or tuning technique, confirm the astronomical theory of climate change. The 40 Ar= 39 Ar ages of the volcanic ash beds show a constant ¾200 kyr (¾4.5%) age discrepancy with the astronomical ages of the same ash beds. This inconsistency remains difficult to explain. The discrepancy is unlikely to have resulted from erroneous astronomical ages, through incorrectness in the astronomical tuning, inaccuracies of the magnetostratigraphic data or the orbital time-series used, and=or errors in the APTS. The 40 Ar= 39 Ar dating results neither give clear indications for a possible source of error. From the excellent data set it is evident that neither loss of radiogenic 40 Ar, nor an underestimation of the contribution of Ca-and K-derived Ar isotopes could have caused the discrepancy. Moreover, the discrepancy is also beyond the errors in the systematic variables, like the decay constants of 40 K or the ages for the neutron-fluence monitors. © 1999 Elsevier Science B.V. All rights reserved. J. Steenbrink et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 152 (1999) 283-303

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“…It is unclear at this stage whether these outliers indicate heterogeneity in the sample population. The diagrams and the tabulated results show that the measured age for this standard (1.189 ± 0.005 Ma) is indistinguishable, at the 2σ confidence level, from the proposed values for this standard (1.186 ± 0.006, Turrin et al 1994;1.194 ± 0.007 Ma, Renne et al 1998).…”

Section: Alder Creek Sanidinementioning

confidence: 61%

“…Several standards are suitable as flux monitor and the choice of standard depends on the expected age for the sample to be analyzed. For young samples (< 4 Ma) we use the Alder Creek sanidine standard (1.186 ± 0.013 Ma) (Turrin et al 1994). For samples in the 2-100 Ma age range, we use Fish Canyon sanidine, which has an age of 28.02 ± 0.09 Ma (Renne et al 1998).…”

Section: Irradiation Proceduresmentioning

confidence: 99%

40Ar/39Ar geochronology at the Instituto de Geociências, USP: instrumentation, analytical procedures, and calibration

Vasconcelos

Onoe

Kawashita

et al. 2002

An. Acad. Bras. Ciênc.

102

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Laser heating 40 Ar/ 39 Ar geochronology provides high analytical precision and accuracy, µm-scale spatial resolution, and statistically significant data sets for the study of geological and planetary processes. A newly commissioned 40 Ar/ 39 Ar laboratory at CPGeo/USP, São Paulo, Brazil, equips the Brazilian scientific community with a new powerful tool applicable to the study of geological and cosmochemical processes.Detailed information about laboratory layout, environmental conditions, and instrumentation provides the necessary parameters for the evaluation of the CPGeo/USP 40 Ar/ 39 Ar suitability to a diverse range of applications. Details about analytical procedures, including mineral separation, irradiation at the IPEN/CNEN reactor at USP, and mass spectrometric analysis enable potential researchers to design the necessary sampling and sample preparation program suitable to the objectives of their study.Finally, the results of calibration tests using Ca and K salts and glasses, international mineral standards, and in-house mineral standards show that the accuracy and precision obtained at the 40 Ar/ 39 Ar laboratory at CPGeo/USP are comparable to results obtained in the most respected laboratories internationally. The extensive calibration and standardization procedures undertaken ensure that the results of analytical studies carried out in our laboratories will gain immediate international credibility, enabling Brazilian students and scientists to conduct forefront research in earth and planetary sciences.

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40Ar/39Ar ages from the rhyolite of Alder Creek, California: Age of the Cobb Mountain Normal-Polarity Subchron revisited

Cited by 94 publications

References 0 publications

Rhyolites at Kerlingarfjöll, Iceland: the evolution and lifespan of silicic central volcanoes

Rhyolites at Kerlingarfjöll, Iceland: the evolution and lifespan of silicic central volcanoes

Sedimentary cycles and volcanic ash beds in the Lower Pliocene lacustrine succession of Ptolemais (NW Greece): discrepancy between 40Ar/39Ar and astronomical ages

40Ar/39Ar geochronology at the Instituto de Geociências, USP: instrumentation, analytical procedures, and calibration

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