Données sur Potassium et Argon (de 1976 à 1984) Dans quelques Echantillons Géochimiques de Reference

Zimmermann, J.-L.; Vernet, M.; Guyetand, G.; Dautel, D.

doi:10.1111/j.1751-908x.1985.tb00449.x

Cited by 18 publications

(12 citation statements)

References 8 publications

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“…The 40 Ar* contents range between 2.712 and 2.800 × 10 −10 mol/g, yielding a mean of (2.755 ± 0.042) × 10 −10 mol/g. This value is slightly lower than the ones determined by Flisch and Zimmermann et al Nevertheless, the weighted mean age obtained here, 18.2 ± 0.1 Ma (Figure A) for a K value of 8.68%, agrees with more recent measurements employing the 39 Ar/ 40 Ar step‐heating method on sub‐milligram samples for which age spectra suggest apparent ages of 17–18 Ma . These authors evidenced an inverse grain size – age relationship, with the Cl‐poor fine phengite being older than the Cl‐rich coarse muscovite.…”

Section: Dating Unknownssupporting

confidence: 87%

“…Flich compiled 24 results obtained from different laboratories, showing that the 40 Ar* contents range between 2.741 and 2.978 × 10 −10 mol/g with a mean of (2.812 ± 0.011) × 10 −10 mol/g. Zimmermann et al measured 40 Ar* contents of 2.790 and 2.795 10 −10 mol/g, which are consistent with the previous measurements.…”

Section: Dating Unknownssupporting

confidence: 84%

“…The 40 Ar* contents range between 2.712 and 2.800 × 10 −10 mol/g, yielding a mean of (2.755 ± 0.042) × 10 −10 mol/g. This value is slightly lower than the ones determined by Flisch 33 and Zimmermann et al 34 Nevertheless, the weighted mean age obtained here,…”

Section: Dating Unknownscontrasting

confidence: 75%

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A new unspiked K‐Ar dating approach using laser fusion on microsamples

Wang

Shi

Guillou

et al. 2019

Rapid Comm Mass Spectrometry

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Rationale Issues induced by neutron irradiation makes 40Ar/39Ar dating inapplicable in some cases. The first issue is 37Ar and 39Ar recoil effects during irradiation that affect fine‐grained minerals (<50 μm), such as lunar rocks, glassy groundmass, supergene minerals (e.g., illite, glauconite, Mg‐oxide, etc.). The second issue from neutron irradiation is the high radioactivity gain of iron‐rich samples such as pyrite, and the third is the production of interference nuclides during irradiation. The inherent drawbacks of conventional K‐Ar and current unspiked K‐Ar dating make it difficult to assess the reliability of age results. Methods A new approach is proposed using well‐calibrated 40Ar/39Ar standard minerals to directly quantify 40Ar, 38Ar and 36Ar. Fish Canyon sanidine (FCs), B4M muscovite and MMhb‐1 hornblende, the widely used international standard minerals, were analyzed as unknowns to test the approach. Argon isotope analyses were carried out on a noble‐gas mass spectrometer using laser fusion on microsamples (n × 0.01 to n × 0.2 mg). A new isochron – an “inverse isochron” for K‐Ar dating – was designed. Results FCs and B4M yielded apparent and inverse isochron ages of 28.1 ± 0.1 and 28.0 ± 0.3 Ma, 18.2 ± 0.1 and 18.2 ± 0.5 Ma, which are consistent with the recommended ages, while the MMhb‐1 presented lower apparent and inverse isochron ages (510.8 ± 4.8 and 512.3 ± 17.0 Ma) than the recommended ones. The initial argon compositions for the three standard minerals are 299.2 ± 205.3 (FCs), 294.0 ± 16.4 (B4M) and 290.9 ± 203.1 (MMhb‐1), agreeing with that of air. Conclusions The proposed approach potentially overcomes the issues of 40Ar/39Ar rising from irradiation and the drawbacks of K‐Ar. By using laser fusion on multiple microaliquots from a same sample, this approach can produce accurate and precise K‐Ar ages and give an inverse isochron. This new approach may provide an alternate dating method of geochronology based on argon isotopes.

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Section: Dating Unknownssupporting

confidence: 87%

Section: Dating Unknownssupporting

confidence: 84%

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A new unspiked K‐Ar dating approach using laser fusion on microsamples

Wang

Shi

Guillou

et al. 2019

Rapid Comm Mass Spectrometry

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“…The absence of 39Ar loss on chloritized biotites affected by 39Ar recoil was demonstrated by Ruffet et al (1991). To test a hypothetical 39Ar loss, a conventional K-Ar experiment was performed on sample G 65 at the CRPG-CNRS laboratory of Nancy, France (see Zimmermann et al, 1985, for the general procedure). An age of 32.8 k 3.9 Ma (40Ar = 6.55 X lov6 cc/g; atm = 91.3%) similar to the 40Ar/39Ar ages was obtained and thus precludes a high amount of 39Ar loss by recoil in that sample.…”

Section: Discussion Of 40ar/39ar Resultsmentioning

confidence: 99%

Time-pressure and temperature constraints on the formation of Colombian emeralds; an 40 Ar/ 39 Ar laser microprobe and fluid inclusion study

Cheilletz¹,

Féraud²,

Giuliani³

et al. 1994

Economic Geology

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Two Colombian deposits belonging to the western emerald belt of the Eastern Cordillera, namely Coscuez and Quipama-Muzo, hosted in Lower Cretaceous black shales, have been dated for the first time by 4oAr/39Ar induction and laser microprobe methods on contemporaneous greenish Cr-V-rich K mica aggregates consisting of muscovite as a dominant phase 5 kaolinite, 5 paragonite, quartz, ? albite, and ? chlorite, pyrite, and calcite. Contamination of the K mica aggregates by wall-rock impurities is eliminated by in situ 40Ar/39Ar laser spot analysis. Two distinct plateau and spot fusion ages of 35 to 38 Ma and 31.5 to 32.6 Ma were obtained for the Coscuez and Quipama samples, respectively, i.e., a late Eocene to early Oligocene age. Concordant conventional K-Ar ages show that in spite of the small size of these micas, they did not suffer significant 39Ar loss d u e to recoil during irradiation of the samples. Internal 39Ar recoil may explain the slight disturbances observed on the age spectra. Microthermometry, Raman spectroscopy, and SEM experiments performed on fluid inclusions trapped in emerald crystals from the Coscuez deposit show that the hydrothermal fluids are complex HzO-NaC1-CaClz-KCl-CO,-N, brines (38 wt % NaCl equiv). Constrained by the 40Ar/39Ar age determinations, the Eastern Cordillera subsiding model, and the assumption of lithostatic confining pressures, isochoric extrapolations lead to a pressure-temperature estimate of 1.06 to 1.12 kbars and 290" to 360°C for the emerald deposition. The P-T evaluation is in agreement with the paragenesis accompanying the emerald deposition. A moderate-temperature epigenetic hydrothermal-sedimentary model is proposed for Colombian emerald genesis. This model makes use of the following points: (1) the depth of hydrothermal circulation within the Lower Cretaceous series, (2) a basinal origin of mineralizing fluids as inferred from oxygen and carbon isotope data, (3) an evaporitic source for the NaCl sulfate-rich brines trapped within emerald crystals, as deduced from sulfur isotope data, (4) a likely source of the metallic components, and particularly Be, Cr, and V, being the black shale reservoir, and (5) the timing of hydrothermal circulation and emerald vein formation in relation to Eastern Cordillera tectonic evolution-in particular, the strong shortening episode beginning during the Eocene. F 364 CHEILLET2 ET AL.

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“…2). A more accurate measurement of argon is undertaken in potassic materials (Zimmermann et al, 1985) using another mass spectrometer, with 38Ar as a spike.…”

Section: Separation Of Gasesmentioning

confidence: 99%

Manometric and mass spectrometric analysis of fluids in geological meterials.

Zimmermann

Jambon²,

Guyetand

1988

Geochem. J.

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A procedure of volatile analysis in rocks which permits quantitative estimation of all the volatile species of any geological interest is presented and illustrated by several examples. Gas extraction is per formed either by vacuum crushing or heating. A separation line using cold traps, oxidation (CO to CO2) and reduction (H20 to H2) furnaces permits to separate several fractions. At the end of each separation phase the pressure in the line is measured with a capacitance manometer before analysis of the gas mix ture with a mass spectrometer. Calibration is done periodically using standard gases stored in gauged bottles. The detection limits are 0.5 to 1. X 10-' mot H2O, 0.3 x 10-' mol C02 and about 0 .2 x 10' mol for H2, N2, CO, CH4 and Ar. Further species like organic compounds, S02 and H2S are detected but not determined. In the case of H2O and C02 the reproducibility is better than 4% . The conjunction of vacuum crushing, stepwise heating and size fraction analysis permits to separate components like: dissolved, adsorbed and vesicle trapped. In particular, effects of adsorption have been evaluated: it is a serious problem for , species like CO2 and H2O with finely crushed material. H2 and CO detected after thermal extraction when organic compounds are present in the sample reflect organic decomposition rather than any thermodynamic equilibrium attained upon rock formation .

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Données sur Potassium et Argon (de 1976 à 1984) Dans quelques Echantillons Géochimiques de Reference

Cited by 18 publications

References 8 publications

A new unspiked K‐Ar dating approach using laser fusion on microsamples

A new unspiked K‐Ar dating approach using laser fusion on microsamples

Time-pressure and temperature constraints on the formation of Colombian emeralds; an 40 Ar/ 39 Ar laser microprobe and fluid inclusion study

Manometric and mass spectrometric analysis of fluids in geological meterials.

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