Advances in
            <sup>40</sup>
            Ar/
            <sup>39</sup>
            Ar dating: from archaeology to planetary sciences – introduction

Jourdan, Fred; Mark, Darren F.; Vérati, Chrystèle

doi:10.1144/sp378.24

Cited by 16 publications

(6 citation statements)

References 58 publications

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“…The uncertainties on the 40 Ar*/ 39 Ar ratios of the monitor are included in the calculation of the integrated and plateau age uncertainties, but the uncertainties on the age of the monitor and on the decay constant are not (internal errors only). Fully propagated uncertainties including uncertainty on the R ‐value of the monitor WA1ms against FCs (Jourdan, Mark, & Verati, ) and uncertainty of the decay constants using a Monte Carlo error propagation approach (Renne, Mundil, Balco, Min, & Ludwig, ) results in an increase in uncertainty of ± c . 1 Ma.…”

Section: Methodsmentioning

confidence: 99%

Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Blereau

Clark

Jourdan

et al. 2019

Journal Metamorphic Geology

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Here, we present results of the first 40Ar/39Ar dating of osumilite, a high‐T mineral that occurs in some volcanic and high‐grade metamorphic rocks. The metamorphic osumilite studied here is from a metapelitic rock within the Rogaland–Vest Agder Sector, Norway, an area that experienced regional granulite facies metamorphism and subsequent contact metamorphism between 1,100 Ma and 850 Ma. The large grain size (~1 cm) of osumilite in the studied rock, which preserves a nominally anhydrous assemblage, increases the potential for large portions of individual grains to have remained essentially unaffected by the effects of diffusive argon loss, potentially preserving prograde ages. Step‐heating diffusion experiments yielded a maximum activation energy of ~461 kJ/mol and a pre‐exponential factor of ~8.34 × 108 cm2/s for Ar diffusion in osumilite. These parameters correspond to a relatively high closure temperature of ~620°C for a cooling rate of 10°C/Ma in an osumilite crystal with a 175 µm radius. Fragments of osumilite separated from the sample preserve a range of ages between c. 1,070 and 860 Ma. The oldest ages are inferred to date the growth of coarse‐grained osumilite during prograde granulite facies regional metamorphism, which pre‐date contact metamorphism that has historically been ascribed to the growth of osumilite in the region. The majority of fragments record ages between c. 920 and 860 Ma, inferred to reflect the growth of osumilite and/or diffusive argon loss during contact metamorphism. The retention of old 40Ar/39Ar dates was facilitated by the low diffusivity of Ar in osumilite (i.e. a closed system), large grain sizes, and anhydrous metamorphic conditions. The ability to date osumilite with the 40Ar/39Ar method provides a valuable new thermochronometer that may constrain the timing and duration of high‐T magmatic and metamorphic events.

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Section: Methodsmentioning

confidence: 99%

Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Blereau

Clark

Jourdan

et al. 2019

Journal Metamorphic Geology

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“…The energy of other infrared lasers (the 1064 nm Nd:YAG and various diode lasers) is much less effectively absorbed by transparent to subtransparent minerals, including muscovite and feldspar, which may require micro-encapsulation in a metal such as niobium (e.g., Jourdan et al, 2014). Both 1064 nm Nd:YAG lasers and infrared diode lasers are typically used to extract Ar at lower irradiances by heating or melting by expanding the beam focal point or lowering the laser power.…”

Section: Laser Technologiesmentioning

confidence: 99%

Interpreting and reporting 40Ar/39Ar geochronologic data

et al. 2020

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The 40Ar/39Ar dating method is among the most versatile of geochronometers, having the potential to date a broad variety of K-bearing materials spanning from the time of Earth’s formation into the historical realm. Measurements using modern noble-gas mass spectrometers are now producing 40Ar/39Ar dates with analytical uncertainties of ∼0.1%, thereby providing precise time constraints for a wide range of geologic and extraterrestrial processes. Analyses of increasingly smaller subsamples have revealed age dispersion in many materials, including some minerals used as neutron fluence monitors. Accordingly, interpretive strategies are evolving to address observed dispersion in dates from a single sample. Moreover, inferring a geologically meaningful “age” from a measured “date” or set of dates is dependent on the geological problem being addressed and the salient assumptions associated with each set of data. We highlight requirements for collateral information that will better constrain the interpretation of 40Ar/39Ar data sets, including those associated with single-crystal fusion analyses, incremental heating experiments, and in situ analyses of microsampled domains. To ensure the utility and viability of published results, we emphasize previous recommendations for reporting 40Ar/39Ar data and the related essential metadata, with the amendment that data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR) by both humans and computers. Our examples provide guidance for the presentation and interpretation of 40Ar/39Ar dates to maximize their interdisciplinary usage, reproducibility, and longevity.

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“…Indeed, many of the common metamorphic phases such as biotite, muscovite, feldspar, and amphibole can be dated by the 40 Ar/ 39 Ar method; however, it is well acknowledged that this chronometer is highly sensitive to any late thermal perturbation, thus the radiometric ages obtained by this method may represent cooling ages or "re-opening" ages rather than genuine crystallization age of the dated minerals (see Jourdan et al 2014 for a recent review). Zircon is also a common accessory phase used for U-Pb geochronology.…”

Section: Introductionmentioning

confidence: 99%

Monazite U–Th–Pb EPMA and zircon U–Pb SIMS chronological constraints on the tectonic, metamorphic, and thermal events in the inner part of the Variscan orogen, example from the Sioule series, French Massif Central

Couto

Faure

Augier

et al. 2015

Int J Earth Sci (Geol Rundsch)

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International audienceIn the northern Variscan French Massif Central, the Sioule metamorphic series exposes from top to bottom the tectonic superposition of the Upper Gneiss Unit (UGU), Lower Gneiss Unit (LGU), and Para-autochthonous Unit (PAU). The nappe stacking developed throughout two prograde syn-metamorphic events: D1 is a top-to-the-SW shearing coeval with a probable Devonian migmatization and D2 is a top-to-the-NW shearing event. Both events were completed before the unconformable deposition of the undeformed and unmetamorphosed “Tufs anthracifères” formation, dated at ca 330 Ma (Late Visean). Furthermore, the UGU experienced a high-pressure metamorphism ascribed to a D0 event during which eclogite or granulite crystallized in several parts of the UGU. Monazite U–Th–Pb and zircon U–Pb SIMS datings were carried out in order to constrain the ages of these D0, D1, and D2 tectono-metamorphic events. These new geochronological results are placed in a P–T-t diagram constructed for the UGU, LGU, and PAU. Monazite sampled in UGU, LGU, and PAU rocks yields similar 365–350 Ma ages consistent with the D2 event dated in other places of the French Massif Central. A zoned monazite grain from a granulitic paragneiss yields 416 ± 15 and 362 ± 14 Ma ages interpreted as those of the D0 and D2 events, respectively. Zircon from the same granulitic paragneiss yields SIMS ages at 343 ± 2 and 328 ± 2 Ma that are interpreted as recrystallization processes associated with post-thickening thermal events, possibly recording the onset of orogenic collapse of the Northern Massif Central. It is worth to note that neither monazite nor zircon recorded the D1 event

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Advances in ⁴⁰ Ar/ ³⁹ Ar dating: from archaeology to planetary sciences – introduction

Cited by 16 publications

References 58 publications

Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Interpreting and reporting 40Ar/39Ar geochronologic data

Monazite U–Th–Pb EPMA and zircon U–Pb SIMS chronological constraints on the tectonic, metamorphic, and thermal events in the inner part of the Variscan orogen, example from the Sioule series, French Massif Central

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Advances in 40 Ar/ 39 Ar dating: from archaeology to planetary sciences – introduction

Cited by 16 publications

References 58 publications

Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Interpreting and reporting 40Ar/39Ar geochronologic data

Monazite U–Th–Pb EPMA and zircon U–Pb SIMS chronological constraints on the tectonic, metamorphic, and thermal events in the inner part of the Variscan orogen, example from the Sioule series, French Massif Central

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Advances in ⁴⁰ Ar/ ³⁹ Ar dating: from archaeology to planetary sciences – introduction