A Bayesian approach to the deconvolution of 40Ar/39Ar data from mineral mixtures

Carter, John N.; Tremblay, Marissa M.; Mark, Darren F.

doi:10.1016/j.chemgeo.2020.119784

Cited by 3 publications

(1 citation statement)

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“…In all cases, the method has yielded consistent results. Other statistical approaches offer promise (e.g., Carter et al, 2020). These developments offer the potential to broaden and diversify theory and practice in argon geochronology.…”

Section: Dealing With the Natural Complexity Of An Age Spectrummentioning

confidence: 99%

Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

Muston¹,

Forster

Vasegh

et al. 2021

Preprint

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Abstract. The Martabe deposits in Sumatra, Indonesia formed in a shallow crustal epithermal environment (200–350 °C) associated with mafic intrusions, usually recognised in domes, adjacent to an active right-lateral wrench system. Ten samples containing alunite were collected for high-resolution geochronology, to determine if overprinting fluid systems could be recognised by dating alunite separates. The heating time for each step was chosen to ensure reasonable uniformity in terms of the incremental percentage of 39Ar gas release during each of many steps, allowing age spectra to be analysed using the method of asymptotes and limits. Several distinct growth events could be recognised. In addition, each sample was subjected to ultra-high-vacuum (UHV) furnace step-heating, and 39Ar diffusion experiments conducted at the same time as 40Ar/39Ar geochronology, to determine the argon retentivity of the mineral grains being analysed. The heating schedule ensured Arrhenius data uniformly populated the inverse temperature axis, with sufficient detail to allow the application of the Fundamental Asymmetry Principle (FAP) during analysis of the Arrhenius spectrum. Results show activation energies between 370–660 kJ/mol. Application of Dodson’s recursion determines that closure temperatures would range from 400–560 °C for a cooling rate of 20 °C/Ma, which is higher than any possible temperature to be expected in the natural system. This gives confidence that the ages represent growth during periods of active fluid movement and alteration, since the deposit formed at temperatures < 200 °C at a depth of < 2 km. We conclude that gold in the Purnama pit was the result of fluid rock interactions during very short-lived mineral growth episodes at ~ 2.25 and ~2.00 Ma.

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Section: Dealing With the Natural Complexity Of An Age Spectrummentioning

confidence: 99%

Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

Muston¹,

Forster

Vasegh

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

Evidence against a Late Heavy Bombardment event on Vesta

Cartwright

Hodges

2022

Earth and Planetary Science Letters

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Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

Muston¹,

Forster

Vasegh

et al. 2023

Geochronology

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Abstract. The Martabe gold deposits in Sumatra formed in a shallow crustal epithermal environment associated with intermediate mafic intrusions adjacent to an active right-lateral wrench system. Gas/fluid temperatures reached 200–350 ∘C. The structural geology suggests episodic switches in stress orientations during a Plio-Pleistocene seismotectonic evolution. Different mineralisation events may have been associated with oscillations in this earthquake cycle, so samples containing alunite were collected for 40Ar / 39Ar geochronology to constrain the timing. 39Ar diffusion experiments were performed to constrain variation in argon retentivity. The age spectra were produced by incremental step-heating with heating times chosen so similar percentages of 39Ar gas release occurred during as many steps as possible. This ensured the detail necessary for analysis of the complex morphology of these spectra by applying the method of asymptotes and limits, which enabled recognition of different growth events of alunite in overprinting fluid systems. It was possible to provide estimates as to the frequency of individual events and their duration. The heating schedule also ensured that Arrhenius data populated the inverse temperature axis with sufficient detail to allow modelling. Activation energies were between 370–660 kJ mol−1. Application of Dodson's recursion determined closure temperatures that range from 400–560 ∘C for a cooling rate of 100 ∘C Ma−1. Such estimates are higher than any temperature to be expected in the natural system, giving confidence that the ages represent the timing of growth during periods of active fluid movement and alteration: a hypothesis confirmed by modelling age spectra using the MacArgon program. We conclude that gold in the Purnama pit resulted from overprinting fluid rock interactions during very short mineralisation episodes at ∼2.25 and ∼2.00 Ma.

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A Bayesian approach to the deconvolution of 40Ar/39Ar data from mineral mixtures

Cited by 3 publications

References 78 publications

Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

Evidence against a Late Heavy Bombardment event on Vesta

Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

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