An Automated System for Measuring In Situ K–Ar Ages

Abstract

A completely automated system for measuring in situ K-Ar ages using laser ablation for argon extraction and potassium measurement, and mass spectrometry for argon determination is described. The system consists of a laser system, an optical spectrometer, a vacuum line, a noble gas mass spectrometer and control software. The automated prototype was designed with ease of use in mind, specifically planned for dating many samples at low cost and reasonable precision. This instrumentation can perform one hundred K-Ar analyses every 24 h with the current setup, including blanks, reference materials and unknowns. Measurement results for the reference materials HDB-1 biotite, GL-O glauconite, LP-6 biotite, Mica-Mg phlogopite, Alder Creek sanidine and two tektites (moldavite and indochinite) are presented. It is shown that very different sample matrices require specific calibrations. Uncomplicated sample preparation, fast analytical times and uncertainties typically below 5% (1 standard deviation), depending on the age and potassium content, are the hallmarks of the system, which is suitable for many exploratory geology applications (e.g. geological mapping, mineral provenance and dating of drill cores).

Testing Nano‐Powder and Fused‐Glass Mineral Reference Materials for In SituRb‐Sr Dating of Glauconite, Phlogopite, Biotite and Feldspar via LA‐ICP‐MS/MS

“…2017, Olierook et al . 2020, Solé 2021), and also within the range reported recently by Jegal et al . (2022) (see also Table 1).…”

“…2006, Derkowski et al . 2009), the latter also confirmed by a new in situ K‐Ar technique that yielded 94 ± 1 Ma (Solé 2021). However, GL‐O powders and grains investigated in Odin et al .…”

“…However, these ages are older than the Rb‐Sr and K‐Ar ages of 'bulk' GL‐O constrained at 91.7 ± 7.1 Ma (recalculated from Odin et al . (1982)) and 94 ± 1 Ma (Solé 2021), respectively. This could be related to matrix effects between GL‐O grains and Mica‐Mg‐NP (i.e., differences in chemical and ablation properties), as this effect could impact the accuracy of the in situ Rb‐Sr age by up to 8% (Redaa et al .…”

“…2022). In addition, novel in situ K‐Ar dating of Mica‐Mg yielded an age of 525 ± 10 Ma (Solé 2021). The variations in the reported absolute ratios suggest some heterogeneity between batches and/or between pressed NP pellets, however, the age is likely to be homogeneous.…”

Atomic spectrometry update – a review of advances in environmental analysis

“…In studies of other geochronometers , a fully automated system was developed 263 for in situ measurements of K–Ar ages. The automated prototype consisted of a laser system, an optical spectrometer, a vacuum line, a noble gas mass spectrometer and control software and was designed to date many samples at low cost and with a precision suitable for applications in exploration geology.…”