In situ determination of K–Ar ages from minerals and rocks using simultaneous laser-induced plasma spectroscopy and noble gas mass spectrometry

• A new method to determine the K–Ar age of mineral and rock samples is presented.
• Samples are ablated with a pulsed laser under ultra high vacuum.
• Potassium is measured by optical spectroscopy of the ablation plasma plume.
• Argon, released during ablation, is measured by mass spectrometry.
• The age is calculated using a conversion factor JS and the Ar–Ar equations.

Geochronology is one of the foundations of Earth Sciences and is evolving constantly towards higher reliability and usefulness. Currently, Ar–Ar and U–Pb dating are the geochronological techniques most used. However, the classical K–Ar technique can be modified to measure the age of single minerals or rock sections in situ. This new technique combines the use of laser-induced plasma spectroscopy for the determination of potassium, with noble gas mass spectrometry for the determination of argon, both extracted simultaneously by laser ablation. This work constitutes both a proof-of-concept and a test of this method on 13 samples (53 analyses), with ages in the range 950–70 Ma. Deviations from the conventional K–Ar age are lower than 5% for most samples. The method is characterized by easy analytical procedures and relatively low uncertainty with the equipment used. This method is excellent for exploratory chronology of the earth and extraterrestrial bodies owing to the simple sample preparation and low turnaround time for the analysis.

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