Publication Date:
2014-05-11
Description:
40 Ar/ 39 Ar dating of young (〈1 Ma) and/or low potassium samples requires degassing of large amounts of material either by a laser or a furnace. A furnace excels in precise and reproducible temperature control and in providing a homogeneous temperature distribution even for relatively large samples amounts. For most systems, however, the degassed mineral or whole-rock residues remain in the crucible after measurement. This reduces the thermal conductivity and increases the blank levels and baking times. To mitigate these problems, we combined a mechanical sample transfer system with a low volume (~90 ml) high-temperature cell. The system operates under ultra-high vacuum and uses Mo-crucibles, in which up to 1000 mg of sample is transferred into the furnace and taken out after degassing. The system has short baking times (20-30 min), highly reproducible heating conditions and an overall low blank level due to the absence of silicate (glassy) sample residue in the main crucible of the furnace. The system interconnects through a gas purification line with a low volume, high sensitivity multi-collector ARGUS noble gas mass spectrometer. Intraday reproducibility of 40 Ar/ 36 Ar ratios measured on air aliquots of 〉5×10 -16 mol 36 Ar is better than 0.5 – 1.0 ‰ (1σ, n=4–8). We illustrate the system performance by 40 Ar/ 39 Ar dating of whole-rock samples and mineral separates from the Oman ophiolite as well as from the Siebengebirge, Heldburg, and Rhön volcanic provinces in Central Germany.
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
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