K-Ar datability of altered rocks: variability of excess Ar in hydrothermal minerals |
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Authors: | Igor M Villa Giorgio Taddeucci |
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Institution: | (1) Istituto di Geocronologia CNR, via Maffi 36, Pisa, Italy;(2) Present address: Isotopengeologie, Erlachstrasse 9A, 3012 Bern, Switzerland |
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Abstract: | 40Ar/39 Ar stepwise heating on one hydrothermal anhydrite and two partly hydrothermalized feldspars from a borehole in Vulcano volcano show that the initial trapped Ar does not have a constant isotopic composition. The constant 40Ar/36Ar ratio of the anhydrite, 306±3, is not a well-defined endmember for the two feldspars, which record a variety of fluid compositions. As the system is young (<100 ka), radiogenic Ar is much less than excess Ar. |
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