Villa, Igor Maria (2013). Ar diffusion in K-feldspar: present and absent. In: 40Ar/39Ar Dating: from Geochronology to Thermochronology, from Archaeology to Planetary Sciences. Geological society of London: special publications: Vol. 378 (pp. 107-116). London: Geological Society London 10.1144/SP378.4
Full text not available from this repository.The mechanisms of Ar release from K-feldspar samples in laboratory experiments and during their geological history are assessed here. Modern petrology clearly established that the chemical and isotopic record of minerals is normally dominated by aqueous recrystallization. The laboratory critique is trickier, which explains why so many conflicting approaches have been able to survive long past their expiration date. Current models are evaluated for self-consistency; especially Arrhenian non-linearity leads to paradoxes. The models’ testable geological predictions suggest that temperature-based downslope extrapolations often overestimate observed geological Ar mobility substantially.
An updated interpretation is based on the unrelatedness of geological behaviour to laboratory experiments. The isotopic record of K-feldspar in geological samples is not a unique function of temperature, as recrystallisation promoted by aqueous fluids is the predominant mechanism controlling isotope transport. K-feldspar should therefore be viewed as a hygrochronometer.
Laboratory degassing proceeds from structural rearrangements and phase transitions such as are observed in situ at high temperature in Na and Pb feldspars. These effects violate the mathematics of an inert Fick’s Law matrix and preclude downslope extrapolation. The similar upward-concave, non-linear shapes of Arrhenius trajectories of many silicates, hydrous and anhydrous, are likely common manifestations of structural rearrangements in silicate structures.
Item Type: |
Book Section (Book Chapter) |
|---|---|
Division/Institute: |
08 Faculty of Science > Institute of Geological Sciences |
UniBE Contributor: |
Villa, Igor Maria |
Subjects: |
500 Science > 550 Earth sciences & geology |
Series: |
Geological society of London: special publications |
Publisher: |
Geological Society London |
Language: |
English |
Submitter: |
Igor Maria Villa-Toscani |
Date Deposited: |
14 Aug 2014 10:32 |
Last Modified: |
05 Dec 2022 14:31 |
Publisher DOI: |
10.1144/SP378.4 |
URI: |
https://boris.unibe.ch/id/eprint/46915 |
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