Observation of centimetre-scale argon diffusion in alkali feldspars: implications for 40Ar/39Ar thermochronology
Stephanie Flude, Alison M. Halton, Simon P. Kelley, Sarah C. Sherlock, James Schwanethal, Camilla M. Wilkinson, 2014. "Observation of centimetre-scale argon diffusion in alkali feldspars: implications for 40Ar/39Ar thermochronology", Advances in 40Ar/39Ar Dating: From Archaeology to Planetary Sciences, F. Jourdan, D. F. Mark, C. Verati
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New data from a gem-quality feldspar from Itrongay, Madagascar, record naturally occurring 40Ar/39Ar age profiles which can be numerically modelled by invoking a single diffusion mechanism and show that microtexturally simple crystals are capable of recording complex thermal histories. We present the longest directly measured, naturally produced 40Ar*-closure profiles from a single, homogeneous orthoclase feldspar. These data appear to confirm the assumption that laboratory derived diffusion parameters are valid in nature and over geological timescales. Diffusion domains are defined by crystal faces and ancient cracks, thus in gem-quality feldspars the diffusion domain size equates to the physical grain size. The data also illustrate the potential of large, gem-quality feldspars to record detailed thermal histories over tens of millions of years and such samples should be considered for future studies on the slow cooling of continental crust.
Ar-isotope data, standards and constants used in calculations and irradiation parameters are available at http://www.geolsoc.org.uk/SUP18720.
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Advances in 40Ar/39Ar Dating: From Archaeology to Planetary Sciences
Decoding the complete history of Earth and our solar system requires the placing of the scattered pages of Earth history in a precise chronological order, and the 40Ar/39Ar dating technique is one of the most trusted dating techniques to do that. The 40Ar/39Ar method has been in use for more than 40 years, and has constantly evolved since then. The steady improvement of the technique is largely due to a better understanding of the K/Ar system, an appreciation of the subtleties of geological material and a continuous refinement of the analytical tools used for isotope extraction and counting. The 40Ar/39Ar method is also one of the most versatile techniques with countless applications in archaeology, tectonics, structural geology, orogenic processes and provenance studies, ore and petroleum genesis, volcanology, weathering processes and climate, and planetary geology. This volume is the first of its kind and covers methodological developments, modelling, data handling, and direct applications of the 40Ar/39Ar technique.