| Popis: |
New data from a gem-quality feldspar from Itrongay, Madagascar, record naturally occurring 40 Ar/ 39 Arageprofileswhichcanbenumericallymodelledbyinvokinga singlediffusion mechanism and show that microtexturally simple crystals are capable of recording complex thermal histories. We present the longest directly measured, naturally produced 40 Ar*-closure pro- files from a single, homogeneous orthoclase feldspar. These data appear to confirm the assumption thatlaboratoryderiveddiffusionparametersarevalidinnatureandovergeologicaltimescales.Dif- fusion 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. Supplementary material: Ar-isotope data, standards and constants used in calculations and irradiation parameters are available at http://www.geolsoc.org.uk/SUP18720 Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. |
