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Journal of the Geological Society; 2007; v. 164; issue.5; p. 941-944;
DOI: 10.1144/0016-76492006-180
© 2007 Geological Society of London

Short Communication

Understanding K-feldspar 40Ar/39Ar data: reconciling models, methods and microtextures

Sandra McLaren1,2, W.James Dunlap1 & Roger Powell2

1 1Research School of Earth Sciences, Australian National University, Acton, ACT 0200, Australia
2 2School of Earth Sciences, University of Melbourne, Melbourne, Vic. 3010, Australia (e-mail: mclarens{at}unimelb.edu.au)

Several descriptions of argon diffusion in K-feldspar have been developed, including the quantitative multiple-diffusion-domain (MDD) and multipath models and the qualitative ‘recrystallization’ model. These models remain contentious and the natural range in behaviour remains poorly understood. Feldspars from the Klokken syenite intrusion show a systematic relationship between 40Ar/39Ar age and microtexture suggesting that the loss of argon from different feldspars operates via different mechanisms such that the existing models represent only end-member scenarios. The MDD model can yield reliable thermal history information only for feldspars with pristine microtexture, with this model best viewed as a cipher for the real (but unknown) domain structure in such samples.