Grain-size relationship evidence

Farley, 2000 Reiners and Farley, 1999, 2001), but this relationship breaks down in samples subjected to intensive ductile or brittle deformation (e.g., Amaud and Eide, 2000 Kramar et al, 2001 Mulch et al, 2002). In general, it seems prudent to assume that a is related to the physical grain size when applying Equations (17) and (19) unless samples show textural evidence for the extensive development of subgrain boundaries that may act as fast diffusion pathways, or— in the case of K-feldspar— show direct evidence of the existence of multiple diffusion domains during incremental heating experiments. 

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