Collaborative Research: Argon Retentivity and Closure Temperature in Micas and Amphiboles

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9614822 Dahl This project involves a collaborative, multi-faceted, and multi-disciplinary investigation of compositional and other factors governing Ar retention, Ar closure temperature, and 40Ar/39Ar cooling ages in natural amphiboles and micas. The fundamental research objectives are to: (1) determine the compositional dependence of Ar retentivity within dioctahedral and trioctahedral micas and common amphiboles; (2) examine the role of grain boundaries and sub-grain domains on Ar retentivity; (3) examine the diffusion geometry or anisotropy of Ar in these minerals; (4) test rigorously the ionic-porosity model for Ar retention, and secondarily for Sr and Ca; (5) refine our basic understanding of the crystallographic factors influencing Ar transport and closure temperatures, and (6) add to existing knowledge of cooling history in selected orogenic terranes. The field aspect of the proposed work will be focussed in the Adirondack Mountains, NY, and the Black Hills, SD.