Diffusion, Closure Temperatures and Accessory Mineral Petrogenesis in a High-Temperature Aureole: Refining the Integration of P-T and t

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Connelly/CarlsonEAR-0087564Mineral assemblages in rocks exposed in continental collisional belts (orogens) commonly preserve important information about the high temperatures and pressures they experienced on their respective excursions into the deep crust. Understanding crustal dynamics of these belts requires integration of temperature (T) and pressure (P) and ages (t) to derive P-T-t paths for different parts of an orogen. However, P-T-t paths are not easily defined since independent estimates of P, T and t are based on isotopic and chemical distributions that are dependent on reactions or diffusion that stop at different temperatures. This may leave pressure estimates without corresponding temperature estimates and vice versa, thus precluding definition of real points on the actual P-T path. Estimates of the timing of metamorphism are based on minerals that form in poorly understood reactions and may be reset at temperatures that do not coincide with either P or T estimates. Improved P-T-t paths require refined calibrations of the first-order processes that control elemental and isotopic distributions that are used to define, P, T and t in mineral systems. We will examine elemental and isotopic variations in minerals around a high-temperature (+1000 degrees C) igneous complex of the Nain Plutonic Complex (Labrador, Canada), where pressures were constant and temperatures varied systematically. This work will facilitate calibration of elemental diffusion and relevant mineral reactions as a function of temperature, mineralogy and textural relationships. In turn, this will contribute to our ability to construct more accurate P-T-t paths and thus refine our understanding of the crustal dynamics in collisional orogens.