Accessory mineral geochemistry in high-T systems

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The Problem: Incompatible trace-element patterns (e.g. REE) are commonly used to model processes in high-temperature geologic systems. However, accessory minerals such may control incompatible trace-element distributions. Thus, understanding the link between the geochemistry of trace-elements and accessory minerals is crucial when applying geochemical modeling to geologic processes. The Objectives: To understand the geochemical influence of accessory minerals on whole-rock patterns in high-temperature geological systems. This will begin by focusing on an initial examination of crustal melt formation and the distribution of various accessory minerals and incompatible trace-elements between the parent rocks of different compositions and the resulting melts. The geochemical evolution of incompatible elements in large magmatic intrusions will also be studied to provide a database of accessory mineral compositions to augment and expand trace-elements databases which currently only exist only for zircon and apatite. This will allow a better comparison of the results of this research with established models for accessory mineral geochemistry and incompatible trace-element behavior in both magmatic and high-temperature metamorphic systems. Methodology: The proposed research will develop and apply micro-analytical techniques to meet the proposed research objectives using existing and newly developed ICP-MS techniques, centered around a new facility at the University du Québec a Chicoutimi. Excellent field study areas at Cap à l'Aigle and St. Fulgence, Québec have been identified and will provide access to a wide variety of parent rock and melt types. Significance: Linking the trace-element geochemical record with accessory mineral distributions will contribute to a significantly better understanding of incompatible element behavior, which in turn will allow more accurate geochemical models for whole-rocks system to be developed. A database of accessory mineral distribution coefficients and concentrations will also be made available.