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Dates, Rates, Ages and Stages: New developments in determining metamorphic timescales

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The incorporation of naturally-decaying radioactive elements into different minerals allows geologists to use them as geological ‘clocks’. The accurate and precise determination of the ages of these minerals, and different crystallisation zones within them, allows the timing, rates and timescales of tectonic processes to be determined. However in order to reliably interpret ‘dates’ as geologically meaningful ‘ages’, the crystallisation reactions of these minerals need firstly to be determined, and secondly to be linked to the reaction history of the major rock-forming minerals. These latter minerals preserve information about the pressure, temperature and transport history. Linking the crystallisation history of the accessory to the major phases is particularly important in metamorphic rocks, as these commonly record complex histories.

Recent advances in in-situ analysis, such as by laser ablation or secondary ion sputtering, allow increasingly precise information to be yielded from smaller volumes of material. Furthermore, trace element concentrations and ratios act as ‘fingerprints’ that allow the formation and dissolution of the geochronometers to be linked to the evolution recorded by the main rock-forming minerals

This talk will focus on two recent developments in linking ‘age to stage’: firstly determining the crystallisation history of the high grade metamorphic rocks that form the core of the Himalayan mountain belt, and secondly unravelling the exhumation history recorded by Ar/Ar ages from the Western Gneiss Region in Norway. Both regions provide a rich mine of information about the tectonic processes operating deep within mountain belts, allowing information from the present to be compared to the past.

Clare Warren is a NERC Advanced Postdoctoral Fellow at the Open University, UK. She gained her BA and DPhil at Oxford, and has been at the OU since 2008. She has published >25 papers on the formation and evolution of mountain belts, using geochronological, petrogenetic modelling and geodynamic modelling tools. Her research focuses on resolving the rates and timescales of metamorphic processes during the early (high pressure) and middle (high temperature) stages of continental collision. At the moment she is trying to improve techniques to link metamorphic U-Pb and Ar/Ar ‘age’ to metamorphic ‘stage’ using trace element reaction fingerprinting techniques.

This talk is part of the Sedgwick Club talks series.

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