Suitability of volcanic glasses with different compositions and evolution histories to gain paleointensity data

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High quality paleointensity data is essential to many geoscientific problems like the state of the magnetic field during long lasting magnetic quiet zones (so-called superchrons) or dating of archeological artefacts. However, obtaining them is very time-consuming and success rates of the experiments are low. It has been suggested that usage of ideal materials like volcanic glass can improve both quality and quantity of intensity data, but questions regarding the remanence carriers, the origin of the remanence, the influence of composition, cooling rate, hydration and devitrification are yet to be answered completely. Here we propose to combine a study on synthesized glasses (with known history: composition, oxygen fugacity, magnetic field) with a study on natural glasses of different compositions. While the synthetic glasses will help to answer questions regarding the remanence carriers and the origin of the remanence, the second part of the project on differentiated volcanic glasses, i. e. obsidians, from different geological settings (e.g. mid ocean ridge, continental collision zone), with varying evolution histories (e.g. aerial, subglacial; hydration, perlitization, devitirfication) and diverse compositions (e.g. rhyolite, phonolite) will help to understand the influences of these different circumstances. The required obsidian samples are either already available (from earlier field trips to Armenia and Iceland) or will be taken on a field trip to Iceland. Additionally basaltic glasses of both submarine and subglacial origin will be investigated to also check for ageing effects. We will take a combined rock magnetic, paleomagnetic and volcanological approach to analyze the various samples: Remanence carriers and magnetic properties, paleodirections and -intensities, glass transition temperatures, natural cooling rates and volatile contents will be determined. The additional information from experiments will enable us to correct the paleointensity data for influences like cooling rate dependency or hydration effects. The paleomagnetic data will be included in paleo- and/or archeomagnetic data bases and our gained knowledge about the significance of different evolution histories of the glasses will be used to develop a catalogue of suitability criteria for paleointensity samples and if necessary to propose adaptations to the so far used paleointensity methods.