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Petrologic imaging of magmatic reservoirs: some improvements to clinopyroxene and amphibole barometry

Etienne Médard 1, Carole Berthod2, Aurélie Altermatt3, Bixente Guyon1, Pablo Samaniego1, Jean-Luc Le Pennec4, Jean-Luc Devidal1

  • Affiliations: 1Laboratoire Magmas et Volcans, Université Clermont Auvergne, Clermont-Ferrand, France; 2Observatoire Volcanologique et Sismologique de Guadeloupe, Institut de Physique du Globe de Paris, Paris, France; 3Institut für Mineralogie, Leibniz Universität Hannover, Hannover, Germany; 4Geo-Ocean, Université de Bretagne Occidentale, Plouzané, France

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 50

  • Programme No: 1.7.37

  • Theme 1 > Session 7

Abstract

Barometry based on mineral phases is potentially a powerful tool to investigate the feeding system of active volcanic edifices, however, this approach is severely limited by large uncertainties in existing models (often in the range of 5-10 km depending on models). In this presentation, we will raise a series of key issues that need to be addressed to move forward with mineral barometry: the importance of the calibration database, the difference between accuracy and precision and their use, and the needed feedback between modeling and experimental petrology. We will present two ongoing developments based on amphibole and clinopyroxene barometry, respectively. Barometry based on Al-in amphibole is critically dependent on the associated phases. For amphiboles in equilibrium with plagioclase and biotite in calk-alkaline to mildly alkaline rocks, we calibrated a new barometer (Médard and Le Pennec 2022) with a precision up to 0.8 km and an accuracy around 3 km (depths calculated assuming a granitic crust with a density of 2700 kg.m-3). Precision is sufficiently low so that the barometer could be used to investigate the shape of magma reservoirs, giving us a real shot at true petrologic imaging, at least for large silicic eruptions. Clinopyroxene-based barometry can be significantly improved by combining existing calibrations with accurate high-pressure high-temperature experiments run on the composition of interest. Ongoing tests on mildly-alkaline basalts from the Chaîne des Puys volcanic field suggest that in a well-studied volcanic system, accuracy could be decreased to around 3.5 km with a precision of about 0.5 km.