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Experimental insights into crystal resorption and growth: significance for mush maturation

Martin F. Mangler 1,5, Madeleine C.S. Humphreys1, Alexander A. Iveson1,6, Kari M. Cooper2, Michael A. Clynne3, Amanda Lindoo1,4, Richard A. Brooker4, Fabian B. Wadsworth1

  • Affiliations: 1Department of Earth Sciences, Durham University, Durham, UK 2Department of Earth and Planetary Sciences, University of California, Davis, Davis, USA 3US Geological Survey, Volcano Science Center, California Volcano Observatory,  Moffett Field, USA 4School of Earth Sciences, University of Bristol, Bristol, UK 5School of Ocean and Earth Science, University of Southampton, Southampton, UK 6Pacific Northwest National Laboratory, Richland, USA

  • Presentation type: Talk [Invited]

  • Presentation time: Tuesday 11:15 - 11:30, Room S150

  • Programme No: 3.2.4

  • Theme 3 > Session 2

Abstract

Crystals in volcanic rocks often show internal dissolution surfaces followed by compositionally distinct overgrowths. These resorption-and-overgrowth textures represent sudden changes in magmatic environment (e.g., T, P, X, H2O). However, to date, unambiguous petrological interpretations of resorption-and-overgrowth textures are impossible because they cannot be confidently attributed to specific magmatic processes. To better understand the significance of resorption textures, experiments are needed that isolate the effects of T, P, X fluctuations on crystal dissolution and growth. Here, we present the results of high-P-T resorption experiments isolating the effect of temperature fluctuations on crystal textures. We nucleated, grew, resorbed, and recrystallised plagioclase crystals in a rhyolitic melt, imposing temperature fluctuations typical for plumbing systems in intermediate arc volcanoes (20--40°C) whilst keeping all other variables constant. The experiments reproduce resorption-and-overgrowth features commonly observed in crystals in magmatic rocks and demonstrate that a single temperature spike can introduce significant textural complexity. Moreover, we find that plagioclase dissolution irreversibly reduces crystal aspect ratios, leading to more equant crystal shapes as the amplitude of temperature fluctuations increases. This suggests that crystals stored in magmatic plumbing systems become more equant when exposed to recurring temperature fluctuations. A compilation of plagioclase crystal shapes in Mount St Helens rocks confirms that crystals with dissolution surfaces show systematically more equant shapes than unresorbed crystals. Since equant crystals lock up at higher crystallinities than tabular ones, our findings imply that a mature mush comprising more equant crystals may be more easily eruptible than an immature mush with more tabular crystals.