EGU2020-10696
https://doi.org/10.5194/egusphere-egu2020-10696
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Analysis of Experimentally Zoned Crystals to Investigate The Thermo-Chemical Evolution of Magma Reservoirs

Alessandro Musu1, Luca Caricchi1, Diego Perugini2, Rosa Anna Corsaro3, Francesco Vetere2, and Maurizio Petrelli2
Alessandro Musu et al.
  • 1Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland
  • 2Department of Physics and Geology, University of Perugia, Piazza dell’Università, 1, 06123 Perugia, Italy
  • 3Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo-Sezione di Catania, Catania, Italy

Magma reservoirs are characterized by thermal and chemical gradients producing large variations of the spatial distribution of the physical properties of the magma they contain. Understanding the pre-eruptive thermal, chemical and physical evolution of magma represents an important step to correctly interpret the signs of an impending eruption. In this framework, the chemical zoning of minerals, which provide us a record of these thermal and chemical perturbations, represents an important tool to reconstruct reservoir dynamics. We study the effect of the competition between changing intensive parameters, element diffusion and mineral growth on the chemical zoning of minerals. We grow chemical zoned minerals at the Petro-Volcanology Research Group of the University of Perugia, using tephra from 2002-03 Mt. Etna eruption as starting material. The zonation in minerals is been forced inside a high-temperature furnace by oscillating the temperature under three different conditions: static conditions, using a controlled deformation gradient (concentric cylinder apparatus) and using a chaotic mixing regime (Chaotic Magma Mixing Device – CMMD). We collect major and trace elements distribution maps on a large number of crystals using Electron Probe Micro Analyzer (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), respectively. The data will be analysed using a series of custom built machine learning algorithms to disentangle zoning related to variations of the thermodynamic conditions of crystal growth from the effects of the competition between diffusion and growth. Our data will help deciphering the zoning patterns observed in natural crystals, improve our understanding of magma reservoir dynamics and help the interpretation of monitoring signals in the period preceding a volcanic eruption.

How to cite: Musu, A., Caricchi, L., Perugini, D., Corsaro, R. A., Vetere, F., and Petrelli, M.: Analysis of Experimentally Zoned Crystals to Investigate The Thermo-Chemical Evolution of Magma Reservoirs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10696, https://doi.org/10.5194/egusphere-egu2020-10696, 2020

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Presentation version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-10696, Adrian Hornby, 05 May 2020

    Great presentation, thank you Alessandro!

    I have seen similar boundary layers in intermediate lava, and they appear to have promoted heterogeneous nucleation of Fe-rich nanolites along the rims of plagioclase microlites. Due to their similar BSE intensity to the groundmass glass, plagioclase crystals can be best observed by a ring of surrounding bright nanolites in BSE images. I would be happy to share some images if you contact me directly.

    I am facing the same issue in constraining the composition of the boundary layers. I wanted to point to the brilliant work done by E Bruce Watson and Thomas Mueller on characterising the conditions for boundary layer development, and correlations between crystal-rim and boundary layer composition (Watson, E. B., & Müller, T. (2009). Non-equilibrium isotopic and elemental fractionation during diffusion-controlled crystal growth under static and dynamic conditions. Chemical Geology, 267(3–4), 111–124. https://doi.org/10.1016/j.chemgeo.2008.10.036), which might be useful in experiment design and indirect techniques to estimate the boundary layer chemistry. TEM analysis could be a big help, but it is not always easy to access...

    So my question: do you have any thoughts on how boundary layers (or consequent heterogenous nucleation) might affect magma rheology and eruption dynamics?

    Thanks again,

    Adrian

    • CC2: Reply to CC1, Thomas Griffiths, 05 May 2020

      Dear Adrian, I am not Alessandro but I would be very interested in the pictures you describe! I am studying clustering of magnetite on Cpx dendrites and we suspect the same mechanism may lead to their formation and explain both clustering and resulting crystal orientation relationships. The boundary layer is no longer visible in the experiments we studied, but it was definitely there originally and hopefully with shorter runs we will see it. I would be very happy if you would check out our contribution, https://meetingorganizer.copernicus.org/EGU2020/EGU2020-10336.html

      And I would also be interested in the answer to Adrian's last question!

      best regards, Tom Griffiths, Uni Vienna (Austria)

      • CC3: Reply to CC2, Thomas Griffiths, 05 May 2020

        my email: th.griffiths@univie.ac.at

    • AC1: Reply to CC1, Alessandro Musu, 05 May 2020

      Thank you very much Adrian, for your comment and your advice!

      I would be happy to see and discuss your images.

      Thanks for your question as well, I have not yet considered the effect of boundary layers on rheology, and I think that this is a good point!

      What I think is that the boundary layer around crystals can be also seen as a surrounding film of a fluid, having different rheological properties compered to the melt, and this might influence and maybe facilitate the mobility of melt between crystals; in that way this process can reduce the impact of crystal content on the magma viscosity. But these are only speculations for the moment. I think that can be interesting to perform some experiment also in that direction.

      Thank you again,

      Alessandro

  • CC4: Comment on EGU2020-10696, Thomas Griffiths, 05 May 2020

    Luca commented in the chat that it is interesting/surprising that in the Pontesilli et al experiments I was presenting the boundary layer around Cpx is invisible after annealing of a few hours or less, whereas here the boundary layer may persist for 48 hours, unless it is only forming on quenching.

    The phases and layer compositions are different, so I don't have an opinion either way, and I also did not do the experiments, just wanted to post the link to Alessio & Matteo's paper so you can look yourselves at the calculations they did about the boundary layer, maybe something in there might help explain the difference (or non-difference). The link is: http://www.sciencedirect.com/science/article/pii/S0009254119300567

    I certainly wonder whether the fact that your layer might have evolved enough to become an immiscible second liquid phase might be enough to allow it to persist for a long time despite annealing. If so, you might be getting a sort of "zone refining" effect, where impurities/incompatibles keep building up in the liquid layer pushed in front of the crystal.

    best regards,

    Tom Griffiths, University of Vienna

    • AC2: Reply to CC4, Alessandro Musu, 09 May 2020

      Thank you very much for the comment and for the paper, I found it really interesting.

      Yes, I think that there is the possibility that our boundary layer has been formed during quenching. The two experiments present different setup and different starting conditions. What it is absolutely necessary now is to try to better constrain the composition of the layer and perform more analysis in order to understand when the layer formed, and if in our condition we have already reached the immiscibility.

      Thank you again,

      Alessandro Musu