EGU2020-20063, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-20063
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Investigating H2O contents in clinopyroxene from explosive versus effusive eruption products from Merapi volcano, Indonesia

Dimitrios Dimitriou1, Valentin Troll1, Franz Weis1,2, Nadhirah Seraphine1, Frances Deegan1, Henrik Skogby2, Hanik Humaida3, and Ralf Gertisser4
Dimitrios Dimitriou et al.
  • 1Department of Earth Sciences, Uppsala University, Uppsala, Sweden
  • 2Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
  • 3BPPTK (Balai Penvelidikan dan Pengembangan Teknologi Kegunungapian), Yogyakarta, Indonesia
  • 4School of Geography, Geology and the Environment, Keele University, Keele, United Kingdom

The 2010 eruption of Merapi produced pyroclastic deposits and lava flows that are compositionally very similar, raising the question as to the underlying reason of the differences in eruptive styles between the various phases of the 2010 eruptive events. To test whether primary magmatic volatile content is the reason for the different eruption styles, we analyzed magmatic water contents in nominally anhydrous clinopyroxene crystals contained in lava and ash from the 2010 eruptive events. We utilized two analytical approaches: (i) Fourier-transform infrared spectroscopy (FTIR) analysis of fresh clinopyroxene from the ash and lava samples and (ii) FTIR analysis of clinopyroxene both prior to and after experimental re-hydration. By employing calculated partition coefficients, we determined the magmatic water content of the magma from which the various crystals grew. The magmatic water content determined from the unmodified clinopyroxenes from lava samples yield a range of 0.35 wt.% to 2.02 wt.% H2O, whereas magmatic water contents determined from untreated clinopyroxene contained in the ash samples range between 0.04 and 3.25 wt.%, with two outliers at 4.62 and 5.19 and wt.%, respectively. In contrast, for the rehydrated crystals the range for lava derived clinopyroxene crystals is between 1.94 and 2.19 wt.% and for ash between 1.74 and 2.66 wt.%, with two crystals at extreme values of 0.85 and 3.20 wt.%. We interpret these results to indicate that crystals from different populations are present in the 2010 eruptive products, with the dominant group reflecting relatively low magmatic H2O contents (around 2 wt.%) due to storage in shallow magma reservoirs and pockets at high levels within the Merapi plumbing systems (e.g. top 3 km). The overall higher H2O range and the occasionally more extreme values recorded in clinopyroxenes from ash deposits may then represent the presence of a crystal population that last equilibrated at deeper levels and at higher water contents, i.e. these crystals derive from the replenishing magma that activated the shallow portion of the plumbing system during the 2010 events. While this is work in progress, our results so far seem to suggest that the pyroclastic deposits of the 2010 Merapi eruption may contain a higher fraction of clinopyroxene derived from ‘deeper magma’ with higher H2O contents then what we have detected in associated lavas.

How to cite: Dimitriou, D., Troll, V., Weis, F., Seraphine, N., Deegan, F., Skogby, H., Humaida, H., and Gertisser, R.: Investigating H2O contents in clinopyroxene from explosive versus effusive eruption products from Merapi volcano, Indonesia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20063, https://doi.org/10.5194/egusphere-egu2020-20063, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 03 May 2020
  • CC1: Comment on EGU2020-20063, Gerhard Wörner, 04 May 2020

    Hi,

    can you compare the degassing and non-degassing depths to any other barometry approach ?

    Fluid inclusions ? Melt inclusions ? even Cpx barometry ?

    I do not recall: what are the time scales of the cpx H2O-degassing... are these in line with other diffusion-modelling or is water too fast, e.g. compared to Fe/Mg in Ol.

    If H2O is indeed very fast, what is the relevance of the shallow degassing level: storage or just degassing kinetics during slow but continuous ascent.

    Nice... !

    Your study gives me all kinds of ideas of where to go and check using the same approach.. !

    Gerhard

    • AC1: Reply to CC1, Frances Deegan, 04 May 2020

      Indeed, our data seem consistent with MI data from Preece et al. (2016 I think). We can send a MSc thesis of preliminary results should you be interested. Happy to help with analysis if you need it! 

      Thanks so much for your interest!

      Frances and Val.

       

      • AC2: Reply to AC1, Dimitrios Dimitriou, 04 May 2020

        It is Preece et al 2014 as a matter of fact. Also I would like to add Costa et al 2013, who used Amphibole thermobarometry and whose results also seem to match ours. 

  • CC2: Comment on EGU2020-20063, Konstantinos Thomaidis, 05 May 2020

    Hello Dimitris and thank you for your presentation. I have a question regarding your  FTIR analyses. How are your spectra look like? Do you see any difference between the OH bands signatures for the different samples (ash, lava)? Cheers! :-) 

    • AC4: Reply to CC2, Valentin Troll, 06 May 2020

      Tack Konstantinos! Hope you are well? Lets have a chat next week perhaps...we can aim for a video chat perhps as I love to see you again and also chat about research to write up etc. Wonderful to hear from you !!! val

    • AC5: Reply to CC2, Dimitrios Dimitriou, 07 May 2020

      Thank you for your comment Konstantinos. The spectra of the lava samples are usually not as strong as the ash samples, due to the, usually, less H2O in the crystals 

  • AC3: Comment on EGU2020-20063, Valentin Troll, 06 May 2020

    Tack Konstantinos! Hope you are well? Lets have a chat next week perhaps...we can aim for a video chat perhps as I love to see you again and also chat about research to write up etc. Wonderful to hear from you !!! val