EGU21-14613
https://doi.org/10.5194/egusphere-egu21-14613
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Constraints on the pre-eruption thermal and fO2 conditions in the magma reservoir of Ciomadul (SE Carpathians, Romania) based on Fe-Ti oxide geochemistry

Máté Szemerédi1,2, Katalin Mészáros1, Réka Lukács1, Zoltán Kovács1, and Szabolcs Harangi1,3
Máté Szemerédi et al.
  • 1MTA-ELTE Volcanology Research Group, Budapest, Hungary (szemeredi.mate@gmail.com)
  • 2University of Szeged, Department of Mineralogy, Geochemistry and Petrology, ‘Vulcano’ Petrology and Geochemistry Research Group, Szeged, Hungary
  • 3Eötvös Loránd University, Department of Petrology and Geochemistry, Budapest, Hungary

Ciomadul is the southernmost eruptive centre of the post-collisional Călimani-Gurghiu-Harghita andesitic-dacitic volcanic chain (SE Carpathians, Romania) and represents the latest manifestation of the Neogene to Quaternary volcanism in the Carpathian-Pannonian Region. Ciomadul consists of older, peripheral shoshonitic to dacitic lava domes formed episodically between 1 Ma and 300 ka and a voluminous, central volcanic complex developed within the last 200 ka. Although several lines of evidence (based on petrology, geophysics and gas monitoring) suggest a long-lived magmatic plumbing system holding a potentially active magma storage (“PAMS” volcano) beneath Ciomadul, the pre-eruptive conditions of the upper crustal magma reservoir (including temperature, oxygen fugacity and TiO2 activity) are not completely explored so far. In this study 23 rock samples, representing the whole volcanic activity of Ciomadul in time, were involved. Fe-Ti oxide (magnetite-ilmenite) grains were selected from magnetic heavy minerals, but only a few of the samples contained both magnetite and ilmenite crystals. Equilibrium between Ti-magnetite and ilmenite was tested by their chemical composition (Mg/Mn ratios).

Various geothermobarometer calibrations, including Andersen and Lindsley (1985, 1988) as well as Ghiorso and Evans (2008), were applied to calculate temperature and oxygen fugacity from Fe-Ti oxide compositions. Our results show that, in case of dacitic pyroclastic rocks, temperature values gained by the method of Ghiorso and Evans are significantly lower (640–780 °C) than those obtained by the geothermometers of Andersen and Lindsley (1985, 1988), showing 750–830 and 710–790°C temperatures, respectively. On the other hand, andesitic lava dome rocks of Dealul Mare show higher, 800–900 °C temperature according to all of these methods. The obtained temperature was compared with amphibole-plagioclase thermometry results and this shows a better agreement with the values yielded by the Andersen and Lindsley (1985) Fe-Ti oxide thermometry, particularly for the pumice samples.

In case of oxygen fugacity, the Ghiorso and Evans (2008) and Andersen and Lindsley (1985) methods showed fairly similar values (fO2=0.9–1.8) whereas the Andersen and Lindsley (1988) calculations gave higher oxygen fugacity (fO2=1.1–2.5). Nevertheless, these results, irrespective the applied calculation methods, suggest relatively oxidized conditions (ΔNNO>1) what is comparable with many other andesitic to dacitic volcanic systems (e.g. Mount St. Helens, Mount Unzen, Santorini). Values of TiO2 activity was calculated and obtained a range between 0.76 and 0.98 what is consistent with the common presence of titanite.

 

This study was financed by NKFIH K135179 project.

 

Andersen, D.J. & Lindsley, D.H. (1985). EOS Transactions of the American Geophysical Union, 66, 416.

Andersen, D.J. & Lindsley, D.H. (1988). Amer Miner 73:714–726.

Ghiorso, M.S. & Evans, B.W. (2008). Amer J Sci 308:957–1039.

How to cite: Szemerédi, M., Mészáros, K., Lukács, R., Kovács, Z., and Harangi, S.: Constraints on the pre-eruption thermal and fO2 conditions in the magma reservoir of Ciomadul (SE Carpathians, Romania) based on Fe-Ti oxide geochemistry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14613, https://doi.org/10.5194/egusphere-egu21-14613, 2021.

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