EGU2020-19199
https://doi.org/10.5194/egusphere-egu2020-19199
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The role of basaltic magma in the petrogenesis of the Late Pleistocene Ciomadul dacite, Romania

Szabolcs Harangi1,2, Maurizio Petrelli3, Balázs Kiss1, Olivier Bachmann4, Ioan Seghedi5, Theodoros Ntaflos6, Éva Jankovics1, and Réka Lukács1
Szabolcs Harangi et al.
  • 1MTA TKI, Budapest, Hungary (szabolcs.harangi@geology.elte.hu)
  • 2Department of Petrology and Geochemsitry, Eötvös Loránd University, Budapest, Hungary
  • 3University of Perugia, Perugia, Italy (maurizio.petrelli@unipg.it)
  • 4ETH Zürich, Zürich, Switzerland (olivier.bachmann@erdw.ethz.ch)
  • 5Institute of Geodynamics, Romanian Academy, Bucharest, Romania (seghedi@geodin.ro)
  • 6Department of Lithospheric Research, University of Vienna, Vienna, Austria (theodoros.ntaflos@univie.ac.at)

The Ciomadul in eastern-central Europe is a high-K dacitic volcanic complex characterized by long quiescence (several 10’s of kyr) periods between eruptions and a long-standing (over several 100’s of kyr) magmatic plumbing system. Following intermittent lava dome extrusions from 1 Ma to 360 ka, a more intense eruption stage occurred between 160 ka and 30 ka with initial lava dome building period followed by dominantly explosive eruptions. The volcano has been again in a long quiescence stage since 30 ka, although results of geophysical studies suggest presence of a subvolcanic magma body with significant melt fraction. In order to constrain better the rejuvenation mechanism of such long-dormant volcanic complex, a more thorough understanding of the nature and dynamics of the magmatic plumbing system and the reason of eruption triggers is required. In spite of the homogeneous dacitic bulk rock composition and similar mineral assemblage, each eruption product shows subtle differences in mineral-scale features. Here, we present examples showing how basaltic magma played a role in the genesis of dacite as well as triggered eruption in a timescale of days to weeks.
The Ciomadul dacites are crystal rich and contain plagioclase, amphibole and biotite as main phenocrysts in addition to accessory phases of apatite, titanite and zircon. Several dacitic lava dome rocks formed between 90 and 160 ka in Ciomadul contain also high-Mg minerals such as olivine, clinopyroxene and orthopyroxene. Cr-spinel inclusions occur in olivine, orthopyroxene and also in high-Al amphiboles. Textures and the high Mg-numbers (0.85-0.91) of these mineral phases suggest that they can be considered as antecrysts with magmatic origin having crystallised from primitive mafic magmas, which were involved in the evolution of the subvolcanic magma storage system. Zoning pattern and trace element content of plagioclases and amphiboles clearly show interaction between dacitic and basaltic magmas. In addition, these high-Mg minerals allow us to have an insight into the origin of the primary magmas as well as the dynamics of the mafic magma body stalled at the crust-mantle boundary.
The compositions of the Cr-spinel inclusions significantly differ from those of the spinels in the 600-1200 ka alkaline basalts of the nearby Perşani Volcanic Field and their high Cr-numbers indicate a depleted mantle source for the parental magma. Such Cr-rich spinels are common in high-K magmas originated in metasomatized lithospheric mantle with depleted, harzburgitic lithology. Compositional zoning of clinopyroxenes indicates several recharge events by high-Mg and high-Cr basaltic magmas. Mafic magma batches repeatedly ascended and emplaced below the upper crustal felsic crystal mush and formed a dynamic interface between these two magmas. The mafic components remained in plastic state allowing thorough mixing of the mafic and felsic mineral cargos during turbulent convective magma stirring, whereas farther from this interface, remelting of the crystal mush occurred due to reheating and volatile transfer into the interstitial melt. The series of mafic magma injections increased the eruptible magma volume and occasionally led to eruptions.
This research was financed by the Hungarian National Research, Development and Innovation Fund (NKFIH) within K116528 project.

How to cite: Harangi, S., Petrelli, M., Kiss, B., Bachmann, O., Seghedi, I., Ntaflos, T., Jankovics, É., and Lukács, R.: The role of basaltic magma in the petrogenesis of the Late Pleistocene Ciomadul dacite, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19199, https://doi.org/10.5194/egusphere-egu2020-19199, 2020

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Presentation version 2 – uploaded on 04 May 2020
figure is updated in slide 23
  • CC1: Comment on EGU2020-19199, Agustin Cardona, 05 May 2020

    Very nice work. Some questions: 1) It was not clear for me what was the percentages of the crystal cargo available when the mafic magma rechage came to the magmas. 2) Ypu mention on the abstract that the magmas are probabbly of high-K character, however it doesn´t elaborate it.  Is the high-k signature related to enriched mantle.

    • AC1: Reply to CC1, Szabolcs Harangi, 05 May 2020

      Very nice work.

      Thank you!

      Some questions: 1) It was not clear for me what was the percentages of the crystal cargo available when the mafic magma rechage came to the magmas.

      We can estimate it based on the felsic crystal clots in the dacite which suggest 80-90%, whereas we estimated it also based on magnetotellurics, conductivity experiments and thermal modeling what indicate locally even up to 40% melt (see Laumonier et al. paper in EPSL 2019)

      2) Ypu mention on the abstract that the magmas are probabbly of high-K character, however it doesn´t elaborate it.  Is the high-k signature related to enriched mantle.

      Yes, we think that it is a source character, i.e. the primary melts could have generated in a lithospheric mantle enriched in K, Ba, Sr...

  • CC2: Comment on EGU2020-19199, Tobias Keller, 05 May 2020

    Hi Szabolcs! Further to your exchange with Luca in the chat session, I'm working on a data science tool that estimates the number, composition and mixing abundances of magma endmembers in geochemical datasets. If you're interested we could run your data through the algorithm to get an estimate?

    • AC2: Reply to CC2, Szabolcs Harangi, 05 May 2020

      Hi Tobias,

      many thanks for your comment, I will certainly contact you discussing this opportunity!

      Cheers, Szabi

Presentation version 1 – uploaded on 04 May 2020 , no comments