EGU2020-9187
https://doi.org/10.5194/egusphere-egu2020-9187
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Imaging magma storage in the Main Ethiopian Rift with 3-D Magnetotellurics

Juliane Huebert1,2, Kathy Whaler1, Shimeles Fisseha3, Fiona Iddon4, and Colin Hogg5
Juliane Huebert et al.
  • 1School of Geosciences, University of Edinburgh, UK (juliane.huebert@ed.ac.uk)
  • 2British Geological Survey, Edinburgh, UK
  • 3Institute of Geophysics, Space Science and Astronomy, Addis Ababa University, Ethiopia
  • 4Department of Earth Sciences, University of Cambridge, UK
  • 5Dublin Institute for Advanced Studies, Dublin, Ireland

The Main Ethiopian Rift (MER) as part of the large East African continental break-up zone is characterized by lateral extension and active volcanism. Rifting in the MER is magma assisted, with surface expressions of magmatism concentrated at en echelon Quaternary magmatic segments and off-axis linear features, but questions still remain about their respective roles in rifting.

The storage and pathways of magma ascent are of great interest for the assessment of both geohazard and geothermal energy potential. Imaging magma storage throughout the crust and in the upper mantle can be achieved by geophysical deep sounding techniques such as magnetotellurics (MT). Through MT measurements it is possible to access the electrical conductivity of the subsurface, a parameter that is greatly sensitive to the melt and water content. We present new MT data from the Central MER and a three-dimensional model of conductivity of the crust, imaging across-rift magma storage not only under the well-developed central-axis silicic volcanic complex Aluto, but also under several off-axis basaltic monogenetic volcanic fields. The conductivity model supports the idea of bi-modal magma storage in the CMER and helps constrain the melt and water content in the crust through the use of petrological melt-mixing models. Integrating our findings with the results from seismic tomography and receiver functions as well as Bouguer gravity data and petrological observations allows a comprehensive picture of magma storage and pathways in the MER.

How to cite: Huebert, J., Whaler, K., Fisseha, S., Iddon, F., and Hogg, C.: Imaging magma storage in the Main Ethiopian Rift with 3-D Magnetotellurics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9187, https://doi.org/10.5194/egusphere-egu2020-9187, 2020

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  • CC1: Comment on EGU2020-9187, David Martínez van Dorth, 06 May 2020

    Hello!

    This survey must have been very exciting because of the place and also measuring over a rift zone. 

    I have some questions. At depth 18403.5 m you show a large conductive body. Is this body related to the magma from the rift? Do you know if this conductive body is continuous along the rift? And what are these higher resistive bodies at 3960.5 m depth?

    I don't know if there are more MT measurements along the entire rift in order to characterize it but your work is very interesting and brings light to see what we can find in this volcanic sites at depth. My congratulations! 

    Best wishes,

    David MvD.

    • AC1: Reply to CC1, Juliane Huebert, 06 May 2020

      Dear David,

      thank you for your interest and enthusiasm! Field work in the rift was definitely a challenging experience in a unique environment. Our work was following on from several previous MT (and other) studies in Ethiopia, some of which are cited in my last paper https://doi.org/10.1029/2017JB015160

      Regarding your questions about the model, we interpret the higher resistive zones as possibly cooled igneous intrusions. The central volcano Aluto had its last caldera phase eruption ~200ky ago, so anthing that wasn't erupted then cooled in the crust, causing high density and high resistivity anomalies. The deeper conductor in the lower crust is something we would associate and expect to be higher percentages of melt, a reservoir for recent volcanism. We found that in comparison with MT profiles from further north in the MER and Afar the average crustal resistivity in our area is higher, which maybe be related to the evolution of the rift and how much melt is stored here. Our model is the first 3-D rift-wide model, MT data further north is mainly along profiles. Then there are higher-resolution surveys around hydrothermal reservoirs, e.g. Samrock et al. 2015, 2019.

      Hope that is illuminating your questions. Let me know if there are any other related to our work.

       

      Cheers, Juliane

       

      • CC2: Reply to AC1, David Martínez van Dorth, 08 May 2020

        First of all, sorry for my late reply. 

        So, knowing that your part is a little bit more resistive in depth, we can say that the rift evolves in different parts, right? It might be obvious this evolution but well, this could be one way to demostrate the evolution of rifts in parts.

        It is also interesting to see the presence of multiple igneous intrusions at certain depths, it's just amazing. This will help me with my studies.

        Once again, incredible work! Thank you very much, Juliane!

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