Magnetotelluric investigations at Andean volcanoes: Partial melt or saline magmatic fluids?

Alex P Jenkins*, Alison C Rust, Jon D Blundy, Juliet Biggs

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

1 Citation (Scopus)
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Abstract

Knowledge of the architecture of active magmatic systems is important for both volcanic hazard assessment and evaluating potential geothermal energy production and metals recovery from magmatic fluids. Increasingly, magmatic systems are imaged using the magnetotelluric method to detect electrically conductive partial melt and/or saline magmatic fluid reservoirs. We review recent magnetotelluric studies at eight Andean volcanoes, revealing electrical conductivity anomalies with variable magnitudes and locations. Six of the studied volcanoes exhibit three main electrical conductivity anomalies, located at shallow (<3 km), intermediate (=5 km), and deep (>10 km) depths. The shallow anomalies are often thin and laterally extensive, consistent with clay cap alteration layers, while the deep anomalies are generally interpreted as partial melt reservoirs. The intermediate depth anomalies, although also often attributed to partial melt, have less clear origins. By analysing laboratory-derived electrical conductivity relationships, we show that the intermediate depth anomalies are generally most consistent with saline magmatic fluids stored in porous rock. However, other geophysical and petrological data suggest that localised partial melt also exists at intermediate depths. Therefore, the intermediate depth anomalies likely represent mixed melt and saline magmatic fluid systems, such as those responsible for forming magmatic-hydrothermal alteration zones and copper porphyry deposits. At individual volcanoes, refining the generalised three layer model proposed here by using additional geophysical or petrological data is key to constraining the resources and/or hazard potential of the magmatic system.
Original languageEnglish
Article number107852
JournalJournal of Volcanology and Geothermal Research
Volume440
Early online date4 Jul 2023
DOIs
Publication statusPublished - 1 Aug 2023

Bibliographical note

Funding Information:
This work was supported by the Natural Environment Research Council [NE/L002434/1]. A. Jenkins, A. Rust, and J. Blundy were partially supported by BHP. A. Jenkins and J. Biggs were supported by the NERC Centre for the Observation and Modeling of Earthquakes, Volcanoes and Tectonics (COMET: http://comet.nerc.ac.uk), a partnership between UK Universities and the British Geological Survey. J. Biggs and A. Rust received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (MAST: grant agreement No. 101003173). J. Blundy acknowledges a Royal Society Research Professorship (RP\R1\201048). A. Jenkins and A. Rust attended the IMPROVE/NordVulk summer school on geothermal and magmatic systems held in Iceland during June 2022, which helped to develop the ideas presented here. Helpful and constructive reviews by Martyn Unsworth and an anonymous reviewer improved the original manuscript.

Funding Information:
This work was supported by the Natural Environment Research Council [NE/L002434/1]. A. Jenkins, A. Rust, and J. Blundy were partially supported by BHP. A. Jenkins and J. Biggs were supported by the NERC Centre for the Observation and Modeling of Earthquakes, Volcanoes and Tectonics (COMET: http://comet.nerc.ac.uk ), a partnership between UK Universities and the British Geological Survey . J. Biggs and A. Rust received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (MAST: grant agreement No. 101003173). J. Blundy acknowledges a Royal Society Research Professorship (RP\R1\201048). A. Jenkins and A. Rust attended the IMPROVE/NordVulk summer school on geothermal and magmatic systems held in Iceland during June 2022, which helped to develop the ideas presented here. Helpful and constructive reviews by Martyn Unsworth and an anonymous reviewer improved the original manuscript.

Publisher Copyright:
© 2023 The Author(s)

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