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    Reactivation of fault systems by compartmentalized hydrothermal fluids in the Southern Andes revealed by magnetotelluric and seismic data

    Pearce, R. K. and Sánchez de la Muela, A. and Moorkamp, M. and Hammond, James O.S. and Mitchell, T. M. and Cembrano, J. and Araya Vargas, J. and Meredith, P. G. and Iturrieta, P. and Pérez Estay, N. and Marshall, N. R. and Smith, J. and Yañez, G. and Griffith, W. Ashley and Marquardt‐Román, C. and Stanton‐Yonge, A. and Núñez, R. (2020) Reactivation of fault systems by compartmentalized hydrothermal fluids in the Southern Andes revealed by magnetotelluric and seismic data. Tectonics , ISSN 0278-7407. (In Press)

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    Abstract

    In active volcanic arcs such as the Andean volcanic mountain belt, magmatically‐sourced fluids are channelled through the brittle crust by faults and fracture networks. In the Andes, volcanoes, geothermal springs and major mineral deposits have a spatial and genetic relationship with NNE‐trending, margin‐parallel faults and margin‐oblique, NW‐trending Andean Transverse Faults (ATF). The Tinguiririca and Planchón‐Peteroa volcanoes in the Andean Southern Volcanic Zone (SVZ) demonstrate this relationship, as their spatially associated thermal springs show strike alignment to the NNE‐oriented El Fierro Thrust Fault System. We constrain the fault system architecture and its interaction with volcanically sourced hydrothermal fluids using a combined magnetotelluric (MT) and seismic survey that was deployed for 20 months. High conductivity zones are located along the axis of the active volcanic chain, delineating fluids and/or melt. A distinct WNW‐trending cluster of seismicity correlates with resistivity contrasts, considered to be a reactivated ATF. Seismicity occurs below 4 km, suggesting activity is limited to basement rocks, and the cessation of seismicity at 9 km delineates the local brittle‐ductile transition. As seismicity is not seen west of the El Fierro fault, we hypothesize that this structure plays a key role in compartmentalizing magmatically‐derived hydrothermal fluids to the east, where the fault zone acts as a barrier to cross‐fault fluid migration and channels fault‐parallel fluid flow to the surface from depth. Increases in fluid pressure above hydrostatic may facilitate reactivation. This site‐specific case study provides the first three‐dimensional seismic and magnetotelluric observations of the mechanics behind the reactivation of an ATF.

    Metadata

    Item Type: Article
    Additional Information: This is the peer reviewed version of the article, which has been published in final form at the link above. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
    Keyword(s) / Subject(s): Faulting and Hydrothermal Fluids, Magnetotelluric Inverse Modelling, Seismic Hypocenter Locations, Andean Southern Volcanic Zone, Volcanism and Faulting
    School: School of Science > Earth and Planetary Sciences > UCL/Birkbeck Centre for Planetary Sciences
    School of Science > Earth and Planetary Sciences
    Depositing User: James Hammond
    Date Deposited: 23 Nov 2020 11:01
    Last Modified: 10 Jun 2021 06:20
    URI: https://eprints.bbk.ac.uk/id/eprint/41528

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