Electrical Resistivity Structure of the Altiplano-Puna Magma Body and Volcan Uturuncu from Magnetotelluric Data

Matthew J. Comeau*

*Corresponding author for this work

Research output: ThesisDissertation (external)

Abstract

An intense episode of silicic volcanism in the Southern Altiplano over the past ten million years
has created a major volcanic province in the Central Andes known as the Altiplano-Puna
Volcanic Complex (APVC). Geophysical evidence indicates that magma is still present in a large
mid-crustal reservoir known as the Altiplano-Puna Magma Body (APMB). An analysis of the
geodetic data shows that the magma in the APMB is moving, causing observed surface
deformation. Broadband magnetotelluric (MT) data collected as part of this thesis were used to
generate two-dimensional and three-dimensional electrical resistivity models of the crust below
the APVC with the goal of imaging the melt distribution within and above the APMB. The twodimensional resistivity model gives new constraints on the east-west extent of the APMB,
whereas the three-dimensional resistivity model focuses on a spatially broad (~150 km) and
temporally continuous (decades) zone of deformation around Volcan Uturuncu in southern
Bolivia. Low electrical resistivities (< 3 m) at a depth of ~14 km below sea level are
interpreted as being due to the andesitic melts of the APMB and require a minimum melt fraction
of 15%. The upper surface of the APMB shallows beneath Volcan Uturuncu, where the inflation
is the fastest, and the geometry is consistent with geodynamic models that propose upward
movement of melt, in agreement with viscosity calculations derived from the MT data. The
shallower resistivity structure is characterized by several discrete electrically conductive bodies,
oriented approximately east-west and located close to sea level. These are interpreted as a
combination of dacitic partial melt and fluids, and are related to melt movement through the crust
and may be a pre-eruptive magma storage location. A quantitative comparison of the resistivity
models with seismic velocity models shows that a deep magma body with a silica-rich upper
layer can explain both datasets.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Alberta
Supervisors/Advisors
  • Unsworth , Martyn , Supervisor, External person
Place of PublicationEdmonton, Alberta, Canada
Publisher
DOIs
Publication statusPublished - 21 Sept 2015
Externally publishedYes

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