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

• Author / Creator

  Comeau, Matthew J

• 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 two-dimensional 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 ohm-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.

• Subjects / Keywords

  • Altiplano
  • Geophysics
  • Resistivity
  • Inversion
  • Andes
  • Magma
  • Volcano
  • Magnetotellurics
  • Supervolcano

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3C24QW2S

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.