EGU General Assembly 2020
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3D Geodynamic Models of the Present-Day Altiplano-Puna Magmatic System

Arne Spang, Tobias Baumann, and Boris Kaus
Arne Spang et al.
  • Institute of Geosciences, Johannes Gutenberg-University, Mainz, Germany

For the past decades, several numerical studies have successfully reproduced the concentric uplift pattern observed above the Altiplano-Puna Magma Body (APMB) in the central Andes. However, the temperature- and strain rate-dependent viscoelastoplastic rheology of rocks, the buoyancy of magma, the effects of modelling in 3D as well as the shape of the magma body have often been simplified or neglected.

Here, we use a joint interpretation of seismic imaging and gravity anomalies to constrain location, 3D shape and density of the magma body. With the help of the thermo-mechanical finite difference code LaMEM, we then model the surface deformation and test our results against observations made by Interferometric Synthetic-Aperture Radar (InSAR) missions. This way, we gain insights into the dynamics and rheology of the present-day magmatic system and can test how a change to the current conditions (e.g., magma influx) could impact it.

We find that only an APMB with a maximum thickness of 14 to 18 km and a corresponding density contrast to the surrounding host rock of 100 to 175 kg/m3 satisfies both tomography and Bouguer data. Based on that and the chemistry of eruption products, we estimate the melt content of the APMB to be on the order of 20 - 25%. We also find that the observed uplift can be reproduced by magma-induced buoyancy forces without the need for an additional pressure source or magma injection within the mush, and that the geometry of the top of the magma body exerts a major control on the deformation pattern at the surface.

How to cite: Spang, A., Baumann, T., and Kaus, B.: 3D Geodynamic Models of the Present-Day Altiplano-Puna Magmatic System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5388,, 2020

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Presentation version 2 – uploaded on 03 May 2020
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  • CC1: Questions and answers from the live chat during EGU2020, Michael Heap, 11 May 2020

    Q: Is the observed uplift pattern and rate always the same?

    A: It has been almost constant for 20 years of observations. It slightly decreasing in the lat few years

    Q: As I understood, you need a central rise to explain the deformation pattern. What would be the cause of this central rise? I mean why the rise should be focused in a central area?

    A: I have two ideas for that. 1.) It may be old magma pathways 2.) It might be the spot where new melts intrude, so it would be hotter and weaker than everywhere else

    Q: Main differences to previous studies?

    A: Main difference is the full visco-elasto-plastic rheology and the fact that we do not use a inflating pressure source but instead everything is driven by density (Stokes Code)

    Q: Hello, what rheology did you assume for bedrock and magma appart from buoyancy contrasts ?

    A: Viscoelastoplastic, using nonlinear creep laws

    Q: Thanks. Interesting modeling approach. Can you distinguish this model from a vertical flow, i.e. depressurization in a deeper source and pressure increase in a shallow source.

    A: Previous studies can reproduce the data with that kind of model. we never tested it

    Q: How did you parameterise the visco-elasto-plastic rheology?

    A: Lab. experiments show that rocks are viscoelastoplastic (to first order), so I am not sure what you mean with parameterisation

Presentation version 1 – uploaded on 03 May 2020 , no comments