NSFGEO-NERC: Linking geophysics and volcanic gas measurements to constrain the transcrustal magmatic system at the Altiplano-Puna deformation anomaly

Lead Research Organisation: University of Bristol
Department Name: Earth Sciences


The path that magma takes through the crust is not well understood -- where is magma stored and under what conditions will it erupt? While this question is of fundamental scientific interest, it is also directly related to understanding the hazard posed by volcanic systems that are showing signs of activity and unrest. This proposal seeks to understand the cause of unrest and the architecture of the magma storage system within the central Andes, home to the world's largest geophysically imaged zone of silicic partial melt, the Altiplano-Puna Magma (or Mush) Body (APMB).
The new paradigm of a transcrustal magmatic system (TCMS) where magma is stored and undergoes chemical changes occurs at several locations throughout the entire crust. This conceptual revolution is being driven by petrological, geochronological, and geochemical studies of magma storage conditions that show (1) many large eruptions tap multiple melt sources, (2) large melt bodies are probably transient features, (3) crystals carried by the transporting melt have been stored at a range of pressures and temperatures. A key location to assess and refine models of currently active TCMS is at the APMB, where a large ground deformation pattern 150 km in diameter lasting several decades has been observed centered on Uturuncu volcano, Bolivia. By collecting and analyzing new interdisciplinary field measurements (gravity, ground deformation, seismic, gas flux and composition) and developing 3D numerical models, this proposal will answer several outstanding questions about the nature of TCMS at the APMB: 1. What is the cause of deformation in the midcrust at the APMB: a magmatic diapir, cyclic up and down movements from magma mush reorganization involving magma and/or volatiles, or something else? 2. What is the nature of a shallow-seated conductivity anomaly -- to what extent is it partial melt, a hydrothermal brine reservoir, or a mature ore body? 3. What is the flux of volatiles through the TCMS? 4. How important is crustal anisotropy in the interpretation of the subsurface magma plumbing architecture?
We propose a multi-parametric study to test specific aspects of the TCMS in the central Andes that could be broadly applicable to other TCMS currently active in the world and in the geologic record. Using a closely coordinated international geophysical and geochemical approach with funding from both the US NSF and UK NERC, we will test and refine the possible cause of the ground deformation, better constrain the shallow structure, determine whether deformation is still occurring, and make the first measurements of the volatile flux through the system.

Planned Impact

The proposed basic research will provide a better understanding of the nature of TCMS and is a broader impact because it provides insight into the natural processes that lead to volcanic unrest and potentially eruption that can then be applied elsewhere. The proposal will increase international cooperation between scientists in the US, UK and Bolivia and improve infrastructure for volcano monitoring in Bolivia at the Observatorio San Calixto (OSC), a private, non-profit organization that is responsible for seismic monitoring throughout the country. Although Bolivia has 12 potentially active volcanoes, there are no seismic stations near the volcanoes in southwest Bolivia or other geophysical or geochemical monitoring of these volcanoes. Thus, the 2-year seismic deployment will add to the limited understand of the background earthquake activity at the volcanoes that is necessary to better assess the hazard of future volcanic unrest -- what is normal activity and what should cause concern? OSC staff will participate in the work and have requested training in the field methods that we use (seismic, GNSS, gravity, and gas). We share all data immediately upon collection with OSC and we collaborate together in the interpretation. The project also involves training of at least one female graduate student.
Description We conducted a geophysical survey of the target area and were able to shed light on the density distribution beneath Uturuncu volcano down to a depth of 5km. The data highlight a hitherto unknown positive density anomaly within the volcanic edifice. Further analysis are currently underway to identify the nature of this anomaly.
Exploitation Route Modelling of the geophysical data will shed light on the subsurface architecture. The data can then be used by others to inform their geophysical subsurface models and data interpretation
Sectors Environment

Description Collaboration with NSF funded part of project 
Organisation Cornell University
Country United States 
Sector Academic/University 
PI Contribution Joint fieldwork and data collection
Collaborator Contribution Joint fieldwork and data collection
Impact Visiting professorship to Bristol for US partner Prof. M. Pritchard
Start Year 2018