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

点击翻译按钮获取中文摘要

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.