Metal-Rich Brines and Where to Find Them: Using Seismic Attenuation to Image and Identify Fluids Beneath Uturuncu Volcano, Bolivia
Abstract
How, when and where fluids accumulate in the crust are pertinent for volcanic hazard assessment, geothermal energy generation and mineral exploration. Here, we use seismic attenuation tomography and S-wave anisotropy to map the migration and accumulation of fluids beneath Uturuncu volcano, Bolivia. Uturuncu is a particularly interesting setting for exploring methods for mapping subsurface fluids, since there are both regions of molten rock and a shallow hydrothermal system, emplaced in an otherwise presumably dry crust. High P-wave and S-wave attenuation elucidate the presence of fluids in the crust, with their ratio (QP/QS), constraining where the crust is partially fluid-saturated with gas-incompressible fluid mixtures or supercritical fluids (QP/QS < 1); and fully fluid-saturated with incompressible fluids (QP/QS > 1). Furthermore, seismic anisotropy indicates the mechanism by which fluids accumulate, predominantly along faults in this case. We combine these seismic observations with subsurface pressure-temperature profiles, crustal resistivity tomography from magnetotellurics, and numerical models of fluid compressibility. Combined with our seismic observations, these data allow us to identify the most likely fluid compositions in different regions of the crust. We identify shallow regions of both dry and H2O/brine-saturated crust, with and without gases percolating through them. We also identify a deeper supercritical H2O/brine column directly beneath Uturuncu that drives fluid flow into the shallow subsurface. The conductivity of these regions suggests that these brines could potentially be rich in metals. Finally, we also tentatively image a pocket of isolated, partially-molten dacite. Our observations provide a greater understanding of Uturuncu's transcrustal hydrothermal system, and act as an example of how such methods could be applied to map crustal fluid pathways and hydrothermal/geothermal systems elsewhere.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.V33A..01H