Thermal budgets of magma storage constrained by diffusion chronometry: the Cerro Galán ignimbrite

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Authors

Jordan Lubbers , Shan de Silva, Adam J Kent

Abstract

The long-term thermochemical conditions at which large bodies of silicic magma are stored in the crust is integral to our understanding of the timing, frequency, and intensity of volcanic eruptions, and provides important context for volcano monitoring data. Despite this realization, however, individual magmatic systems also may have unique time-temperature paths, or thermal histories, that are the result of many complex and, sometimes, simultaneous/competing processes, ultimately leading to an incomplete understanding of their long-term thermal evolution. Of recent interest to the volcanology community is the length of time large volumes of eruptible and geophysically detectable magma exist within the crust prior to their eruption. Here we use a combination of diffusion chronometry, trace element, and thermodynamic modeling to quantify the long-term thermal budget of the 2.08 Ma, 630km3 Cerro Galán Ignimbrite (CGI) in NW Argentina, one of the largest explosive volcanic eruptions in the recent geologic record. We find that diffusion of both Mg and Sr in plagioclase indicate that erupted magmatic material only spent decades to centuries at or above temperatures (~750°C) required to produce and store significant volumes of eruptible magma. Calculated plagioclase equilibrium liquid compositions reveal an array that is controlled overall by fractionation of plagioclase + biotite + sanidine, although high-resolution trace element transects record a diversity of long-term storage conditions with some plagioclase recording periods of co-crystallization with biotite and sanidine, while others do not. Despite these chemical differences in long-term storage, we find diffusion models record a unimodal distribution which, when combined with prior work revealing zircon residence times of ~105 years, and calculated zircon saturation temperatures of 807 ± 8°C, provide compelling evidence that the CGI magmatic system spent most of its upper crustal residence in a largely uneruptible state and was ultimately remobilized shortly before eruption.

DOI

https://doi.org/10.31223/X5B329

Subjects

Physical Sciences and Mathematics

Keywords

diffusion chronometry, Thermal history, caldera forming eruption, silicic magmatism, plagioclase

Dates

Published: 2021-12-02 07:20

License

CC BY Attribution 4.0 International

Additional Metadata

Data Availability (Reason not available):
All data underlying this article will be available in the article and in its online supplementary material. For now, until that is available please contact the corresponding author for supplementary data. Diffusion modeling code can be accessed in the following GitHub repository: https://github.com/jlubbersgeo/diffusion_chronometry.

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