Noble Gas Analysis of Volcanic Glass Particles: A Better Understanding of Volcano Degassing and Implications for Ar/Ar Dating of Eruptions

Cogliati, Simone (2019). Noble Gas Analysis of Volcanic Glass Particles: A Better Understanding of Volcano Degassing and Implications for Ar/Ar Dating of Eruptions. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0001098f

Abstract

Noble Gases (NG) have been investigated extensively in a variety of volcanic materials, however, few efforts have been made to study their incorporation, partition and release to and from subaerial volcanic glass. In this study, 4He, 22Ne, 36Ar, 40Ar, trapped in different subaerial volcanic glass types, are used to characterize magmatic reservoirs, to study volcanic processes, to investigate the degassing and evolution of volcanic systems and to understand the implications for the Ar/Ar system.

Glass shards from silicic tuffs interbedding basaltic lavas of the Columbia River Basalt Group (CRBG - Washington, U.S.) yielded accurate, precise Ar/Ar ages (12.00±0.24 Ma, 11.37±0.15 Ma, 10.67±0.21 Ma, 10.70±0.18 Ma, 10.77±0.18 Ma). These were used to indirectly constrain better the timing of eruption of two Formations of the CRBG and to aid the correlation of the tuffs with their eruptive centre (Bruneau-Jarbidge) in the Central Snake River Plain.

NG in Pele’s hairs and tears were used to monitor the degassing of Masaya volcano (Nicaragua) between 2015 - 2016. The variations of the NG in the samples were attributed to the upward migration of a gas-rich magma from depth in 2015. The NG abundances in single particles are controlled by sample vesicularity and by solubility and diffusion fractionation of the gas prior eruption.

Pre-, syn- and post-eruptive processes interplay and superimpose upon each other, complicating the interpretation of Ar/Ar ages and NG abundances in pumice glass particles. The NG variations in glass particles from different portions of a pumice fall and an ignimbrite from the Eras Formation (Tenerife) are attributed to a “stratified” magma chamber with respect to NG, and, to diffusion fractionation processes that acted during pumice cooling. Glass particles failed to provide Ar/Ar ages and no relationships were observed between Ar degassing and Ar/Ar ages produced from different portions of the eruptive sequence.

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