Evaluating the Role of Titanomagnetite in Bubble Nucleation: Novel Applications of Low Temperature Magnetic Analysis and Textural Characterization of Rhyolite Pumice and Obsidian From Glass Mountain, California

Authors

Kelly N. McCartney, University of Hawaiʻi at Mānoa
Julia E. Hammer, University of Hawaiʻi at Mānoa
Thomas Shea, University of Hawaiʻi at Mānoa
Stefanie Brachfeld, Montclair State UniversityFollow
Thomas Giachetti, University of Oregon

Document Type

Article

Publication Date

4-1-2024

Journal / Book Title

Geochemistry Geophysics Geosystems

Abstract

Nucleation of H2O vapor bubbles in magma requires surpassing a chemical supersaturation threshold via decompression. The threshold is minimized in the presence of a nucleation substrate (heterogeneous nucleation, < 50 MPa), and maximized when no nucleation substrate is present (homogeneous nucleation, >100 MPa). The existence of explosively erupted aphyric rhyolite magma staged from shallow (< 100 MPa) depths represents an apparent paradox that hints at the presence of a cryptic nucleation substrate. In a pair of studies focusing on Glass Mountain eruptive units from Medicine Lake, California, we characterize titanomagnetite nanolites and ultrananolites in pumice, obsidian, and vesicular obsidian (Brachfeld et al., 2024, https://doi.org/10.1029/2023GC011336), calculate titanomagnetite crystal number densities, and compare titanomagnetite abundance with the physical properties of pumice to evaluate hypotheses on the timing of titanomagnetite crystallization. Titanomagnetite crystals with grain sizes of approximately 3–33 nm are identified in pumice samples from the thermal unblocking of low-temperature thermoremanent magnetization. The titanomagnetite number densities for pumice are 10¹⁸ to 10²⁰ m⁻³, comparable to number densities in pumice and obsidian obtained from room temperature methods (Brachfeld et al., 2024, https://doi.org/10.1029/2023GC011336). This range exceeds reported bubble number densities (BND) within the pumice from the same eruptive units (average BND ∼4 × 10¹⁴ m⁻³). The similar abundances of nm-scale titanomagnetite crystals in the effusive and explosive products of the same eruption, together with the lack of correlation between pumice permeability and titanomagnetite content, are consistent with titanomagnetite formation having preceded the bubble formation. Results suggest sub-micron titanomagnetite crystals are responsible for heterogeneous bubble nucleation in this nominally aphyric rhyolite magma.

Comments

This is an open access article under the terms of the Creative Commons Attribution 4.0 License (https://creativecommons.org/licenses/by/4.0/).

DOI

10.1029/2023GC011338

Journal ISSN / Book ISBN

85191038322 (Scopus)

MSU Digital Commons Citation

McCartney, Kelly N.; Hammer, Julia E.; Shea, Thomas; Brachfeld, Stefanie; and Giachetti, Thomas, "Evaluating the Role of Titanomagnetite in Bubble Nucleation: Novel Applications of Low Temperature Magnetic Analysis and Textural Characterization of Rhyolite Pumice and Obsidian From Glass Mountain, California" (2024). Department of Earth and Environmental Studies Faculty Scholarship and Creative Works. 715.
https://digitalcommons.montclair.edu/earth-environ-studies-facpubs/715

Published Citation

McCartney, K. N., Hammer, J. E., Shea, T., Brachfeld, S., & Giachetti, T. (2024). Evaluating the role of titanomagnetite in bubble nucleation: Novel applications of low temperature magnetic analysis and textural characterization of rhyolite pumice and obsidian from Glass Mountain, California. Geochemistry, Geophysics, Geosystems, 25, e2023GC011338. https://doi.org/10.1029/2023GC011338