This dataset archived with the Magnetics Information Consortium contains rock-magnetic data for rhyolitic pumice and obsidian from Glass Mountain, Medicine Lake, California, USA. Data were generated at Montclair State University and include magnetic susceptibility measured at 976Hz and 3904Hz, magnetic susceptibility vs. temperature, anhysteretic remanent magnetization (ARM), and magnetic hysteresis measurements. This dataset accompanies the publication Brachfeld, S., McCartney, K., Hammer, J.E., Shea, T., Giachetti, T., Evaluating the role of titanomagnetite in bubble nucleation: Rock magnetic detection and characterization of nanolites and ultra-nanolites in rhyolite pumice and obsidian from Glass Mountain, California, Geochemistry Geophysics Geosystems, https://doi.org/10.1029/2023GC011336.
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This content will become publicly available on April 1, 2025
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
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 10^18 to 10^20 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'>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 × 10^14 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.
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- NSF-PAR ID:
- 10502181
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 25
- Issue:
- 4
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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