We document the presence, composition, and number density (TND) of titanomagnetite nanolites and ultra‐nanolites in aphyric rhyolitic pumice, obsidian, and vesicular obsidian from the 1060 CE Glass Mountain volcanic eruption of Medicine Lake Volcano, California, using magnetic methods. Curie temperatures indicate compositions of Fe2.40Ti0.60O4 to Fe3O4. Rock‐magnetic parameters sensitive to domain state, which is dependent on grain volume, indicate a range of particle sizes spanning superparamagnetic (<50–80 nm) to multidomain (>10 μm) particles. Cylindrical cores drilled from the centers of individual pumice clasts display anisotropy of magnetic susceptibility with prolate fabrics, with the highest degree of anisotropy coinciding with the highest vesicularity. Fabrics within a pumice clast require particle alignment within a fluid, and are interpreted to result from the upward transport of magma driven by vesiculation, ensuing bubble growth, and shearing in the conduit. Titanomagnetite number density (TND) is calculated from titanomagnetite volume fraction, which is determined from ferromagnetic susceptibility. TND estimates for monospecific assemblages of 1,000 nm–10 nm cubes predict 10^12 to 10^20 m^−3 of solid material, respectively. TND estimates derived using a power law distribution of grain sizes predict 10^18 to 10^19 m^−3. These ranges agree well with TND determinations of 10^18 to 10^20 m^−3 made by McCartney et al. (2024), and are several orders of magnitude larger than the number density of bubbles in these materials. These observations are consistent with the hypothesis that titanomagnetite crystals already existed in extremely high number‐abundance at the time of magma ascent and bubble nucleation.
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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 (Dataset)
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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- Award ID(s):
- 1839313
- NSF-PAR ID:
- 10513798
- Publisher / Repository:
- Earthref Magnetics Information Consortium
- Date Published:
- Subject(s) / Keyword(s):
- Rhyolite Obsidian Glass Mountain Titanomagnetite Nanolites Magnetic Susceptibility Bubble Nucleation anhysteretic remananent magnetization hysteresis parameters
- Format(s):
- Medium: X
- Location:
- earthref.org/MagIC/20020
- Institution:
- Montclair State University
- Sponsoring Org:
- National Science Foundation
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