garnet within qbt rick warren and fraser goff retired, los alamos national laboratory
TRANSCRIPT
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Garnet within Qbt
Rick Warren and Fraser Goff
Retired, Los Alamos National Laboratory
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Thin sections for SWNVF
![Page 3: Garnet within Qbt Rick Warren and Fraser Goff Retired, Los Alamos National Laboratory](https://reader036.vdocuments.site/reader036/viewer/2022062322/5697bfc31a28abf838ca59d1/html5/thumbnails/3.jpg)
Garnet habits in volcanics
Grain shown is largest found, .091 mm (91,000 square microns)
SWNVF: GT in 60 of 313 thin sectionsJVF: GT in 10 of 76 thin sections
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Garnet areas in thin section
SWNVF only131 grains
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Stratigraphic units and lithologies
• All stratigraphic assemblages for SWNVF
• From base to top of Qbt for JVF
• Fractions of each lithology for SWNVF:– 62% are nonwelded tuff– 15% are welded tuff– 12% are alluvia– 7% are vitrophyric tuff– 3% are rhyolite lava
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Garnet in Qbt(10 of 67 thin sections)
Subunit (location)
Thin sections
TS with GT
ppmV GT-bearing Lithics
ppmV GT in MX
5 (Plateau) 12 2 61 1.3
4u (Vent) 2 2 21300 235
4u (Other Valles)
10 4 3120 0
l (Valles) 4 2 0 1.3
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Garnet in sandstone lithics
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Garnet necklaces in argillite lithics
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BSE image of argillite lithics
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Garnet compositions
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Origin of garnet in volcanics
• Necklaces require pneumatolytic origin
• Carbonates completely absent
• Argillites can provide Ca, Fe for andradite
• Andradite also forms in other host lithics
• Almandines likely detrital
• Prevalence in SWNVF suggests that pneumatolytic andradite/grossular may commonly form in rhyolite vents