The behavior of light lithophile and halogen elements in felsic magma: geochemistry of the post-caldera Valles Rhyolites, Jemez Mountains Volcanic Field, New Mexico

Stix, John; Layne, Graham D.; Spell, Terry L.

doi:10.1016/0377-0273(94)00098-2

Cited by 7 publications

(4 citation statements)

References 29 publications

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“…Using this evidence, they suggested that more primitive, high-Ti rhyolite magma was introduced at the base of the magma chamber before the LBT eruption and then mixed with the more differentiated rhyolite already there. Our data also support this model, in particular Be, which behaves similarly to higher mass incompatible trace elements [Ryan and Langrnuir, 1988;Stix et al, 1995a] and which is probably not sensitive to degassing. Thus the Be variability observed in 15-8 is evidence that crystals from the two magmas were mixed in the magma chamber before and/or during eruption.…”

Section: Dunbar and Herrig [1992a] Have Documented Two Populations Ofsupporting

confidence: 81%

Gas saturation and evolution of volatile and light lithophile elements in the Bandelier magma chamber between two caldera‐forming eruptions

Stix¹,

Layne²

1996

J. Geophys. Res.

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We have studied the distribution of light and volatile elements (Li, Be, B, H2O, F, Cl) in matrix glasses and melt inclusions in quartz and sanidine phenocrysts from tephras of the Cerro Toledo Rhyolite, which were erupted from the Bandelier magma chamber between two caldera‐forming eruptions at 1.608 Ma and 1.225 Ma. Since the small‐volume tephras of the Cerro Toledo Rhyolite record chemical evolution of the upper parts of the magma chamber during this 383‐kyr period, we can track volatile evolution in the magma during its differentiation, specifically, the development of a separate fluid phase from the magma, the partitioning of volatile and light elements between this fluid and the magma, and the timing of the second caldera eruption at 1.225 Ma. The melt inclusion data reveal that Li, Be, and B were progressively enriched with time at the top of the magma chamber, showing a similar three fold enrichment. By contrast, F, Cl, and F2O show more variable behavior. F was enriched 3.6 times in the magma and Cl increased 2.5 times, while water concentrations remained constant. Evidence for a separate fluid phase includes (1) comparatively small magmatic enrichment factors for Cl and H2O, elements which are known to partition into fluid, (2) decline of the Cl/Be and Cl/B ratios in melt inclusions with time, indicating preferential loss of Cl, and (3) maximum Cl contents of 2900–3000 ppm in melt inclusions, which are concentrations at or close to the saturation limit for Cl in a two‐phase gas‐saturated magma. The lack of temporal H2O enrichment in the magma suggests that it became gas saturated at an early stage. The Cl fluid‐magma partition coefficient was initially low, due to the presence of a low‐salinity single‐phase vapor. The fluid is calculated to have increased its salinity from 0.76 wt % equivalent NaCl to 3.1 wt % NaCl by crystallization and Cl enrichment in the magma. Consequently, the fluid was transformed to two immiscible phases. As a result, the Cl partition coefficient increased, and the Cl content in the magma was buffered at 2900–3000 ppm. Overpressures in the magma chamber have been modeled as a function of crystallization, total pressure and depth, H2O solubility in rhyolite, resurgence, crystallization contraction, and initial fluid mass. For the large amounts of crystallization (40–70%) required by the geochemical relations, unrealistically large overpressures (>75 MPa) are indicated, unless (1) the magma existed as a foam or (2) the chamber was able to degas passively, and thus buffer the buildup of pressure. To maintain realistic overpressures in the magma chamber (<50 MPa), an equilibrium was required between gas buildup by crystallization and volatile loss by passive degassing. The change from a one‐phase vapor to a two‐phase immiscible fluid before the Upper Bandelier Tuff eruption may have promoted partial or complete sealing of the magmatic‐hydrothermal system, permitting significant overpressures to develop. The result could have been a cataclysmic caldera‐forming eruption.

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Section: Dunbar and Herrig [1992a] Have Documented Two Populations Ofsupporting

confidence: 81%

Gas saturation and evolution of volatile and light lithophile elements in the Bandelier magma chamber between two caldera‐forming eruptions

Stix¹,

Layne²

1996

J. Geophys. Res.

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“…Indeed, having crystalline SiO 2 (cristobalite) in the groundmass of the most crystalline lava samples indicates that devitrification had begun in the flow core [ Figure 4; Damby 2012;Horwell et al 2013;Schipper et al 2015], and halogens are known to become mobile (F more so than Cl) during the devitrification of rhyolites [Stix et al 1995]. The salient point demonstrated by the data is that halogens do mobilise out of the melt during this late-stage evolution in the slowly cooled portions of the lava flow.…”

Section: Volatile Behaviour During Isobaric Crystallisationmentioning

confidence: 91%

“…Gualda and Ghiorso 2013]. This, and the observation that these samples contain groundmass cristobalite [ Figure 5A; Schipper et al 2015] suggests that these highly crystalline samples are starting to show compositional effects of devitrification [Lofgren 1970;Stix et al 1995;Rowe et al 2012]. The most notable changes with increasing groundmass crystallinity (and matrix glass SiO 2 ) are inflections in TiO 2 , CaO, Na 2 O and K 2 O at >77 wt.% SiO 2 (or >5 % microlites; Figure 6A).…”

Section: Major Elementsmentioning

confidence: 92%

“…Also, at high crystallinity (>75 %), Volcanica 2(1): 73 -90. doi: 10.30909/vol.02.01.7390 alkali mobility is apparent, with an inflection to decreasing K 2 O with increasing SiO 2 Figure 6B). This, as well as inflections in other major elements and halogens, may represent incipient devitrification of the lava matrix at high crystallinity [Lofgren 1970;Stix et al 1995;Rowe et al 2012;Schipper et al 2015]. Qualitatively, most lava samples have halogen concentrations below the maxima that would be expected if chlorine and fluorine behaved entirely incompatibly during isobaric microlite crystallisation ( Figure 7C-D, black dashed lines).…”

Section: Volatile Behaviour During Isobaric Crystallisationmentioning

confidence: 95%

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Halogen (Cl, F) release during explosive, effusive, and intrusive phases of the 2011 rhyolitic eruption at Cordón Caulle volcano (Chile)

Schipper

Castro²,

Kennedy

et al. 2019

Volcanica

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We investigate sulphur, chlorine and fluorine release during explosive, effusive and intrusive phases the 2011-2012 Cordón Caulle eruption, with a focus on the halogens. Analysis of melt inclusions, pyroclasts and lava samples shows most sulphur to have degassed during magma decompression, but halogen release to have accompanied isobaric crystallisation in slowly-cooled magma that was emplaced in a lava flow and sub-vent intrusion. Fluorine in particular mobilised only after extensive groundmass crystallisation and incipient devitrification. By 2017, gas emitted from vent-proximal fumaroles had hydrothermal compositions, with HCl/HF ratios correlating with temperature. We estimate that the eruption could eventually emit up to 0.92 Mt of SO 2 , 6.3 Mt of HCl, and 1.9 Mt of HF, but only ∼16 wt.%, ∼7 wt.% and ∼2 wt.% of these were respectively emitted during opening explosive phases. Halogen devolatilisation and its associated hazards can persist long after rhyolite eruption and/or emplacement.

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Fluorine

Koga

Rose-Koga

2016

Encyclopedia of Earth Sciences Series

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The behavior of light lithophile and halogen elements in felsic magma: geochemistry of the post-caldera Valles Rhyolites, Jemez Mountains Volcanic Field, New Mexico

Cited by 7 publications

References 29 publications

Gas saturation and evolution of volatile and light lithophile elements in the Bandelier magma chamber between two caldera‐forming eruptions

Gas saturation and evolution of volatile and light lithophile elements in the Bandelier magma chamber between two caldera‐forming eruptions

Halogen (Cl, F) release during explosive, effusive, and intrusive phases of the 2011 rhyolitic eruption at Cordón Caulle volcano (Chile)

Fluorine

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