Limits to Magma Mixing Based on Chemistry and Mineralogy of Pumice Fragments Erupted from a Chemically Zoned Magma Body

Vogel, Thomas A.; Ryerson, Frederick J.; Noble, Donald C.; Younker, Leland W.

doi:10.1086/629162

Cited by 19 publications

(11 citation statements)

References 37 publications

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“…The chemical variation and distribution of pumice fragments in the large, chemically zoned ash flow sheets from the Southwest Nevada Volcanic Field have been interpreted to represent eruptions from zoned magma bodies [Lipman et a!., 1966;Noble and Christiansen, 1974;Christiansen eta!., 1977;Smith, 1979;Hildreth, 1981;Broxton et al, 1989;Byers et al, 1989;Flood et al, 1989a;Schuraytz et al, 1989;Vogel et al, 1987Vogel et al, , 1989aWarren et al, 1989;.…”

Section: Zoned Ash Flow Sheets: Southwest Nevada Volcanic Fieldmentioning

confidence: 99%

Origin of compositional heterogeneities in tuffs of the Timber Mountain Group: The relationship between magma batches and magma transfer and emplacement in an extensional environment

Cambray¹,

Vogel²,

Mills³

1995

J. Geophys. Res.

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Compositionally zoned ash flow sheets provide convincing evidence for chemically zoned magma bodies. Most workers have assumed that the high-silica portions of these magma bodies evolved largely by differentiation processes that occurred within the magma chamber. However, chemical heterogeneities within some ash flow sheets are not consistent with these differentiation processes. The chemical variation of pumice fragments in the large volume (>1200 km3), Rainier Mesa ash flow sheet ranges from 55 to 76.3% silica. These pumice fragments occur in three distinct chemical groups. A low-and high-silica group is separated by a compositional gap at about 72% silica, and within the high-silica group there are two distinct populations based on trace element variations. There is little overlap between populations. These three magma types have been resident in same magma chamber at the same time and cannot be produced by any differentiation process of a single magma body. They must reflect discrete magma batches generated in the source area. Furthermore, the lower silica portion (<72% SiOn) of the Rainier Mesa ash flow sheet is chemically distinct from the lower silica portion of the overlying Ammonia Tanks ash flow sheet, even though they erupted within 200,000 years of each other. These ash flow sheets from the SW Nevada volcanic field are associated in time and place with Basin and Range extension, and all models for extension involve detachment surfaces that extend to great depth. A model for the relationship of these compositional heterogeneities and the regional extension involves (1) the generation of magma batches by either continuous melting of the source at different temperatures, or by melting of different sources, (2) the use of faults (shears) as conduits for transport of magma, and (3) the use of a dilatant releasing step on a detachment as storage chamber for the magma. We first address the evidence for separately generated magma batches and then propose a model for their coalescence in a single chamber prior to eruption. [ 1981 ], Baker and McBirney [ 1985], and Trial and Spera [ 1990]). In almost all cases, the inferred trends toward the topCopyright 1995 by the American Geophysical Union. Paper number 95JB00515 0148-0227/95/95JB-00515505.00 of these magma bodies are increasing silica content, together with decreasing temperature and phenocryst content. Because of the occurrence of compositionally distinct pumice fragments within the upper portions of many large-volume ash flow sheets from the Southwest Nevada Volcanic Field, Vogel et al. [ 1987, 1989a], Flood et al. [ 1989a], Schuraytz et al. [1989], and Mills [1991] concluded that discrete compositional layers existed in their parental magma chamber. Regardless of the exact spatial configuration of these compositionally discrete magmas in a chamber, most workers generally accept the fact that large-scale zoning or layering was common. Most of these workers have assumed that an initial magma body evolved, to a large extent, by in situ differentiation from ...

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Section: Zoned Ash Flow Sheets: Southwest Nevada Volcanic Fieldmentioning

confidence: 99%

Origin of compositional heterogeneities in tuffs of the Timber Mountain Group: The relationship between magma batches and magma transfer and emplacement in an extensional environment

Cambray¹,

Vogel²,

Mills³

1995

J. Geophys. Res.

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“…The coexistence of diverse composition magmas (basalt ‐ dacite ‐ rhyolite) within the same magmatic plumbing system is now well documented, and the importance of mixing for increasing and restricting compositional diversity has been demonstrated in a number of case studies [ Bacon , 1990; Green , 1988; Mahood and Halliday , 1988; Vogel et al ., 1987a]. McBirney et al .…”

Section: Convergent Marginsmentioning

confidence: 99%

Recent Developments in Igneous Petrology

Lesher

Baker

1991

Reviews of Geophysics

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“…In almost all cases, the inferred trends toward the top of these magma bodies are of increasing silica content and decreasing temperature and phenocryst content. Because of the occurrence of compositionally distinct pumice fragments within the upper portions of many ash flow sheets, Vogel et al [1987Vogel et al [ , 1989 [Mills and Fogel, 1988;Mills, 1991] Mills [1991] gives detailed chemistry of the phenoerysts for these tuffs. Temperatures, based on iron-titanium oxides, range from 760øC (high-silica samples) to 900øC (low-silica samples) for the Raim'er Mesa Tuff, and 730øC (high silica) to 900øC (low silica) for the Ammonia Tanks Tuff [Mills, 1991].…”

Section: Introductionmentioning

confidence: 99%

Melt inclusions from chemically zoned ash flow sheets from the Southwest Nevada Volcanic Field

Vogel¹,

Aines²

1996

J. Geophys. Res.

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The purpose of this paper is to determine whether melt inclusions from three well studied, compositionally zoned ash flow sheets from the Southwest Nevada Volcanic Field can be used to determine the evolution of the parent magma bodies. All samples are from the quenched, glassy pumice fragments that occur in the upper and lower portions of the Topopah Spring Tuff (68.7-78.7% SiO2), the Rainier Mesa Tuff (55.0-76.3% SiO2), and the Ammonia Tanks Tuff (57.5-76.3% SiO:) (all Si02 values anhydrous). Most of the melt inclusions in this study are in feldspar; a few are in quartz. There are large variations of volatile concentrations in melt inclusions within an individual phenocryst and large variations in melt inclusions in different phenocrysts within a pumice fragment. This finding demonstrates that the volatiles did not reequilibrate after the formation of the ash flow sheet. The volatile contents of most of these melt inclusions represent decompression and loss of some volatiles and therefore do not represent conditions at the time of entrapment. The presence of CO2 in many inclusions demonstrates that the magma evolved a gas phase in its preemption evolution. The nonvolatile chemical variations of the melt inclusions from the Rainier Mesa and Ammonia Tanks Tuffs are similar. Melt inclusions from the lower-silica pumice fragments show a wide range of chemical variation and monitor the liquid as it evolved. In both tuffs some melt inclusions are significantly more silica-rich than the matrix glass, and indicate mixing with a more evolved magma. Most melt inclusions from the high-silica pumice fragments from each of these rafts show little chemical variation and are similar to the matrix glass. The fact that no lower-silica melt inclusions occur in the high-silica pumice fragments supports the model that the highsilica magma did not evolve from the low-silica magma. The maximum H20 concentrations of inclusions in each pumice fragment from the Rainier Mesa and Ammonia Tanks Tuffs show a general positive correlation with SiO2 concentrations of the pumice fragment. No such relationship is observed with the Topopah Spring Tuff. Flood et al. [1989a] Schuraytz et al. [1989], and Mills [1991] concluded that discrete compositional layers existed in the Copyright 1996 by the American Geophysical Union. Papat number 95JB03252. 0148-0227/96/95 JB-03252505.00 magma chamber. Regardless of the exact configuration of the zoning in the magma body, it is generally accepted that largescale zoning or layering was common. Most workers agree [Fisher and $chmincke, 1984, p. 48] that "...the volcanological, chemical, and mineralogical evidence for volatile enrichment with/n the tops ofmost magma columns is overwhelm/ng." Most studies are based on the assuraption that these magma bodies evolved to a large extent by differentiation of originally homogeneous magma bodies. If indetxmdently derived magma batches, each with its own volatile concentration, coalesced to form zoned magma bodies, the distribution of volatiles in the magma body may b...

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Limits to Magma Mixing Based on Chemistry and Mineralogy of Pumice Fragments Erupted from a Chemically Zoned Magma Body

Cited by 19 publications

References 37 publications

Origin of compositional heterogeneities in tuffs of the Timber Mountain Group: The relationship between magma batches and magma transfer and emplacement in an extensional environment

Origin of compositional heterogeneities in tuffs of the Timber Mountain Group: The relationship between magma batches and magma transfer and emplacement in an extensional environment

Recent Developments in Igneous Petrology

Melt inclusions from chemically zoned ash flow sheets from the Southwest Nevada Volcanic Field

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