Magmatic processes in the Bishop Tuff rhyolitic magma based on trace elements in melt inclusions and pumice matrix glass

Roberge, Julie; Wallace, Paul; Kent, Adam J.R.

doi:10.1007/s00410-012-0807-8

Cited by 39 publications

(72 citation statements)

References 31 publications

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“…Anderson et al (2000) thus argued that the inverted CO 2 vs. H 2 O trend is due to crystal settling during phenocryst growth in a large, convecting magma chamber, rather than the result of magma ascending through the crust. Roberge et al (2013) observed reversed trends in the variation in CO 2 contents of MI from the Bishop tuff similar to those observed by Anderson et al (2000). In contrast to Anderson et al (2000), Roberge et al (2013) interpreted the trends to indicate that a later, CO 2 -rich (deep) magma invaded the shallower, CO 2 -poor magma reservoir.…”

Section: Introductioncontrasting

confidence: 47%

An assessment of the reliability of melt inclusions as recorders of the pre-eruptive volatile content of magmas

Esposito

Hunter

Schiffbauer

et al. 2014

American Mineralogist

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Many studies have used melt inclusions (MI) to track the pre-eruptive volatile history of magmas. Often, the volatile contents of the MI show wide variability, even for MI hosted in the same phenocryst. This variability is usually interpreted to represent trapping of a volatile-saturated melt over some range of pressures (depths) and these data are in turn used to define a magma degassing path. In this study, groups of MI that were all trapped at the same time (referred to as a melt inclusion assemblage or MIA) based on petrographic evidence, were analyzed to test the consistency of the volatile contents of MI that were all trapped simultaneously from the same melt.MIA hosted in phenocrysts from White Island (New Zealand) and from the Solchiaro eruption on the Island of Procida (Italy) were analyzed by secondary ion mass spectrometry (SIMS). In most MIA, H 2 O, F, and Cl abundances for all MI within the MIA are consistent (relative standard errors <27%, with the exception of two MIA), indicating that the MI all trapped a melt with the same H 2 O, F, and Cl concentrations and that the composition was maintained during storage in the magma as well as during and following eruption. In several MIA, S abundances are consistent (relative standard errors <33%, with the exception of five out of 28 MIA). Conversely, CO 2 (White Island and Solchiaro MIA) showed wide variability in several MIA. The result is that some MIA display a wide range in CO 2 content at approximately constant H 2 O. Similar trends have previously been interpreted to represent degassing paths, produced as volatile-saturated melts are trapped over some significant pressure (depth) range in an ascending (or convecting) magma body. However, the CO 2 vs. H 2 O trends obtained in this study cannot represent degassing paths because the MI were all trapped at the same time (same MIA). This requires that all of the MI within the MIA trapped a melt of the same composition (including volatile content) and at the same temperature and pressure (depth). The cause of the variable concentration of CO 2 within some MIA is unknown, but may reflect micrometer-scale heterogeneities within the melt during trapping, heterogeneities within individual MI, post-entrapment crystallization within the MI, or C-contamination during sample preparation. These results suggest that trends showing variable CO 2 and relatively uniform H 2 O obtained from MI may not represent trapping of volatile-saturated melts over a range of pressure, and care must be taken when interpreting volatile contents of MI to infer magma degassing paths.Results of this study have been used to estimate the uncertainties in volatile concentrations of MI determined by SIMS analysis. The H 2 O, F, and Cl contents have an average estimated uncertainty of 11, 9, and 12%, respectively, which is consistent with the SIMS analytical error. In contrast, the S and CO 2 contents have an average estimated uncertainty of 24 and 69%, respectively, which is considerably larger than the SIMS analytical error.

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Section: Introductioncontrasting

confidence: 47%

An assessment of the reliability of melt inclusions as recorders of the pre-eruptive volatile content of magmas

Esposito

Hunter

Schiffbauer

et al. 2014

American Mineralogist

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show abstract

“…Most informative are detailed studies of phenocryst-hosted melt inclusions, which preserve dissolved volatiles that can be used to estimate entrapment pressures, and major and trace element compositions that can be used to track magma evolution. From a volcanological perspective, an interesting observation is that melt inclusion studies often indicate magma extraction from a large pressure range, even very early in the eruptive sequence (e.g., Wallace et al, 1999;Liu et al, 2006;Mangiacapra et al, 2008;Roberge et al, 2013). One explanation for this could be pre-eruptive mixing of crystals from throughout the magma storage region.…”

Section: Eruption Dynamicsmentioning

confidence: 95%

“…In CP eruptions, in contrast, partial involvement of the crystal framework is suggested by a transition during and after caldera collapse from initially crystal-poor magma to crystal-rich magma. The latter often contains both cognate glomerocrysts and antecrysts with melt inclusions that are more evolved in composition than the matrix glass (that is, from a cooler, or more evolved, part of the magma reservoir; Beddoe-Stephens et al, 1983;Wolff et al, 1999;Charlier et al, 2007;Saunders et al, 2010;Roberge et al, 2013).…”

Section: Caldera Collapsementioning

confidence: 98%

Calderas and magma reservoirs

Cashman

Giordano

2014

Journal of Volcanology and Geothermal Research

226

147

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Section: Rejuvenation Of the Bishop Magma Bodymentioning

confidence: 99%

“…Studies on melt inclusion entrapment pressures and compositions have however, shown that core and rim inclusions crystallised at comparable pressures, but within varying melt compositions (Wallace et al 1999;Roberge et al 2013). These observations imply that introduction of a melt with a slightly different composition underlies the growth of bright rims on quartz and sanidine Roberge et al 2013). The short timescales presented here support this hypothesis of shortly pre -1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 eruptive rejuvenation of lower parts of the Bishop magma chamber by interaction with a melt enriched in Ti, Ba, Sr and CO 2 (Wallace et al 1999;Hildreth and Wilson 2007;Wark et al 2007;Roberge et al 2013).…”

Section: Rejuvenation Of the Bishop Magma Bodymentioning

confidence: 99%

Timescales of mixing and mobilisation in the Bishop Tuff magma body: perspectives from diffusion chronometry

Chamberlain

Morgan

Wilson

2014

Contrib Mineral Petrol

135

173

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Abstract:We present two-feldspar thermometry and diffusion chronometry from sanidine, orthopyroxene and quartz from multiple samples of the Bishop Tuff, California, to constrain the temperature stratification within the pre-eruptive magma body and the timescales of magma mixing prior to its eruption. Two-feldspar thermometry yields estimates that agrees well with previous Fe-Ti oxide thermometry and gives a ~80 °C temperature difference between the earlier-and later-erupted regions of the magma chamber. Using this thermometry, we model diffusion of Ti in quartz, and Ba and Sr in sanidine as well as Fe-Mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on these phenocryst phases. Diffusion profiles of Ti in quartz and Fe-Mg in orthopyroxene diffusion both yield timescales of <150 years for the formation of overgrowth rims. In contrast, both Ba and Sr diffusion in sanidine yield nominal timescales 1-2 orders of magnitude longer than these two methods. The main cause for this discrepancy is inferred to be an incorrect assumption for the initial profile shape for Ba and Sr diffusion modelling (i.e., growth zoning). Utilising the divergent diffusion behaviour of Ba and Sr, we place constraints on the initial width of the interface and can refine our initial conditions considerably, bringing Ba and Sr data into alignment, and yielding timescales closer to 500 years, the majority of which are then within uncertainty of timescales modelled from Ti diffusion in quartz. Care must be thus taken when using Ba-in-sanidine geospeedometry in evolved magmatic systems where no other phases or elements are available for comparative diffusion profiling. Our diffusion modelling reveals piecemeal rejuvenation of the lower parts of the Bishop Tuff magma chamber at least 500 years prior to eruption. Timescales from our mineral profiling imply either that diffusion coefficients currently used are uncertain by 1-2 orders of magnitude, or that the minerals concerned did not experience a common history, despite being extracted from the same single pumice clasts. Introduction of the magma initiating crystallization of the contrasting rims on sanidine, quartz, orthopyroxene and zircon was prolonged, and may be a marker of other processes that initiated the Bishop Tuff eruption rather than the trigger itself. 2 AbstractWe present two-feldspar thermometry and diffusion chronometry from sanidine, orthopyroxene and quartz from multiple samples of the Bishop Tuff, California, to constrain the temperature stratification within the pre-eruptive magma body and the timescales of magma mixing prior to its eruption. Twofeldspar thermometry yields estimates that agree well with previous Fe-Ti oxide thermometry and gives a ~80 °C temperature difference between the earlier-and later-erupted regions of the magma chamber. Using this thermometry, we model diffusion of Ti in quartz, and Ba and Sr in sanidine as well as Fe-Mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on th...

show abstract

Magmatic processes in the Bishop Tuff rhyolitic magma based on trace elements in melt inclusions and pumice matrix glass

Cited by 39 publications

References 31 publications

An assessment of the reliability of melt inclusions as recorders of the pre-eruptive volatile content of magmas

An assessment of the reliability of melt inclusions as recorders of the pre-eruptive volatile content of magmas

Calderas and magma reservoirs

Timescales of mixing and mobilisation in the Bishop Tuff magma body: perspectives from diffusion chronometry

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