Experimental Constraints on Plagioclase Crystallization during H2O- and H2O–CO2-Saturated Magma Decompression

Riker, Jenny M.; Cashman, Katharine V.; Rust, Alison; Blundy, Jonathan D.

doi:10.1093/petrology/egv059

Cited by 39 publications

(55 citation statements)

References 112 publications

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“…In more silicic systems it has been possible to perform continuous decompression experiments rather than single-step or multistep decompression experiments [Brugger and Hammer, 2010;Riker et al, 2015]. These experiments suggest that single-step decompression experiments are not able to reproduce the textures in the natural samples as the kinetics are not the same.…”

Section: Resultsmentioning

confidence: 99%

Mafic Plinian eruptions: Is fast ascent required?

Szramek

2016

JGR Solid Earth

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It has been hypothesized that for a Plinian eruption of mafic magma to occur, that magma must ascend rapidly from the chamber to cause it to fragment into a jet containing juvenile and nonjuvenile tephra. To determine how fast mafic Plinian magmas need to travel to the level of fragmentation, a number of decompression experiments were carried out on two hydrous mafic magmas, and the results are compared to the products of two well‐documented mafic Plinian eruptions: the basaltic andesite Fontana eruption of Masaya (Nicaragua) and the hawaiite 122 B.C. eruption of Etna (Italy). Comparison of natural and experimental textures shows that the Fontana eruption can be replicated in the lab at decompression rates between 0.1 MPa s−1 and 0.2 MPa s−1. This decompression rate is faster than any previously determined experimentally rate for more silicic eruptions. The hawaiite was unable to be reproduced in the lab. The natural groundmass is highly crystalline, which would have raised the viscosity of the initial melt by 1–2 orders of magnitude, which may not be enough to cause fragmentation.

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Section: Resultsmentioning

confidence: 99%

Mafic Plinian eruptions: Is fast ascent required?

Szramek

2016

JGR Solid Earth

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“…Furthermore, they have similar matrix glass compositions ( Table 2). Numerous studies have shown that decompression-driven growth on preexisting crystals is an important crystallization process in magmatic systems (K. Cashman, 1988;Martel & Schmidt, 2003;Riker, Cashman, Rust, & Blundy, 2015). This means that the T3 and T6 pumice are cognate, although they have somewhat different petrographic characteristics and may not have originated from a common magma chamber.…”

Section: Line Of Descent Of Comagmatic Evolutionmentioning

confidence: 99%

“…On the other hand, the high-An core is in equilibrium with the T6 glass and even the T6 whole-rock composition (Figure 4), and its composition is similar to that of the rim of the T6 plagioclase ( Figure 5). Numerous studies have shown that decompression-driven growth on preexisting crystals is an important crystallization process in magmatic systems (K. Cashman, 1988;Martel & Schmidt, 2003;Riker, Cashman, Rust, & Blundy, 2015). Volcanic rocks erupted from the same magma chamber exhibit systematic compositional variations in matrix glasses and melt inclusions in response to different crystallization processes under varied P-T conditions (e.g., Blundy & Cashman, 2001;K.…”

Section: Line Of Descent Of Comagmatic Evolutionmentioning

confidence: 99%

Petrology and mineralogy of pumice from the Iheya North Knoll, Okinawa Trough: Implications for the differentiation of crystal‐poor and volatile‐rich melts in the magma chamber

et al. 2018

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The Iheya North Knoll is a submarine hill that is covered with pumice in the Okinawa Trough. The petrology and mineralogy of the crystal‐poor rhyolitic pumice collected from two sampling sites (T3 and T6) on the knoll were analysed in this article. The T6 pumice, which contains some mafic minerals (e.g., clinopyroxene, orthopyroxene), is slightly more crystal‐rich (<5 vol.%) than the T3 pumice (<2 vol.%). However, both types of pumice are high‐potassium rhyolites with similar Nd isotopic ratios and rare earth element patterns, as well as similar glass compositions, which indicates that they may fall along a line of descent of comagmatic evolution. The T6 pumice contains some xenomorphic clinopyroxenes that are not in equilibrium with their whole‐rock composition, which suggests that the crystal‐poor melt was extracted from a more mafic source. The T3 pumice features a flow structure, and its matrix glass records higher Cl concentrations and a lower total mass than the T6 pumice, which implies that the T3 melt has a higher volatile content and lower viscosity. The distinct petrographic characteristics but similar matrix glass compositions of the T3 and T6 pumice suggest that the extracted melt was physically differentiated during ascent, with the more crystal‐poor and volatile‐rich T3 melt reaching a higher lever in the magma chamber. Meanwhile, simulation calculations indicate that the melt experienced near‐adiabatic decompression‐driven chemical differentiation, which led to the growth of sodium‐rich plagioclase but not quartz in the pumice.

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“…The rarity of superheating might be consistent with the complex subvolcanic structure of intermediate/silicic arc volcanos which are formed of a crystal‐mush column with a wide array of small melt‐rich reservoirs spanning the upper to lower crust, with crystal‐bearing melts stalling at different depths upon ascent. Indeed, this is illustrated by complex magmatic processes such as polybaric crystallization, mixing, mingling, assimilation, and remobilization, which can be identified by zoned and corroded minerals, variable volatile contents of phenocryst‐hosted glass inclusions, distinct pumice‐, and crystal populations, as well as geophysical, tomographic and deformation inversion techniques that are able to map subvolcanic melt reservoirs [ Blundy et al ., ; Chadwick et al ., ; Dahren et al ., ; Foroozan et al ., ; Lees , ; Reubi and Blundy , ; Riker et al ., ; Waite and Moran , ; Wright et al ., ].…”

Section: Discussionmentioning

confidence: 99%

Comb layering monitors decompressing and fractionating hydrous mafic magmas in subvolcanic plumbing systems (Fisher Lake, Sierra Nevada, USA)

McCarthy

Müntener

2016

JGR Solid Earth

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Understanding the dynamics of volcanic eruptions requires constraints on the processes of melt extraction in shallow magma reservoirs. This study focuses on the formation of intraplutonic igneous layering known as comb layers and orbicules within the Fisher Lake Pluton, Sierra Nevada. Comb layers are mineralogically and texturally diverse, ranging from plagioclase‐amphibole comb layers to plagioclase‐pyroxene and olivine comb layers. The majority of individual layers are related to the initiation of plagioclase nucleation and growth on preexisting host rocks and remobilized xenoliths. We use simple phase diagrams to illustrate the formation of comb layers through crystal fractionation along conduit walls and xenoliths, with plagioclase as the liquidus phase. Near‐adiabatic ascent of water‐undersaturated melts through the crust will lead to superheating and crystal resorption, which upon saturation of volatiles at shallow depth can induce heterogeneous nucleation of plagioclase. The rarity of orbicules and comb layers worldwide suggests that adiabatic decompression of crystal‐poor, moderately hydrous melts through the crust is rare. Most melts in intermediate/silicic volcanoes crystallize in multiple reservoirs within the crust prior to emplacement at shallow depth as crystal‐bearing melts. Comb layers and orbicules preserve evidence of multiple melt injections where a sequence of texturally and mineralogically similar comb layers and orbicules reflect the timescale of an individual melt pulse. Short timescales on the order of months to years for the growth of these sequences are estimated using experimental plagioclase growth rates and are interpreted as representing the lifetime of a melt injection within a long‐lived, subvolcanic melt extraction zone.

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Experimental Constraints on Plagioclase Crystallization during H₂O- and H₂O–CO₂-Saturated Magma Decompression

Cited by 39 publications

References 112 publications

Mafic Plinian eruptions: Is fast ascent required?

Mafic Plinian eruptions: Is fast ascent required?

Petrology and mineralogy of pumice from the Iheya North Knoll, Okinawa Trough: Implications for the differentiation of crystal‐poor and volatile‐rich melts in the magma chamber

Comb layering monitors decompressing and fractionating hydrous mafic magmas in subvolcanic plumbing systems (Fisher Lake, Sierra Nevada, USA)

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