The effect of pre-existing crystals on the crystallization kinetics of a soda–lime-silica glass. The courtyard phenomenon

Fokin, Vladimir M.; Potapov, O. V.; Chinaglia, C.R.; Zanotto, Edgar Dutra

doi:10.1016/s0022-3093(99)00417-2

Cited by 31 publications

(19 citation statements)

References 4 publications

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“…Additionally, we observed a decrease in the crystal growth velocity with increasing heat treatment time or increasing crystallinity. The first EDS measurements indicated that the above-mentioned facts are caused by a difference in composition between glass and evolving solid solution crystals [16,17]. The formation of solid solutions is consistent with the phase diagram of a pseudo binary section CaO AE SiO 2 -Na 2 O AE SiO 2 [18].…”

Section: Introductionsupporting

confidence: 66%

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Mutant crystals in Na2O·2CaO·3SiO2 glasses

Fokin¹,

Potapov²,

Zanotto³

et al. 2003

Journal of Non-Crystalline Solids

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Section: Introductionsupporting

confidence: 66%

“…We have previously demonstrated that crystals grown in this stoichiometric glass at high temperatures dramatically hinder the formation of new crystals at low temperatures in their vicinity [16]. This effect was dubbed the ÔcourtyardÕ phenomenon.…”

Section: Introductionmentioning

confidence: 98%

Mutant crystals in Na2O·2CaO·3SiO2 glasses

Fokin¹,

Potapov²,

Zanotto³

et al. 2003

Journal of Non-Crystalline Solids

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“…Changes in the ''groundmass,'' defined here as the matrix melt plus new crystallization in the form of microlites or growth rims on phenocrysts, are the focus of this study. We used lightly crushed material rather than a fine powder to minimize exposure of zoned phenocryst cores to melt and to limit the creation of additional crystal-melt surface area that could enhance crystal growth at the expense of nucleation [Fokin et al, 1999].…”

Section: Experimental Methodsmentioning

confidence: 99%

An experimental study of the kinetics of decompression‐induced crystallization in silicic melt

2002

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[1] Experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression. Pinatubo dacite was held at 780°C, 220 MPa, f O2 = NNO + 2, H 2 O-saturated conditions for an equilibration period, decompressed to final pressures, P f , ranging from 175 to 5 MPa, and then held for 0.3-931 hours. According to the plagioclase liquidus curve in P H2O -T space for the relevant melt composition, these decompressions impose effective undercoolings, ÁT eff , of 34-266°C. Growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 P f < 150 MPa (ÁT eff = 34-93°C), and equilibrium crystal modes are achieved in <168 hours. Microlite nucleation is the dominant transformation process for 10 < P f < 50 MPa (ÁT eff = 125-241°C), and chemical equilibrium is not attained by 168 hours under these conditions. Slow, steady decompressions typically produced normally zoned, euhedral, and planar-faceted feldspar crystals, although anhedral morphologies were produced at very low P f . Contrary to expectation, slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure. Although counterintuitive, these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth (controlled by ÁT eff and melt viscosity) experienced during each decompression path. Analysis of liquid to solid transformation kinetics using TTT-style diagrams shows that crystallization occurs most rapidly at $100 MPa by a crystal growth mechanism. The next most efficient crystallization conditions are at 25 MPa, in a crystal nucleationdominated regime.INDEX TERMS: 3630 Mineralogy and Petrology: Experimental mineralogy and petrology, 3640 Mineralogy and Petrology: Igneous petrology, 8434 Volcanology: Magma migration, 8439 Volcanology: Physics and chemistry of magma bodies;

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“…Small phenocryst fragments did not dissolve completely during 3-5 day runs at 900°C and 125 MPa, our determined preeruptive starting conditions. This introduces larger crystal melt boundaries than in the natural magma before ascent, which will enhance crystal growth at the expense of nucleation (Fokin et al 1999). Thus, preparation of starting material for decompression consisted of superheating the powder at 900°C and 200 MPa for 2-3 days, ensuring that most of the phenocryst fragments are dissolved.…”

Section: Decompression Experimentsmentioning

confidence: 99%

Experimental constraints on syneruptive magma ascent related to the phreatomagmatic phase of the 2000AD eruption of Usu volcano, Japan

2006

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We experimentally studied the dacitic magma ejected during the first event in the Usu 2000 eruption to investigate the conditions of syneruptive magmatic ascent. Geophysical data revealed that the magma reached under West Nishiyama, the location of the event's craters, after rising beneath the summit. Prior study of bubble-size distributions of ejecta shows two stages (stage 1 and stage 2) with different magma ascent rates, as the magma accelerated beneath West Nishiyama with the start of the second stage. To simulate ascent of stage 1 from the main reservoir, which was located at a depth of 4-6 km (125 MPa) to 2 km (50 MPa) beneath West Nishiyama, decompression experiments were conducted isothermally at 900°C following two paths. Single step decompression (SSD) samples were decompressed rapidly (0.67 MPa/s) to their final pressure and held for 12 to 144 hours. Multiple step decompression (MSD) samples were decompressed stepwise to their final pressure and quenched instantly. In MSD, the average decompression rates and total experimental durations varied between 0.01389 to 0.00015 MPa/s and 1.5 to 144 hours, respectively. Syneruptive crystallization was confined to stage 1, and the conditions of ascent were determined by documenting similarities in decompression-induced crystallization between ejecta and experiments. Core compositions, number densities, and shapes of experimental microlites indicate that ascent to 2 km depth occurred in less than 1.5 h. Volumes and number densities of experimental microlites from the SSD experiments that best replicate the decompression rate to 2 km indicate that the magma remained at 2 km for approximately 24 h before the eruption. Stagnation at a depth of 2 km corresponds with horizontal transport through a dike from beneath the summit to West Nishiyama, according to geodetic results. The total magma transport timescale including stage 2 is tens of hours and is shorter than the timescale of precursory seismicity (3.5 days), indicating that the erupted magma did not move out of the reservoir for the first 2 days. This is consistent with the temporal change in numbers of earthquakes, which reached a peak after 2 days.

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The effect of pre-existing crystals on the crystallization kinetics of a soda–lime-silica glass. The courtyard phenomenon

Cited by 31 publications

References 4 publications

Mutant crystals in Na2O·2CaO·3SiO2 glasses

Mutant crystals in Na2O·2CaO·3SiO2 glasses

An experimental study of the kinetics of decompression‐induced crystallization in silicic melt

Experimental constraints on syneruptive magma ascent related to the phreatomagmatic phase of the 2000AD eruption of Usu volcano, Japan

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