Crystal growth and nucleation in two large diabase dikes

Gray, Norman H.

doi:10.1139/e70-033

Cited by 45 publications

(21 citation statements)

References 5 publications

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“…For a few samples, porosity was determined from only one image, and so an error on the corresponding N T was not propagated. Crystal number densities in a few of the crystal-poor samples (Table 2) were determined using image analysis from back-scattered-electron images, following the methods of Sato (1995) and Gray (1970).…”

Section: Experimental and Analytical Methodsmentioning

confidence: 99%

Heterogeneous bubble nucleation on Fe-Ti oxide crystals in high-silica rhyolitic melts

Gardner

Denis

2004

Geochimica et Cosmochimica Acta

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Section: Experimental and Analytical Methodsmentioning

confidence: 99%

Heterogeneous bubble nucleation on Fe-Ti oxide crystals in high-silica rhyolitic melts

Gardner

Denis

2004

Geochimica et Cosmochimica Acta

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“…The plagioclase nucleation rate appears to have increased as crystallization proceeded while the pyroxene nucleation rate decreased. Gray (1970) reports similar changes in the relative nucleation rates of plagioclase and pyroxene from the margins of thick dikes towards their centers (pyroxene nucleation rates decrease more rapidly than plagioclase nucleation rates; plagioclase nucleation/pyroxene nucleation increases), resulting in ophitic and poikilitic textures in the cores of larger dikes. The textures and grainsizes in the diabase samples recovered on Legs 137 and 140 are compatible with crystallization in the cores of thick dikes or thin sills.…”

Section: Discussionmentioning

confidence: 74%

Grain-Size, Morphological, and Compositional Variations in Igneous Silicates in Medium-Grained Diabase from Hole 504B

Naslund¹

1995

Proceedings of the Ocean Drilling Program, 137/140 Scientific Results

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Samples recovered from Hole 504B during Leg 140 include a number of medium-grained, holocrystalline diabases that appear to represent the cores of thick dikes. The plagioclase and pyroxene in these samples occur in a variety of crystal morphologies. Plagioclase occurs as phenocrysts, microphenocrysts, elongate crystals, skeletal crystals, and branching radial clusters. Pyroxene occurs as phenocrysts, microphenocrysts, ophitic crystals, and poikilitic crystals. Plagioclase compositions became progressively poorer in anorthite and MgO and progressively richer in FeO as crystallization proceeded, while the average grain volume decreased and the aspect ratio of individual grains increased. Pyroxene compositions are largely independent of crystal morphology.The diabase dikes recovered from Hole 504B during Leg 140 appear to have crystallized in situ. Crystal compositions and morphologies are consistent with a rapid cooling rate and solidification times for individual dikes on the order of hours or days. The crystallization rate and nucleation rate of plagioclase lagged behind the cooling rate so that the degree of undercooling progressively increased as crystallization proceeded. Plagioclase crystal morphologies indicate much greater degrees of supersaturation than do pyroxene or olivine crystal morphologies. The 504B diabase magmas appear to have been emplaced with abundant preexisting pyroxene and olivine nuclei, but with few preexisting plagioclase nuclei. The suppression of plagioclase nucleation and crystallization relative to that of pyroxene and olivine could provide a mechanism by which the actual fractionation assemblage is more pyroxene-rich and plagioclase-poor than that predicted from thermodynamic models, or that observed in isothermal crystallization experiments.

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“…The number density was then converted from two dimensions (n a ) to three dimensions (n v ). The bubble number density in three dimensions is calculated by the formula given by Gray (1970):…”

Section: Textural Analysismentioning

confidence: 99%

Crystallization of microlites and degassing during magma ascent: Constraints on the fluid mechanical behavior of magma during the Tenjo Eruption on Kozu Island, Japan

2006

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Bubble and crystal textures provide information with regard to the kinetics of the vesiculation and crystallization processes. They also provide insights into the fluid mechanical behavior of magma in a conduit. We performed textural (bubble and crystal) and compositional analyses of pyroclasts that were obtained from the Tenjo pyroclastic flow, which resulted on account of the eruption in 838 A.D. on Kozu Island, about 200 km south of Tokyo, Japan. Pyroclasts in one flow unit (300∼2,060 kg/m 3 ; average density 1330 kg/m 3 ) can be classified into three types on the basis of vesicle textures. Type I pyroclasts have small isolated spherical bubbles with higher vesicularities (67-77 vol.%) and number density (10.8-11.7 log m −3 ). Type II pyroclasts have vesicularities similar to type I (61-69 vol.%), but most bubbles exhibit evidences of bubble coalescence, and lower number densities than type I (8.9-9.5 log m −3 ). Type III pyroclasts contain highly deformed bubbles with lower vesicularities (16-34 vol.%) and number densities (8.2-9.0 log m −3 ). The microlite volume fraction (DRE converted) also changes consistently across type I, type II, and type III as 0.06, 0.08, and 0.10-0.15, respectively. However, the number density of the microlites remains nearly invariant in all the pyroclast types. These facts indicate that the variation in the microlite volume fraction is controlled not by the number density (i.e., nucleation process), but by the size (i.e., growth process); the growth history of each type of microlite was different. Water content determinations show that the three types of pumices have similar H 2 O contents (2.6±0.2 wt%). This fact implies that all three types were Editorial responsibility J. Stix quenched at nearly the same depth (35±5 MPa, assuming that the magma was water-saturated) in the conduit. If the crystal sizes are limited only by growth time, a variation in this parameter can be related to the residence time, which is attributed to the flow heterogeneity in the conduit. By assuming a laminar Poiseuille-type flow, these textural observations can be explained by the difference in ascent velocity and shearing motion across the conduit, which in turn results in the differences in growth times of crystals, degrees of deformation, and bubble coalescence. Consequently, for crystals in the inner part of the conduit, the crystal growth time from nucleation to quenching is shorter than that near the conduit wall. The vesicle texture variation of bubbles in types I, II, and III results from the difference in the deformation history, implying that the effect of degassing occurred primarily towards the conduit wall.

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Crystal growth and nucleation in two large diabase dikes

Cited by 45 publications

References 5 publications

Heterogeneous bubble nucleation on Fe-Ti oxide crystals in high-silica rhyolitic melts

Heterogeneous bubble nucleation on Fe-Ti oxide crystals in high-silica rhyolitic melts

Grain-Size, Morphological, and Compositional Variations in Igneous Silicates in Medium-Grained Diabase from Hole 504B

Crystallization of microlites and degassing during magma ascent: Constraints on the fluid mechanical behavior of magma during the Tenjo Eruption on Kozu Island, Japan

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