Anorthite megacrysts from island arc basalts

Kimata, Mitsuyoshi; Nishida, Norimasa; Shimizu, Masahiro; Saito, Shizuo; Matsui, Toshie; Arakawa, Yoji

doi:10.1180/minmag.1995.59.394.01

Cited by 35 publications

(28 citation statements)

References 37 publications

(32 reference statements)

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“…The nal re nement was carried out adopting a scheme of solid solution towards this component. It has been suggested tentatively that as the 'excess-Al-component' the Al(Al 3 Si)O 8 end-member is introduced into anorthite megacrysts from island arc basalts (Kimata et al, 1995). A negative correlation between Al-excess and Rb is shown in Fig.…”

Section: Chemistrymentioning

confidence: 91%

Refinement of the crystal structure of a synthetic non-stoichiometric Rb-feldspar

Kyono

Kimata

2001

Mineral. mag.

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The crystal structure of hydrothermally synthesized Rb-feldspar (monoclinic, space group C2/m, a = 8.839 (2) There are two geochemical implications from this refinement: (1) identification of both rubicline triclinic with (Al,Si) ordered distribution and synthetic monoclinic RbAlSi 3 O 8 with (Al,Si) disordered distribution implies that Rb cannot be one of factors disrupting the (Al,Si) ordered and disordered distributions in feldspars; and (2) natural and synthetic feldspars capable of accommodating the large cations tend to incorporate &Si 4 O 8 , excess Al and H 2 O components in their crystal structures.

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Section: Chemistrymentioning

confidence: 91%

Refinement of the crystal structure of a synthetic non-stoichiometric Rb-feldspar

Kyono

Kimata

2001

Mineral. mag.

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“…Fourier transform infrared spectroscopy of anorthite macrocrysts from island arc basalts has revealed the -CH 2 -stretching band, which disappeared on heating to Ϸ510 K (115). Hydrocarbons are present along with microcrystals of Cu metal in related anorthite macrocrysts (116). Other reported lattice-stabilized species include: CH 3 , C 2 H 5 , NO 2 , and O Ϫ (114).…”

mentioning

confidence: 99%

“…Significant substitution of B, Mg, P, Ti, Mn, Fe, Cu, Zn, etc., for Al and Si in the framework and of NH 4 in alkali sites of feldspars (112, 114) might be useful for provision of elements needed in biomolecules. Fourier transform infrared spectroscopy of anorthite macrocrysts from island arc basalts has revealed the -CH 2 -stretching band, which disappeared on heating to Ϸ510 K (115). Hydrocarbons are present along with microcrystals of Cu metal in related anorthite macrocrysts (116).…”

mentioning

confidence: 99%

Biochemical evolution. I. Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars

Smith

1998

Proc. Natl. Acad. Sci. U.S.A.

117

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Catalysis at mineral surfaces might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and photochemical gas reactions. Many ideas are implausible in detail because the proposed mineral surfaces strongly prefer water and other ionic species to organic ones. The molecular sieve silicalite (Union Carbide; ‫؍‬ Al-free Mobil ZSM-5 zeolite) has a three-dimensional, 10-ring channel system whose electrically neutral Si-O surface strongly adsorbs organic species over water. Three -O-Si tetrahedral bonds lie in the surface, and the fourth Si-O points inwards. In contrast, the outward Si-OH of simple quartz and feldspar crystals generates their ionic organophobicity. The ZSM-5-type zeolite mutinaite occurs in Antarctica with boggsite and tschernichite (Al-analog of Mobil Beta). Archean mutinaite might have become de-aluminated toward silicalite during hot/cold/wet/dry cycles. Catalytic activity of silicalite increases linearly with Al-OH substitution for Si, and Al atoms tend to avoid each other. Adjacent organophilic and catalytic Al-OH regions in nanometer channels might have scavenged organic species for catalytic assembly into specific polymers protected from prompt photochemical destruction. Polymer migration along weathered silicic surfaces of micrometer-wide channels of feldspars might have led to assembly of replicating catalytic biomolecules and perhaps primitive cellular organisms. Silica-rich volcanic glasses should have been abundant on the early Earth, ready for crystallization into zeolites and feldspars, as in present continental basins. Abundant chert from weakly metamorphosed Archaean rocks might retain microscopic clues to the proposed mineral adsorbent/catalysts. Other framework silicas are possible, including ones with laevo/dextro one-dimensional channels. Organic molecules, transition-metal ions, and P occur inside modern feldspars.

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“…High anorthite content of plagioclase phenocrysts (An > 90) is often reported in basaltic rocks from frontal-arc volcanoes (e.g. Kimata et al 1995;Amma-Miyasaka and Nakagawa 2002), suggesting that magmas erupting from frontal-arc volcanoes are H 2 Orich such as >3 wt.% H 2 O in basaltic melt from the Izu-Oshima volcano (Hamada and Fujii 2007). A major disadvantage of the plagioclase phenocryst hygrometers proposed thus far, however, is that they can be used only when the pressure, temperature, and compositions of coexisting plagioclase and melts are known.…”

Section: Introductionmentioning

confidence: 99%

Water content in arc basaltic magma in the Northeast Japan and Izu arcs: an estimate from Ca/Na partitioning between plagioclase and melt

Ushioda

Takáhashi

Hamada

et al. 2014

Earth, Planets and Space

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The variation in water content of arc basaltic magmas in the Northeast Japan arc and the Izu arc was estimated using a simple plagioclase phenocryst hygrometer. In order to construct a plagioclase phenocryst hygrometer optimized for arc basalt magmas, we have conducted high-pressure melting experiments of relatively primitive basalt from the Miyakejima volcano, a frontal-arc volcano in the Izu arc. As a result of the experiments, we found that the Ca/Na partition coefficient between plagioclase and hydrous basaltic melt increases linearly with an increase in H 2 O content in the melts. We then selected from literature geochemical data sets of relatively primitive basaltic rocks with no evidence of magma mixing and the most frequent Ca-rich plagioclase phenocrysts from 15 basaltic arc volcanoes including both frontal-arc and rear-arc volcanoes. In the 15 volcanoes studied, plagioclase phenocrysts of high anorthite content (An > 90) were commonly observed, whereas plagioclase phenocrysts in rear arc volcanoes usually had a lower anorthite content (90 > An > 80). In all volcanoes studied, the estimated H 2 O content of basaltic magma was at least 3 wt.% H 2 O or higher. The magmas of volcanoes located on the volcanic front have about 5 wt.% H 2 O in magma whereas those from the rear-arc side are slightly lower in H 2 O content.

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Anorthite megacrysts from island arc basalts

Cited by 35 publications

References 37 publications

Refinement of the crystal structure of a synthetic non-stoichiometric Rb-feldspar

Refinement of the crystal structure of a synthetic non-stoichiometric Rb-feldspar

Biochemical evolution. I. Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars

Water content in arc basaltic magma in the Northeast Japan and Izu arcs: an estimate from Ca/Na partitioning between plagioclase and melt

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