Origin of anorthite and olivine megacrysts in island-arc tholeiites: petrological study of 1940 and 1962 ejecta from Miyake-jima volcano, Izu-Mariana arc

Amma-Miyasaka, Mizuho; Nakagawa, Mitsuhiro

doi:10.1016/s0377-0273(02)00224-x

Cited by 34 publications

(17 citation statements)

References 45 publications

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“…The subsiding blocks might be highly fractured and the open fractures created by the subsidence likely provided pathways for the magma ascent. Existence of olivine and plagioclase cumulate has been suggested by Amma-Miyasaka and Nakagawa (2002) based on the findings of cumulate in previous eruption products of Miyakejima. Incorporation of the cumulate into the erupted materials might indicate that the cumulate locally distributed along the magma conduit above the shallow magma chamber.…”

Section: Magmatic Processes Of the 18 August 2000 Eruptionmentioning

confidence: 97%

Petrological characteristics and volatile content of magma from the 2000 eruption of Miyakejima Volcano, Japan

et al. 2005

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Among the series of eruptions at Miyakejima volcano in 2000, the largest summit explosion occurred on 18 August 2000. During this explosion, vesiculated bombs and lapilli having cauliflower-like shapes were ejected as essential products. Petrological observation and chemical analyses of the essential ejecta and melt inclusions were carried out in order to investigate magma ascent and eruption processes. SEM images indicate that the essential bombs and lapilli have similar textures, which have many tiny bubbles, crystal-rich and glass-poor groundmass and microphenocrysts of plagioclase, augite and olivine. Black ash particles, which compose 40% of the air-fall ash from the explosion, also have similar textures to the essential bombs. Whole-rock analyses show that the chemical composition of all essential ejecta is basaltic (SiO 2 =51-52 wt%). Chemical analyses of melt inclusions in plagioclase and olivine phenocrysts indicate that melt in the magma had 0.9-1.9 wt% H 2 O, <0.011 wt% CO 2 , 0.04-0.17 wt% S and 0.

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Section: Magmatic Processes Of the 18 August 2000 Eruptionmentioning

confidence: 97%

Petrological characteristics and volatile content of magma from the 2000 eruption of Miyakejima Volcano, Japan

et al. 2005

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“…It suggests that the summit bombs may have been produced without mixing with differentiated A-type and/or A 0 -type magma. Although the summit bombs are exceptionally porphyritic among the historical lavas, these phenocrysts are not xenocrysts like the M-type crystal-clots in the megacryst-bearing rocks (Amma-Miyasaka and Nakagawa 2002). This is because (1) the compositions of phenocrysts in the summit bombs are more Ca-poor and Mg-poor than those of the M-type clots and (2) clinopyroxene and olivine in these bombs can coexist with the host liquid (Fig.…”

Section: Petrological Features Of the 2000 Magmasmentioning

confidence: 99%

Magma plumbing system of the 2000 eruption of Miyakejima Volcano, Japan

2005

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During the 2000 eruption at Miyakejima Volcano, two magmas with different compositions erupted successively from different craters. Magma erupted as spatter from the submarine craters on 27 June is aphyric basaltic andesite (<5 vol% phenocrysts, 51.4-52.2 wt% SiO 2 ), whereas magma issued as volcanic bombs from the summit caldera on 18 August is plagioclase-phyric basalt (20 vol% phenocrysts, 50.8-51.3 wt% SiO 2 ). The submarine spatter contains two types of crystal-clots, A-type and A 0 -type (andesitic type). The phenocryst assemblages (plagioclase, pyroxenes and magnetite) and compositions of clinopyroxene in these clots are nearly the same, but only A 0 -type clots contain Ca-poor plagioclase (An < 70). We consider that the A 0 -type clots could have crystallized from a more differentiated andesitic magma than the Atype clots, because FeO*/MgO is not strongly influenced during shallow andesitic differentiation. The summit bombs contain only B-type (basaltic type) crystal-clots of Ca-rich plagioclase, olivine and clinopyroxene. The Atype and B-type clots have often coexisted in Miyakejima lavas of the period 1469-1983, suggesting that the magma storage system consists of independent batches of andesitic and basaltic magmas. According to the temporal variations of mineral compositions in crystal-clots, the andesitic magma became less evolved, and the basaltic magma more evolved, over the past 500 years. We conclude that gradually differentiating basaltic magma has been repeatedly injected into the shallower andesitic magma over this period, causing the andesitic magma to become less evolved with time. The mineral chemistries in crystal-clots of the submarine spatter and 18 August summit bombs of the 2000 eruption fall on the evolution trends of the A-type and B-type clots respectively, suggesting that the shallow andesitic and deeper basaltic magmas existing since 1469 had successively erupted from different craters. The 2000 summit collapse occurred due to drainage of the andesitic magma from the shallower chamber; as the collapse occurred, it may have caused disruption of crustal cumulates which then contaminated the ascending, deeper basalt. Thus, porphyritic basaltic magma could erupt alone without mixing with the andesitic magma from the summit caldera. The historical magma plumbing system of Miyakejima was probably destroyed during the 2000 eruption, and a new one may now form.

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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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Origin of anorthite and olivine megacrysts in island-arc tholeiites: petrological study of 1940 and 1962 ejecta from Miyake-jima volcano, Izu-Mariana arc

Cited by 34 publications

References 45 publications

Petrological characteristics and volatile content of magma from the 2000 eruption of Miyakejima Volcano, Japan

Petrological characteristics and volatile content of magma from the 2000 eruption of Miyakejima Volcano, Japan

Magma plumbing system of the 2000 eruption of Miyakejima Volcano, Japan

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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