Petrology of the alkali basalts in Mishima Island, Yamaguchi Prefecture, Southwest Japan with special reference to the primitive alkali basalt.

Nagasaki, Y.; Nagao, Takashi

doi:10.2465/ganko.83.191

Cited by 2 publications

(3 citation statements)

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“…The calculation was iterated until the composition of magma reaches Fe‐Mg equilibrium with the mantle olivine ( K D ≡ (Fe 2+ /Mg) melt /(Fe 2+ /Mg) olivine where its compositional dependency is corrected following Tamura et al, 2000). The forsterite content (Fo ≡ 100 × Mg/(Mg + Fe 2+ )) of the mantle olivine is assumed to be 89 as was found in most magnesian phenocrysts in mafic rocks in this district (Aoki, 1977; Higashiyama et al, 2013; Iwamori, 1989; Koyaguchi, 1986; Nagasaki & Nagao, 1988; Takahashi et al, 2017; Zellmer et al, 2014; Table S36) or predicted from the compositional relationship of olivine phenocrysts and spinel inclusions (Shukuno & Arai, 1999; Table S36). The ferric‐ferrous ratio (molar Fe 3+ /ΣFe) of primary magmas are assumed to be 0.15 using the empirical equation of Kelley and Cottrell (2009) with estimated H 2 O abundance of 1 wt% in primary magmas (discussed below).…”

Section: Discussionmentioning

confidence: 99%

“…Given that mafic minerals dominate liquidus phases in basaltic magmas (e.g., olivine, spinel, and clinopyroxene; Stolper, 1980), MgO content or Mg # of basaltic rock (SiO 2 < 56 wt%) is considered to represent the extent of magmatic differentiation. The Mg # of the studied samples varies from 78 to 40 (where Fe 3+ /Fe total (molar) = 0.15) and shows positive correlations with S15-S35; Feineman et al, 2013;Furuyama, 1976;Genbudo Research Group, 1991;Iwamori, 1989Iwamori, , 1991Iwamori, , 1992Kawamoto, 1990;Kimura, Gill, et al, 2014;Kurasawa & Takahashi, 1960;Moriyama, 2006;Morris et al, , 1999Nagao & Fujibayashi, 1989;Nagao & Sakaguchi, 1990;Nagasaki & Nagao, 1988;Pineda-Velasco et al, 2018;Sakiyama et al, 1995;Sawada et al, 2009;Sawada, Al-Jairani, et al, 2008;Sawada, Tome, et al, 2008;Shukuno & Arai, 1999;Takurayama Research Group, 1984;Tamura et al, 2000;Tatsumi et al, 1999;Uto, 1990;Yamauchi et al, 2009;Zellmer et al, 2015).…”

Section: Shallow-level Processesmentioning

confidence: 96%

“…Plot of Mg # (≡100 × Mg/(Mg + Fe 2+ ) in molar) versus CaO/Al 2 O 3 ratio (weight) and Cr-Ni abundances of mafic volcanic rocks in the Chugoku district. In Figure 5a, the literature data are shown as smaller symbols (TablesS15-S35;Feineman et al, 2013;Furuyama, 1976; Genbudo Research Group, 1991;Iwamori, 1989Iwamori, , 1991Iwamori, , 1992Kawamoto, 1990;Kimura, Gill, et al, 2014;Kurasawa & Takahashi, 1960;Moriyama, 2006;Morris et al, , 1999Nagao & Fujibayashi, 1989;Nagao & Sakaguchi, 1990;Nagasaki & Nagao, 1988;Pineda-Velasco et al, 2018;Sakiyama et al, 1995;Sawada et al, 2009;Sawada, Al-Jairani, et al, 2008;Sawada, Tome, et al, 2008;Shukuno & Arai, 1999; Takurayama Research Group, 1984;Tamura et al, 2000;Tatsumi et al, 1999;Uto, 1990;Yamauchi et al, 2009;Zellmer et al, 2015).Arrows with "pl", "ol", and "cpx" depict fractional crystallization of plagioclase, olivine, and clinopyroxene, respectively. Gray band indicates the range of Mg # of melt equilibrated with mantle olivine (Mg…”

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Feedback of Slab Distortion on Volcanic Arc Evolution: Geochemical Perspective From Late Cenozoic Volcanism in SW Japan

et al. 2020

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Southwest Japan is an island arc formed by subduction of the Philippine Sea (PHS) plate. The Quaternary magmatism in this region is characterized by eruptions of high-Sr andesites and dacites, considered to have been derived by melting of the PHS plate. The loci of these volcanoes spatially coincide with seismic discontinuities of the subducted PHS plate. Thus, the magmatism is interpreted as the result of slab melting at the plate tears. However, the processes that promote slab tearing remain unclear. In this study, we applied geochronological and geochemical analyses to late Cenozoic volcanic rocks in southwest Japan as tracers of slab morphology. Two different magma types, ocean-island basalt (OIB) and island-arc basalt (IAB), have occurred over 12 million years (Myr). These two magmas are attributed to different integrations of melts extracted from an originally fertile mantle; the OIBs from high temperature melt (1,300-1,400°C) were extracted at a depth of 40-80 km, whereas the IABs were extracted from a shallower, lower temperature region (30-60 km, 1,200-1,350°C). Secular change in Sr enrichment of IAB likely arose due to a transition of slab-derived fluids, incorporated into magmas as they formed, from water-to melt-dominant one. Progressive shallowing of the subducted PHS plate is responsible for secular change in the properties of slab-derived fluids as well as rollback of OIB volcanoes. Production of chemically variable magmas in the Chugoku district is the surface expression of distorting slab morphology by interaction between mantle and the subducting plate.

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Section: Discussionmentioning

confidence: 99%

Section: Shallow-level Processesmentioning

confidence: 96%

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Feedback of Slab Distortion on Volcanic Arc Evolution: Geochemical Perspective From Late Cenozoic Volcanism in SW Japan

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Zonal structure of Cenozoic basalts related to mantle upwelling in southwest Japan

Iwamori¹

1991

J. Geophys. Res.

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Cenozoic olivine‐bearing basaltic rocks in the central Chugoku district form eight provinces, each 20 to 30 km in diameter. These provinces can be grouped into three zones almost parallel to the elongation of the SW Japan arc, based on geological and petrological characteristics. The San‐yo zone (the closest to the Nankai trough) is characterized by a small amount of alkaline basalt. In the Sekiryo zone (intermediate zone), transitional basalt is dominant. The San‐in zone along the Japan Sea coast is characterized by subalkaline basalt and a large amount of andesitic rocks. The eruption volume of these volcanics exponentially increases toward the back arc side (less than 1 km3 to more than 100 km3). Chemical compositions of relatively undifferentiated basalts show systematic across‐arc variations. SiO2 and Al2O3increase, and FeO*, MgO and CaO decrease toward the back arc side (44 to 54, 13 to 18, 11 to 6, 13 to 7 and 12 to 8 wt % at FeO*/MgO=0.85, respectively). Melting experiments on the basalt‐H2O‐CO2 systems show that the pressure and temperature of magma segregation decrease toward the back arc side (17–19 kbar and 1340°–1320°C to 8 kbar and 1250°C), and the coexisting phases change from a spinel lherzolite assemblage to a harzburgite assemblage. These PT conditions define a trend which can be interpreted as a PT path for adiabatic upwelling of the mantle material. Consequently, the observed volcanism and zonation may have been caused by upwelling of a plume from a deep part of the mantle.

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Petrology of the alkali basalts in Mishima Island, Yamaguchi Prefecture, Southwest Japan with special reference to the primitive alkali basalt.

Cited by 2 publications

References 14 publications

Feedback of Slab Distortion on Volcanic Arc Evolution: Geochemical Perspective From Late Cenozoic Volcanism in SW Japan

Feedback of Slab Distortion on Volcanic Arc Evolution: Geochemical Perspective From Late Cenozoic Volcanism in SW Japan

Zonal structure of Cenozoic basalts related to mantle upwelling in southwest Japan

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