Olivine-chromian spinel compositional relationships of the Cenozoic alkali basalts from Southwest Japan: implication for their mantle restites.

浩司, 宿野; 章司, 荒井

doi:10.2465/ganko.94.120

Cited by 9 publications

(7 citation statements)

References 26 publications

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“…Later magmatism (6–0 Ma) is characterized by eruptions of geochemically variable rocks. These rocks consist of subalkaline basalt and andesite including magnesian andesite (nonadakitic) and alkaline basalts with ultrasodic and ultrapotassic suites (Iwamori, ; Kimura et al, ; Koyaguchi, ; Nakamura et al, ; Shukuno & Arai, ; Tatsumi et al, ). In particular, the magmatism in the last 2 Myr is dominated by voluminous emplacement of high‐Sr andesites and dacites (adakitic; Kimura et al, ; Figure ).…”

Section: Tectonic and Geologic Backgroundmentioning

confidence: 99%

Production of High‐Sr Andesite and Dacite Magmas by Melting of Subducting Oceanic Lithosphere at Propagating Slab Tears

et al. 2018

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We present K-Ar ages, major and trace element concentrations, and Sr-Nd-Pb isotope data for late Cenozoic volcanic rocks from the Chugoku district, southwest Japan arc. Andesite and dacite lavas in this region are enriched in Sr (mostly >800 μg g À1 ) and show geochemical characteristics of volcanic rocks commonly referred to as "adakite." K-Ar dating of these lavas revealed that the eruption of high-Sr andesitic to dacitic magmas occurred during the last 2 Myr, following or concurrent with the eruption of basalt in adjacent regions. Trace-element characteristics of high-Sr andesites and dacites are consistent with the formation of their parent magmas by partial melting of the basaltic layer of the subducting Shikoku Basin Plate. Mass balance modeling of trace element concentrations and isotopic compositions suggests that the parental magmas of high-Sr andesites and dacites are best explained by mixing of partial melts from oceanic crust (F = 5-15%) and sediment (F = 30%) at 80:20 to 55:45 ratios. Spatial coincidence of the occurrences of high-Sr andesites and dacites and seismic gaps of the subducting slab demonstrates the causal link between slab melting and mantle upwelling at slab tears. We speculate that these tears could have been formed by subduction of ridges on the plate. A warm mantle upwelled through tears, preventing the solidification of the siliceous slab melts in the mantle and facilitating the transportation of these melts to the surface.The southwest (SW) Japan arc (Figure 1) is an example of a volcanic field in which high-Sr andesites and dacites occur (Figure 2;Feineman et al., 2013;Kimura et al., 2014;Morris, 1995). Like others, the SW Japan arc is characterized by the occurrence of basalt lavas in closed spatial and temporal proximity. It is PINEDA-VELASCO ET AL.3698

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Section: Tectonic and Geologic Backgroundmentioning

confidence: 99%

Production of High‐Sr Andesite and Dacite Magmas by Melting of Subducting Oceanic Lithosphere at Propagating Slab Tears

et al. 2018

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“…The chromian spinel is relatively low in TiO 2 (<1 wt %), and plotted around the boundary between intraplate and arc magmas in the TiO 2 -Y Fe space [66]. The Bankawa alkali basalt shows a very primitive character in terms of the Fo (olivine)-Cr# (spinel) relationship [41,67,68] (Figure 8). Some of the olivine-spinel pairs in the host rock are plotted in or near the olivine-spinel mantle array, a residual spinel peridotite field (Figure 8) [41,67].…”

Section: Chemistry Of the Host Rockmentioning

confidence: 99%

Abyssal Peridotite as a Component of Forearc Mantle: Inference from a New Mantle Xenolith Suite of Bankawa in the Southwest Japan Arc

et al. 2018

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Lithology and petrologic nature of the forearc mantle have been left unclear due to the very limited sampling to date. Here, we present petrological data on a forearc peridotite suite obtained as xenoliths in an alkali basalt dike (7.5 Ma) from the Bankawa area in the Southwest Japan arc for our better understanding of the forearc mantle. The host alkali basalt is of asthenosphere origin, and passed through a slab window with slight chemical modification by the slab-derived component. The Bankawa peridotite suite is comprised of lherzolites, which contain various amounts of secondary phlogopite and were metasomatized to various degrees. The least metasomatized lherzolite exhibits Fo91 of olivine, Cr/(Cr + Al) = 0.3 of chromian spinel, and depletion of middle to light rare-earth elements in clinopyroxene, and is overall similar to an abyssal lherzolite. It had originally formed at the proto-Pacific Ocean and then was trapped at a eastern margin of Eurasian continent by initiation of subduction. The forearc mantle peridotite formed as a residue of proto-arc magma formation is depleted harzburgite as represented by the peridotites obtained from the forearc seafloor, but can be less depleted abyssal peridotite if being devoid of partial melting or reaction with magmas after entrapment.

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“…The previous studies (Kimura, Gill, et al, 2014; Pineda‐Velasco et al, 2018; Sakuyama, Nakai, et al, 2014; Sakuyama et al, 2009) assumed that the magma source beneath SW Japan has trace‐element composition and mineralogy of the primitive (upper) mantle (PUM; McDonough & Rudnick, 1998; Sun & McDonough, 1989). This assumption is based on the predominance of fertile peridotites (clinopyroxene‐rich lherzolites) in xenoliths hosted in OIB (Arai & Muraoka, 1992) and chondritic‐REE patterns of clinopyroxene in these xenoliths (Abe et al, 1998), as well as low Cr/(Cr + Al) of spinel inclusions (<0.5 in molar) in forsteritic olivine phenocrysts (Fo > 85) in OIB (Shukuno & Arai, 1999); all of these features indicate that the mantle beneath the Chugoku district is fertile.…”

Section: Discussionmentioning

confidence: 99%

“…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).…”

Section: Approach 1: Geothermobarometrymentioning

confidence: 99%

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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Olivine-chromian spinel compositional relationships of the Cenozoic alkali basalts from Southwest Japan: implication for their mantle restites.

Cited by 9 publications

References 26 publications

Production of High‐Sr Andesite and Dacite Magmas by Melting of Subducting Oceanic Lithosphere at Propagating Slab Tears

Production of High‐Sr Andesite and Dacite Magmas by Melting of Subducting Oceanic Lithosphere at Propagating Slab Tears

Abyssal Peridotite as a Component of Forearc Mantle: Inference from a New Mantle Xenolith Suite of Bankawa in the Southwest Japan Arc

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

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