研究者データベース

栗谷 豪(クリタニ タケシ)
理学研究院 地球惑星科学部門 地球惑星システム科学分野
教授

基本情報

所属

  • 理学研究院 地球惑星科学部門 地球惑星システム科学分野

職名

  • 教授

学位

  • 博士(理学)(東京大学)

ホームページURL

J-Global ID

研究キーワード

  • マグマ   火山   マントル   時間スケール   マグマ溜まり   熱進化   地球化学   マグマ溜り   利尻火山   モデル化   U-Th放射非平衡   地殻・マントル   水循環   地殻   岩石学   マグマ進化   国際情報交換   地質学   桜島火山   衛星データー解析   白頭山   噴火様式   鉱物   気泡形状緩和   マグマの浸透率   岩石化学   CO2フラクシング   ブルカノ式噴火   浅間火山   磁鉄鉱   

研究分野

  • 自然科学一般 / 固体地球科学

職歴

  • 2015年 北海道大学 理学(系)研究科(研究院) 准教授

学歴

  •         - 2000年   東京大学   理学系研究科   地質学
  •         - 2000年   東京大学
  •         - 1995年   東京大学   理学部   地学科
  •         - 1995年   東京大学

所属学協会

  • Geochemical Society   アメリカ地球物理学連合   日本火山学会   日本岩石鉱物鉱床学会   

研究活動情報

論文

  • Hajime Taniuchi, Takeshi Kuritani, Tetsuya Yokoyama, Eizo Nakamura, Mitsuhiro Nakagawa
    Scientific Reports 10 1 2020年12月01日 [査読有り][通常論文]
     
    © 2020, The Author(s). Felsic magmas produced at subduction zones have played an important role in the generation and evolution of the continental crust. For the origin of felsic magmas, processes such as fractional crystallization of mafic magmas, partial melting of crustal materials, partial melting of subducting slabs, and partial melting of pyroxenitic mantle wedge components have been proposed. Recent experimental studies have predicted that felsic melt can also be produced in the mantle wedge by the separation of slab-derived supercritical liquid beyond depths corresponding to the critical point. To date, however, the presence of felsic magma of this origin has not yet been reported. In this study, we investigated dacitic lavas and preceding calc-alkaline andesite lavas from the Rishiri Volcano, located at the rear of the Kuril arc. We show that hydrous felsic melt and aqueous fluid were separated from slab-derived supercritical liquid in the mantle wedge. The former erupted as dacitic magma whilst the aqueous fluid induced the generation of primary basaltic magma involved in creating calc-alkaline andesite magma. We infer that slab-derived supercritical liquid is an efficient transport medium for moving silicate-rich components from subducting slabs to the Earth’s surface, and that this process may have contributed to the growth of the continental crust.
  • Takeshi Kuritani, Mitsuhiro Nakagawa, Jumpei Nishimoto, Tetsuya Yokoyama, Tsuyoshi Miyamoto
    Lithos 366-367 2020年08月 [査読有り][通常論文]
     
    © 2020 Elsevier B.V. A caldera-forming eruption in 946 CE, known as the Millennium Eruption (ME), at Changbaishan (or Baekdusan) volcano, located on the border between China and North Korea, was one of the largest explosive eruptions on Earth in the last 2000 years. In this study, we obtained new whole-rock Sr, Nd, and Pb isotopic data and 238U–230Th disequilibrium data of representative volcanic products of the ME, as well as those of a pre-ME (4–5 ka) eruption, to understand the evolution of the magma plumbing system related to the caldera-forming eruption. The volcanic products of the ME have SiO2 contents ranging from ~54 to ~75 wt%, and the whole-rock (230Th/232Th) ratios tend to decrease systematically from basaltic trachy-andesite through trachyte to comendite. The relatively high (230Th/232Th) ratios of the felsic (trachytic and comenditic) volcanic products suggest that they were formed primarily from fractional crystallization of mafic magmas, rather than from partial melting of crustal materials. The basaltic trachy-andesite sample has a distinctly high (230Th/232Th) ratio and the least radiogenic Pb isotopic ratios among ME volcanic products, suggesting that the mafic magma was recently introduced into the main felsic magma system and is hypothesized to have triggered the eruption. The lower (230Th/232Th) ratios of the comendite samples than those of the trachyte samples, as well as published U-series disequilibrium data, suggest that the comendite magmas were produced by mixing old (> ~ 23 ka) and young (<~6 ka) comenditic magmas. The old comendite magma was the main component of ME volcanic products. Pre-ME pantelleritic magmas with distinctly low (230Th/232Th) and high 87Sr/86Sr ratios from those of ME magmas may have formed a short-lived magma chamber until ~4–5 ka, which was isolated from the long-lived, main comendite magma chamber.
  • Chihiro Ishii, Yoshinori Ikenaka, Shouta M M Nakayama, Takeshi Kuritani, Mitsuhiro Nakagawa, Keisuke Saito, Yukiko Watanabe, Kohei Ogasawara, Manabu Onuma, Atsushi Haga, Mayumi Ishizuka
    The Journal of veterinary medical science 2020年06月18日 [査読有り][通常論文]
     
    Birds of a number of species have died as a result of lead (Pb) poisoning, including many Steller's sea eagles (Haliaeetus pelagicus) and white-tailed sea eagles (Haliaeetus albicilla) in Hokkaido, the northernmost island of Japan. To address this issue, the use of any type of Pb ammunition for hunting of large animals was prohibited in Hokkaido in 2004. However, Pb poisoning is still being reported in this area, and there are few regulations regarding the use of Pb ammunition in other parts of Japan, where it has been reported that eagles and water birds have been exposed to Pb. This study was performed to accurately determine the current level of Pb exposure of birds found dead in the field or dead in the wild bird centers in Japan (June 2015-May 2018) and to identify the sources of Pb. Pb exposure was found to still be occurring in raptors and water birds in various parts of Japan. 26.5% and 5.9% of the recorded deaths of Steller's sea eagles and white-tailed sea eagles, respectively, were found to have been poisoned by Pb. In addition, Pb isotope ratio analysis showed that both Pb rifle bullets and Pb shot pellets cause Pb exposure in birds, and these endangered eagles are also exposed to Pb in Hokkaido due to the illegal use of Pb ammunition. Changing to Pb-free ammunition, such as copper (Cu) rifle bullets, steel shot pellets, or bismuth shot pellets, will be essential for the conservation of avian species in Japan.
  • Haruya Toyomaki, John Yabe, Shouta M.M. Nakayama, Yared B. Yohannes, Kaampwe Muzandu, Allan Liazambi, Yoshinori Ikenaka, Takeshi Kuritani, Mitsuhiro Nakagawa, Mayumi Ishizuka
    Chemosphere 247 2020年05月 [査読有り][通常論文]
     
    © 2020 Lead (Pb)-poisoning is a serious public health concern and dogs have been useful as a sentinel-animal for Pb exposure of humans. In the present study, the blood Pb concentrations (BLC), isotope ratios (208 Pb/206 Pb and 207 Pb/206 Pb), and biochemistry of 120 domestically owned dogs living around a Pb mining area, in Kabwe, Zambia were analyzed to determine factors associated with Pb exposure. The overall mean value of Pb in dog blood in the present study was 271.6 μg/L. The BLC in the dogs from sites near the mine were significantly higher than those in the dogs from a site 4 km from the mine (352.9 ± 205.1 μg/L versus 28.0 ± 13.9 μg/L). BLC significantly decreased with both increasing age of the dogs and distance from the mine. The Pb isotope ratios in the dog that resided near the mine showed values similar to those reported at the galena mine in Kabwe, which is considered to be the source of Pb exposure. In contrast to the high metal exposure that was determined in these dogs, the mean values of most analyzed parameters in the blood biochemical analysis were surprisingly within or close to the standard reference values. Moreover, none of the dogs showed overt signs of Pb-poisoning or other clinical symptoms. The results of analysis of Pb exposure of the dogs obtained in the present study, which are similar to the previously reported results in human in this location, suggest that dogs could be useful as a sentinel animal for Pb exposure of humans in Kabwe.
  • Hajime Taniuchi, Takeshi Kuritani, Mitsuhiro Nakagawa
    Lithos 354-355 2020年02月 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. Calc-alkaline andesite is a typical rock series in many island and continental arcs, and it commonly coexists with tholeiitic series rocks in individual volcanoes. In this study, the main controlling factors on the occurrence of calc-alkaline magmatism are examined for andesitic lavas from Rishiri Volcano, northern Japan. The whole-rock SiO2 contents of lavas range from 57.9 wt% to 61.9 wt%, and they are classified as calc-alkaline series. The lavas have petrographical and mineralogical features that show evidence of magma mixing. The whole-rock compositional variations of the lavas indicate that three end-member magmas were involved in their generation, a primitive mafic end-member magma, an evolved mafic end-member magma, and a felsic end-member magma. We suggest that the primitive mafic end-member magma represents a near primary magma generated in the upper mantle, the evolved mafic end-member magma was derived from the primitive magma by olivine fractionation, and the felsic end-member magma was produced primarily by partial melting of the crust. The primitive end-member magma is estimated to contain ~5 wt% water, which is much higher than those of the primary basaltic magmas of other volcanic stages of Rishiri that do not include calc-alkaline magmas. Based on this observation, we suggest that the water content of the primary magma was the main factor controlling the genesis of calc-alkaline magmatism at Rishiri. The more hydrous the primary magma and its derivative magma, the more extensive the melting of the crust due to the higher water flux from the solidifying magma chamber.
  • A. N.E. Asaah, T. Yokoyama, F. T. Aka, H. Iwamori, T. Kuritani, T. Usui, M. Gountie Dedzo, J. Tamen, T. Hassegawa, E. M. Fozing, M. J. Wirmvem, A. L. Nche
    Journal of African Earth Sciences 161 2020年01月 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd This study presents major elements, trace elements and Sr–Nd–Pb isotope data for fifteen (15) representative volcanic rock samples from volcanic edifices of Lakes Barombi Mbo (n = 9) and Barombi Koto (n = 6), located in the Kumba graben along the Cameroon Volcanic Line (CVL). The samples are dominantly basalts and trachy-basalts with MgO ranging from 7 to 9 wt.%. The lavas from the edifice of Lake Barombi Mbo are slightly richer in TiO2 (mean 3.3 wt%) and lower in CaO (mean 9.2 wt%) relative to those from the edifice of Lake Barombi Koto (2.9 wt% and 10.3 wt%, respectively). Trace element characteristics of the lavas suggest an enrichment of the source by carbonatitic metasomatism and melting of a heterogeneous source at varying depth in the garnet-spinel transition zone. Trace elements and isotopic composition of the lavas suggest insignificant crustal contamination. Modelling of the degree of partial melting suggest that the magmas were formed at varying depth (60–80 km) and by ~2% partial melting of a source containing less than 4% garnet. Samples from Lake Barombi Mbo formed at a higher degree of partial melting (2%–0.5%) and at a shallower depth relative to those from the volcanic edifice of Lake Barombi Koto (mostly <0.5%) and Mt. Cameroon. Interestingly, the relationship of Zr/Hf and 206Pb/204Pb suggests that the magma was affected by carbonatitic metasomatism whose effect decreased from Mt. Cameroon to Lake Barombi Mbo. Our results suggest that Lakes Barombi Mbo and Barombi Koto lavas are typical of lavas with HIMU-like signature and involved contributions from a dominantly sublithospheric mantle (SLM) and minor contributions from the sub-continental lithospheric mantle (SCLM). The SLM material rose and was hosted in the SCLM prior to melting.
  • Takeshi Kuritani, Qun Ke Xia, Jun Ichi Kimura, Jia Liu, Kenji Shimizu, Takayuki Ushikubo, Dapeng Zhao, Mitsuhiro Nakagawa, Shumpei Yoshimura
    Scientific Reports 9 1 2019年12月01日 [査読有り][通常論文]
     
    © 2019, The Author(s). Magmatism at some intraplate volcanoes and large igneous provinces (LIPs) in continental areas may originate from hydrous mantle upwelling (i.e. a plume) from the mantle transition zone (MTZ) at 410–660 km depths in the Earth’s deep interior. However, the ultimate origin of the magmatism, i.e. why mantle plumes could have been generated at the MTZ, remains unclear. Here, we study the buoyancy of a plume by investigating basalts from the Changbaishan volcano, beneath which a mantle plume from the hydrous MTZ is observed via seismology. Based on carefully determined water contents of the basalts, the potential temperature of the source mantle is estimated to be 1310–1400 °C, which is within the range of the normal upper mantle temperature. This observation suggests that the mantle plume did not have a significant excess heat, and that the plume upwelled because of buoyancy resulting from water supplied from the Pacific slab in the MTZ. Such a hydrous mantle plume can account for the formation of extremely hydrous LIP magmatism. The water was originally sourced from a stagnant slab and stored in the MTZ, and then upwelled irrespective of the presence or absence of a deep thermal plume.
  • Shumpei Yoshimura, Takeshi Kuritani, Akiko Matsumoto, Mitsuhiro Nakagawa
    Scientific Reports 9 1 2019年12月01日 [査読有り][通常論文]
     
    © 2019, The Author(s). Volatile-rich silicic magma erupts either explosively as a jet of a mixture of pyroclasts and high-temperature gas, or non-explosively to effuse lava. The bifurcation of the eruption style is widely recognised as being controlled by the efficiency of open-system gas loss from vesiculated magma during ascent. However, the fundamental question of how the gas escapes from highly viscous magma still remains unsolved because the pathways of gas flow are rarely preserved in dense lava. Here we show that such pathways are visualised in groundmass glass using high-resolution chlorine (Cl) mapping analysis on the rhyolitic lava of the Mukaiyama volcano, Japan. The results showed that the glass was highly heterogeneous in Cl content. A spatial distribution of the Cl content in the groundmass glass showed that volatiles diffused towards most bubbles, but the bubbles collapsed into the dense melt rather than growing. All observations, in combination with melt inclusion analysis, indicate that vesiculation, the formation of interconnected bubble channels, open-system gas loss via the channels, and channel collapse repeated within the period of a few days to two weeks during ascent. This cycle repeated individually in centimetre-sized portions of magma with different timing.
  • Takeshi Kuritani, Chizuko Kanai, Shigeru Yamashita, Mitsuhiro Nakagawa
    Lithos 348-349 2019年12月01日 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. Akita-Komagatake is an active volcano in the Northeast Japan arc with a slab depth (H) of ~110 km. In this study, magma generation conditions were estimated for basaltic products from the volcano to examine the thermal structure of the sub-arc mantle and the across-arc variations in the parameters related to magma genesis. The studied basalts have the highest MgO content (~6 wt%) among the products from the volcano and contain ~15% plagioclase phenocrysts, ~5% olivine phenocrysts, and <1% pyroxene phenocrysts. The water content of the melt was estimated to be ~4 wt% by melt inclusions in the phenocrysts using plagioclase–melt hygrometry. Multi-component thermodynamic analyses suggest that the primary magma was generated by ~14% melting of the source mantle with ~0.5 wt% H2O at ~1275 °C and ~1.3 GPa. The estimated pressure condition of ~1.3 GPa coincides well with the low-velocity anomaly observed in the mantle at ~40 km depth beneath the volcano. By comparing the results from Akita-Komagatake to the published results of the frontal-arc Iwate volcano (H = ~90 km) and the rear-arc Sannome-gata volcano (H = ~150 km), which are arranged along a cross-arc line in the Northeast Japan arc, we found that the pressure conditions of the magma generation are ~1.3 GPa at both Iwate and Akita-Komagatake, which are significantly lower than the ~1.8 GPa at the rear-arc Sannome-gata volcano. The source mantle temperature of ~1275 °C at ~1.3 GPa beneath Akita-Komagatake is higher than the ~1250 °C at ~1.3 GPa beneath Iwate, which suggests that the ascending flow of the mantle wedge corner flow may reach the shallowest levels beneath Akita-Komagatake. It was also demonstrated that the depth at which fluid was released from the subducting slab tends to increase for the volcanoes with increasing H.
  • Shouta M.M. Nakayama, Hokuto Nakata, Yoshinori Ikenaka, John Yabe, Balazs Oroszlany, Yared B. Yohannes, Nesta Bortey-Sam, Kaampwe Muzandu, Kennedy Choongo, Takeshi Kuritani, Mitsuhiro Nakagawa, Mayumi Ishizuka
    Environmental Pollution 252 1267 - 1276 2019年09月 [査読有り][通常論文]
     
    © 2019 Elsevier Ltd Metal pollution has been associated with anthropogenic activities, such as effluents and emissions from mines. Soil could be exposure route of wild rats to metals, especially in mining areas. The aim of this study was to verify whether soil exposure under environmentally relevant circumstances results in metal accumulation and epigenetic modifications. Wistar rats were divided to three groups: 1) control without soil exposure, 2) low-metal exposure group exposed to soil containing low metal levels (Pb: 75 mg/kg; Cd: 0.4), and 3) high-metal exposure group exposed to soil (Pb: 3750; Cd: 6). After 1 year of exposure, the metal levels, Pb isotopic values, and molecular indicators were measured. Rats in the high-group showed significantly greater concentrations of Pb and Cd in tissues. Higher accumulation factors (tissue/soil) of Cd than Pb were observed in the liver, kidney, brain, and lung, while the factor of Pb was higher in the tibia. The obtained results of metal accumulation ratios (lung/liver) and stable Pb isotope ratios in the tissues indicated that the respiratory exposure would account for an important share of metal absorption into the body. Genome-wide methylation status and DNA methyltransferase (Dnmt 3a/3b) mRNA expressions in testis were higher in the high-group, suggesting that exposure to soil caused metal accumulation and epigenetic alterations in rats. Soil exposure caused metal accumulation and DNA hypermethylation in rats.
  • Xiao Yan Gu, Piao Yi Wang, Takeshi Kuritani, Eero Hanski, Qun Ke Xia, Qin Yan Wang
    Earth and Planetary Science Letters 515 221 - 230 2019年06月01日 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. Large igneous provinces (LIPs) are generally considered to be related to mantle plumes and to have a great importance to the supercontinent break-up events, climate change and biological evolution over Earth's history. The high melt production rates of LIPs can be achieved under rigorous melting conditions: an abnormally high temperature, substantial decompression, addition of fusible components, or remarkable enrichment in water. Although it has been repeatedly noticed that water enrichment has occurred in many Phanerozoic LIPs, the significance of water enrichment in the mantle source for the generation of LIPs has not been explicitly highlighted. The southeastern Asian basalt province (SABP), which is thought to have formed by the Hainan mantle plume from a pyroxenite-bearing source, was emplaced over a small area of about 0.037 Mkm 2 over a long period of time from 28.5 Ma to Holocene, thus differing from a typical LIP (>0.1 Mkm 3 in volume emplaced in one or multiple pulses of less than 5 Ma). In this work, we measured H 2 O contents of high-Mg# clinopyroxene phenocrysts (12–179 ppm H 2 O) from Cenozoic basalts in the northern Hainan Island, which is part of the SABP. These data were utilized to estimate the water content of the mantle source of these basalts, yielding values in the range of 84–360 ppm H 2 O, which are significantly lower than those obtained for many Phanerozoic LIPs (thousands of ppm). After calculating the mantle potential temperature for the Hainan basalts about 170 °C higher than that for the MORB source mantle, we consider that the paucity of source water likely depressed the melt productivity and the velocity of plume upwelling, and induced the Hainan plume to stall at depths of 350–500 km, inhibiting the formation of a LIP by the Hainan plume, despite the occurrence of other favorable conditions. Hence, our results from the SABP provide evidence for the significance of water enrichment in the mantle source in the formation of LIPs. The low water content in the Hainan plume can be attributed to the incorporation of subducted slabs that had experienced significant dehydration.
  • Parham Ahmadi, Mohammad Reza Ghorbani, Massimo Coltorti, Takeshi Kuritani, Yue Cai, Anna Maria Fioretti, Eleonora Braschi, Pier Paolo Giacomoni, Farzaneh Aghabazaz, Shahrouz Babazadeh, Sandro Conticelli, Sandro Conticelli
    International Geology Review 61 2 150 - 174 2019年01月22日 [査読有り][通常論文]
     
    © 2017 Informa UK Limited, trading as Taylor & Francis Group Tertiary volcanic rocks in northwestern Firoozeh, Iran (the Meshkan triangular structural unit), constitute vast outcrops (up to 250 km2) of high-Mg basaltic andesites to dacites that are associated with high-Nb hawaiites and mugearites. Whole-rock40Ar/39Ar ages show a restricted range of 24.1 ± 0.4–22.9 ± 0.5 Ma for the volcanic rocks. The initial ratios of87Sr/86Sr and143Nd/144Nd vary from 0.703800 to 0.704256 and 0.512681 to 0.512877, respectively, in the high-Mg basaltic andesites–dacites. High-Th contents (up to 11 ppm) and Sr/Y values (27–100) and the isotopic composition of the subalkaline high-Mg basaltic andesites–dacites indicate derivation from a mantle modified by slab and sediment partial melts. Evidence such as reverse zoning and resorbed textures and high Ni and Cr contents in the evolved samples indicate that magma mixing with mafic melts and concurrent fractional crystallization lead to the compositional evolution of this series. The high-Nb hawaiites and mugearites, by contrast, have a sodic alkaline affinity and are silica undersaturated; they are also enriched in Nb (up to 47 ppm) and a wide range of incompatible trace elements, including LILE, LREE, and HFSE. Geochemistry and Sr–Nd isotopic compositions of the high-Nb hawaiites and mugearites suggest derivation from a mantle source affected by lower degrees of slab melts. Post-orogenic slab break-off is suggested to have prompted the asthenospheric upwelling that triggered partial melting in mantle metasomatized by slab-derived melts.
  • Takeshi Kuritani
    Frontiers in Earth Science 6 178  2018年11月13日 [査読有り][通常論文]
     
    © 2018 Kuritani, Yamaguchi, Fukumitsu, Nakagawa, Matsumoto and Yokoyama. The Izu-Oshima volcano is one of the most active volcanoes in Japan, and has generated relatively large-scale eruptions every 30–40 years for the past 200 years. As more than 30 years have passed since the last eruptions in 1986–87, volcanic activity is expected to resume in the near future. To help elucidate the current and future state of the volcano’s magma system, the temporal evolution of the recent magma plumbing system was investigated through a petrological and geochemical analysis of its basaltic lavas and pyroclastics (<∼53 wt.% of SiO2) that were erupted during the last ∼1.5 kyr. The basaltic products have variable phenocryst contents, ranging from ∼0 to ∼20 vol.%, and phenocryst-bearing samples commonly contain plagioclase, orthopyroxene, and clinopyroxene phenocrysts. The whole-rock compositions are significantly scattered in the Harker variation diagrams, suggesting that the compositional diversity was established by at least two independent magmatic processes. The application of principal component analysis on the whole-rock major element data suggests that one magmatic process was crystal fractionation of crystal-poor magmas, and the other process was either plagioclase accumulation or mixing of plagioclase-rich magmas. Based on this observation, and combined with the petrological analysis and previous geophysical studies, we propose that aphyric magmas, stored in an 8–10 km-deep magma chamber, progressively differentiated over time from the 7th to 20th century. Furthermore, the compositional variations in basalts resulted from the mixing of the differentiating aphyric magmas with variable proportions of porphyritic magmas derived from a 13–18 km-deep magma chamber. Because recent eruptions have been triggered by the ascent of porphyritic magma from the 13–18 km-deep magma chamber, and its injection into the 8–10 km-deep magma chamber, it is important to monitor the deeper magma chamber to predict future volcanic activity.
  • Y. Yanagida, M. Nakamura, A. Yasuda, T. Kuritani, M. Nakagawa, T. Yoshida
    Geochemistry, Geophysics, Geosystems 19 3 838 - 864 2018年03月 [査読有り][通常論文]
     
    © 2018. American Geophysical Union. All Rights Reserved. The Ichinomegata maar, located in the back-arc side of the northeastern Japan arc, erupted calc-alkaline andesitic magma with abundant deep-crustal and mantle xenoliths at about 60–80 ka. We investigated the relationship between fractionated solids and differentiated silicic melts at middle to lower crust conditions through petrologic analyses of hornblende-bearing cumulate xenoliths and melt inclusions. The Sr and Nd isotope compositions are similar to those of the host magmas, suggesting their cognate origin. The crystallization sequence is determined to be olivine, spinel → clinopyroxene → hornblende, magnetite → plagioclase → apatite, based on the observation of texture and solid solution compositions. Of the five types of xenolith studied, the leuco-hornblende gabbro preserved interstitial glass and melt inclusions with a silica content (SiO2) of 63.9–74.0 wt % and high water content (up to 8.1 wt %). Hornblende geobarometry indicates an equilibrium pressure of 0.39–0.64 GPa, which corresponds to a depth of 15–24 km. The delay of plagioclase crystallization due to high water content characterizes differentiation of the hydrous arc magma. We successfully constructed an internally consistent differentiation model of the corundum-normative calc-alkaline trend to the silicic melt inclusions, starting from primitive basalt via successive fractionation of a calculated wherlite and cumulate xenoliths. In middle to late stage differentiation, hornblende gabbros are the dominantly fractionated assemblages. Our results are consistent with published differentiation experiments of hydrous arc magmas and the lithology of the deep crust beneath the back arc of the NE Japan arc as estimated from seismic tomography.
  • Liu Jia, Xia Qun-Ke, Kuritani Takeshi, Hanski Eero, Yu Hao-Ran
    NATURE COMMUNICATIONS 8 1 2017年12月01日 [査読有り][通常論文]
     
    © 2017 The Author(s). The genesis of large igneous provinces (LIP) is controlled by multiple factors including anomalous mantle temperatures, the presence of fusible fertile components and volatiles in the mantle source, and the extent of decompression. The lack of a comprehensive examination of all these factors in one specific LIP makes the mantle plume model debatable. Here, we report estimates of the water content in picrites from the Emeishan LIP in southwestern China. Although these picrites display an island arc-like H2O content (up to 3.4 by weight percent), the trace element characteristics do not support a subduction zone setting but point to a hydrous reservoir in the deep mantle. Combining with previous studies, we propose that hydrous and hot plumes occasionally appeared in the Phanerozoic era to produce continental LIPs (e.g., Tarim, Siberian Trap, Karoo). The wide sampling of hydrous reservoirs in the deep mantle by mantle plumes thus indicates that the Earth's interior is largely hydrated.
  • Kuritani Takeshi, Sakuyama Tetsuya, Kamada Natsumi, Yokoyama Tetsuya, Nakagawa Mitsuhiro
    LITHOS 282-283 98 - 110 2017年06月01日 [査読有り][通常論文]
     
    © 2017 Elsevier B.V. The Pacific Plate subducting from the Japan Trench has accumulated in the mantle transition zone beneath NE Asia, and intraplate magmatism has been active above the stagnant Pacific slab. To understand the origin of the intraplate magmatism in relation to slab stagnation, a petrological and geochemical study was carried out on basaltic samples from a monogenetic volcano of the Fukue Volcano Group, southwest Japan. The eruption products consist of low-Si and high-Si groups, and the two magmas are hypothesized to originate from different mantle source material based on radiogenic isotopic compositions. The H2O contents of the primary magmas were estimated as ~ 2 wt.% for both the low-Si and high-Si groups. Analyses using multicomponent thermodynamics suggested that the low-Si and high-Si primary magmas were generated at ~ 2.5 GPa and 1345 °C and at ~ 1.8 GPa and 1285 °C, respectively. These results, and the geochemical characteristics of the products, indicated that the low-Si magma was generated in the asthenospheric mantle whereas the high-Si magma was produced by interaction of the low-Si magma with the sub-continental lithospheric mantle. The low mantle potential temperature of ~ 1300 °C and hydrous nature (H2O/Ce = ~ 650) of the low-Si magma suggested that the magma was generated by fluid-fluxed melting of the asthenospheric mantle. Based on these results and those obtained in previous studies, intraplate magmatism over the stagnant Pacific slab can be summarized as having been caused by either melting of the asthenospheric mantle through an influx of fluids derived from the mantle transition zone or decompression melting of a hydrous mantle plume derived from the mantle transition zone. We infer that the fluids for the flux melting have been released from the mantle transition zone where water was locally saturated. Meanwhile, hydrous mantle plumes have been generated at the mantle transition zone where a return flow of sub-lithospheric mantle material entrained beneath the subducting Pacific slab has intruded from below.
  • Bergal-Kuvikas Olga, Nakagawa Mitsuhiro, Kuritani Takeshi, Muravyev Yaroslav, Malik Nataliya, Klimenko Elena, Amma-Miyasaka Mizuho, Matsumoto Akiko, Shimada Shunjiro
    CONTRIBUTIONS TO MINERALOGY AND PETROLOGY 172 5 2017年05月01日 [査読有り][通常論文]
     
    © 2017, Springer-Verlag Berlin Heidelberg. To understand the generation and evolution of mafic magmas from Klyuchevskoy volcano in the Kamchatka arc, which is one of the most active arc volcanoes on Earth, a petrological and geochemical study was carried out on time-series samples from the volcano. The eruptive products show significant variations in their whole-rock compositions (52.0–55.5 wt.% SiO2), and they have been divided into high-Mg basalts and high-Al andesites. In the high-Mg basalts, lower-K and higher-K primitive samples (>9 wt.% MgO) are present, and their petrological features indicate that they may represent primary or near-primary magmas. Slab-derived fluids that induced generation of the lower-K basaltic magmas were less enriched in melt component than those associated with the higher-K basaltic magmas, and the fluids are likely to have been released from the subducting slab at shallower levels for the lower-K basaltic magmas than for higher-K basaltic magmas. Analyses using multicomponent thermodynamics indicates that the lower-K primary magma was generated by ~13% melting of a source mantle with ~0.7 wt.% H2O at 1245–1260 °C and ~1.9 GPa. During most of the evolution of the volcano, the lower-K basaltic magmas were dominant; the higher-K primitive magma first appeared in AD 1932. In AD 1937–1938, both the lower-K and higher-K primitive magmas erupted, which implies that the two types of primary magmas were present simultaneously and independently beneath the volcano. The higher-K basaltic magmas evolved progressively into high-Al andesite magmas in a magma chamber in the middle crust from AD 1932 to ~AD 1960. Since then, relatively primitive magma has been injected continuously into the magma chamber, which has resulted in the systematic increase of the MgO contents of erupted materials with ages from ~AD 1960 to present.
  • Kuritani Takeshi, Nakagawa Mitsuhiro
    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 17 10 4032 - 4050 2016年10月01日 [査読有り][通常論文]
     
    © 2016. American Geophysical Union. All Rights Reserved. The Rishiri Volcano is located at the very rear of the Kuril Arc at its junction with the NE Japan Arc, and its 300 km depth to the slab surface is one of the deepest among the active arc volcanoes in the world. In this study, the origin of this ultra rear-arc magmatism was investigated by analyzing the basaltic lavas from the volcano. The lavas consist of low-K and high-K groups, with the low-K lavas predating the high-K lavas. Since it is unlikely that the high-K magmas are derivatives of the low-K magmas, the two magmas are thought to be derived from different source mantle materials. Analyses using multicomponent thermodynamics suggest that these magmas were both generated through the ∼2% melting of a source mantle with 0.04–0.11 wt.% H2O at 1280–1340°C and ∼2.3 GPa. The temperatures at the surface of the subducting Pacific slab, from which the slab fluids were released, were estimated to be 860–960°C for the low-K magmas and 930–1040°C for the high-K magmas. These temperatures of the slab surface are remarkably higher than those predicted by thermal models. The estimated high temperatures of the slab surface and the latest detailed seismic tomography results suggest that the low-K and high-K magmatism resulted from the progressive production of fluids at the slab surface due to heating by the injection of hot mantle materials into a relatively large-scale fracture in the distorted portion of the subducting Pacific plate.
  • Kuritani Takeshi, Tanaka Mayumi, Yokoyama Tetsuya, Nakagawa Mitsuhiro, Matsumoto Akiko
    JOURNAL OF PETROLOGY 57 6 1223 - 1240 2016年06月01日 [査読有り][通常論文]
     
    © The Author 2016. Published by Oxford University Press. All rights reserved. The generation and evolution of basaltic magmas at Usu volcano, located at the junction between the NE Japan arc and the Kuril arc, have been investigated. The mafic products, which form the somma edifice of the volcano, consist of basalt (49.6-51.3wt % SiO2) and basaltic andesite (52.0-54.9wt % SiO2) lavas. The basaltic lavas show relatively tight compositional trends, and 87Sr/86Sr ratios tend to decrease with increasing whole-rock SiO2 content. The water content of the basaltic magmas was determined to be ~4.8wt % based on plagioclase-melt thermodynamic equilibrium. Using this information and an olivine maximum fractionation model, the water content of the primary Usu magma was estimated to be 3.9wt %. Multi-component thermodynamic calculations suggest that the primary magma was generated by ~23% melting of the source mantle with ~0.94 wt % H2O at ~1300°C and ~1.4GPa. The 0.94wt % water content of the source mantle is significantly higher than that beneath volcanoes in the main NE Japan arc (generally <0.7wt% H2O); this implies that the wedge mantle at the arc-arc junction is intensively hydrated. The temperature of the wedge mantle of ~1300°C at ~1.4GPa is also significantly higher than that of the mantle in the main NE Japan arc. Unlike the basaltic lavas, the whole-rock compositions of the basaltic andesite lavas are scattered in Harker variation diagrams. This observation suggests that the compositional diversity was produced by at least two independent processes. To elucidate the processes responsible for this compositional diversity, principal component analysis was applied to the major element compositions of the samples. This suggests that 47% of the diversity of the whole-rock compositions can be explained by mixing with partial melts of lower crustal materials, 25% is explained by redistribution of plagioclase phenocrysts, and 16% is explained by fractionation of accessory minerals.
  • Miyamoto Hideaki, Niihara Takafumi, Kuritani Takeshi, Hong Peng K, Dohm James M, Sugita Seiji
    METEORITICS & PLANETARY SCIENCE 51 5 906 - 919 2016年05月01日 [査読有り][通常論文]
     
    © 2016 The Meteoritical Society. Remote sensing observations by recent successful missions to small bodies have revealed the difficulty in classifying the materials which cover their surfaces into a conventional classification of meteorites. Although reflectance spectroscopy is a powerful tool for this purpose, it is influenced by many factors, such as space weathering, lighting conditions, and surface physical conditions (e.g., particle size and style of mixing). Thus, complementary information, such as elemental compositions, which can be obtained by X-ray fluorescence (XRF) and gamma-ray spectrometers (GRS), have been considered very important. However, classifying planetary materials solely based on elemental compositions has not been investigated extensively. In this study, we perform principal component and cluster analyses on 12 major and minor elements of the bulk compositions of 500 meteorites reported in the National Institute of Polar Research (NIPR), Japan database. Our unique approach, which includes using hierarchical cluster analysis, indicates that meteorites can be classified into about 10 groups purely by their bulk elemental compositions. We suggest that Si, Fe, Mg, Ca, and Na are the optimal set of elements, as this set has been used successfully to classify meteorites of the NIPR database with more than 94% accuracy. Principal components analysis indicates that elemental compositions of meteorites form eight clusters in the three-dimensional space of the components. The three major principal components (PC1, PC2, and PC3) are interpreted as (1) degree of differentiations of the source body (i.e., primitive versus differentiated), (2) degree of thermal effects, and (3) degree of chemical fractionation, respectively.
  • Classification of Meteorites based Purely on Bulk Elemental compositions for Analysis of Data Obtained Through Space Missions
    H. Miyamoto, T. Niihara, T. Kuritani, P.K. Hong, J.M. Dohm, S. Sugita
    Lunar and Planetary Science Conference 46. #1802 2015年 [査読有り][通常論文]
  • Asobo N E Asaah, Asobo N E Asaah, Tetsuya Yokoyama, Festus T. Aka, Tomohiro Usui, Takeshi Kuritani, Mengnjo J. Wirmvem, Hikaru Iwamori, Eric M. Fozing, Jules Tamen, Gilbert Z. Mofor, Takeshi Ohba, Gregory Tanyileke, J. V. Hell
    Chemical Geology 406 55 - 69 2015年 [査読有り][通常論文]
     
    © 2015 Elsevier B.V. Lake Nyos is located at the summit of a stratovolcano in the Oku Volcanic Group (OVG) along the Cameroon Volcanic Line. The sudden release of magmatic CO<inf>2</inf> trapped at the bottom of Lake Nyos in August 1986 caused historical casualties of 1750 people and over 3000 cattle. New geochemical data of volcanic rocks from the Nyos volcano and the first available data for volcanic rocks from other maar-bearing volcanoes (Lakes Elum, Wum and Oku) in the OVG are presented and compared. Lavas from the Nyos, Elum and Wum volcanoes show similarities in major and trace elements and Sr-Nd-Pb isotopes, suggestive of a similar mantle source. However, this source is slightly different from that of the Oku volcano. The samples from Lake Oku have lower alkali, higher TiO<inf>2</inf> and more depletion and enrichment in most incompatible trace elements than those from the Nyos, Elum and Wum volcanoes. These differences and those observed in the Sr-Nd-Pb results are consistent with a heterogeneous source for lavas in the OVG. Trace element compositions suggested the presence of garnet in the source (<6% garnet) and modelled melting results indicate <2% partial melting of the source material. Isotope data plot within the focal zone, extending towards enriched mantle 1 (EM1; e.g. Lakes Oku and Nyos samples). This indicates the involvement of at least three mantle components: depleted mid-ocean ridge basalt mantle, high-μ and EM1 components in the magmatism of the lavas studied. The contributions of these components in different proportions, originating from asthenospheric and subcontinental lithospheric mantle sources, can account for the observed variations in geochemical characteristics. The geochemical characteristics of the studied lavas indicate that the magma source need not necessarily have an abnormal CO<inf>2</inf> concentration to pose a potential threat. Degassing of an ordinary magma chamber and the migration of gas to the bottom of the lakes through cracks and faults can lead to the accumulation of CO<inf>2</inf> in lake bottoms. This is controlled by tectonic parameters (fractures and faults) that enhance degassing from the magma chamber to the lake bottom and physical parameters of the lake (e.g. size, depth, temperature and solubility) that control CO<inf>2</inf> stability.
  • Takeshi Kuritani, Takeyoshi Yoshida, Jun-Ichi Kimura, Toshiro Takahashi, Yuka Hirahara, Takashi Miyazaki, Ryoko Senda, Qing Chang, Yoshinori Ito
    CONTRIBUTIONS TO MINERALOGY AND PETROLOGY 167 2 1 - 18 2014年02月 [査読有り][通常論文]
     
    The conditions under which rear-arc magmas are generated were estimated using primary basalts from the Sannome-gata volcano, located in the rear of the NE Japan arc. Scoriae from the volcano occur with abundant crustal and mantle xenoliths, suggesting that the magma ascended rapidly from the upper mantle. The scoriae show significant variations in their whole-rock compositions (7.9-11.1 wt% MgO). High-MgO scoriae (MgO > similar to 9.5 wt%) have mostly homogeneous Sr-87/(86) Sr ratios (0.70318-0.70320), whereas low-MgO scoriae (MgO < similar to 9 wt%) have higher Sr-87/(86) Sr ratios (>0.70327); ratios tend to increase with decreasing MgO content. The high-MgO scoriae are aphyric, containing similar to 5 vol% olivine microphenocrysts with Mg# [100 x Mg/(Mg + Fe2+)] of up to 90. In contrast, the low-MgO scoriae have crustal xenocrysts of plagioclase, alkali feldspar, and quartz, and the mineralogic modes correlate negatively with whole-rock MgO content. On the basis of these observations, it is inferred that the high-MgO scoriae represent primary or near-primary melts, while the low-MgO scoriae underwent considerable interaction with the crust. Using thermodynamic analysis of the observed petrological features of the high-MgO scoriae, the eruption temperature of the magmas was constrained to 1,160-1,220 degrees C. Given that the source mantle was depleted MORB-source mantle, the primary magma was plausibly generated by similar to 7 % melting of a garnet-bearing spinel peridotite; taking this into consideration, and considering the constraints of multi-component thermodynamics, we estimated that the primary Sannomegata magma was generated in the source mantle with 0.5-0.6 wt% H2O at 1,220-1,230 degrees C and at similar to 1.8 GPa, and that the H2O content of the primary magma was 6-7 wt%. The rear-arc Sannome-gata magma was generated by a lower degree of melting of the mantle at greater depths and lower temperatures than the frontal-arc magma from the Iwate volcano, which was also estimated to be generated by similar to 15 % melting of the source mantle with 0.6-0.7 wt% H2O at similar to 1,250 degrees C and at similar to 1.3 GPa.
  • Takeshi Kuritani, Takeyoshi Yoshida, Jun Ichi Kimura, Yuka Hirahara, Toshiro Takahashi
    Mineralogy and Petrology 108 1 1 - 11 2014年 [査読有り][通常論文]
     
    The water content of low-K tholeiitic basalt magma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi-component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with variable compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4-5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived from a primary magma solely by olivine fractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mechanisms of low-K frontal-arc basalt magmas were also examined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at >~200 MPa. © 2013 Springer-Verlag Wien.
  • Takeshi Kuritani, Jun-Ichi Kimura, Eiji Ohtani, Hideaki Miyamoto, Katsuhiko Furuyama
    LITHOS 156 1 - 12 2013年01月 [査読有り][通常論文]
     
    The origin of historic potassic basalts (from the 1719 to 1721 AD eruption) from the Wudalianchi volcanic field, northeast China, is investigated. The samples examined in this study are aphyric, and contain similar to 5 vol.% olivine microphenocrysts. Geochemical analyses of the samples, along with published data for material from the 1719 to 1721 AD eruption, show that the basalts exhibit linear compositional trends in whole-rock variation diagrams, and are characterized by K2O enrichment (>4 wt.%) and an EM1-like isotopic signature. Using thermodynamic calculations and the observed petrological features of the basalts, the temperature of the magmas shortly before eruption is estimated to have been similar to 1250 degrees C, and the water content of the magma at depth is estimated to have been >similar to 1.1 wt.%. Because the estimated temperatures are significantly higher than the projected maximum temperature of the lithospheric mantle beneath the Wudalianchi volcanic field, the magmas were likely derived from the asthenospheric mantle. We suggest that both the potassic- and EM1-like natures of the basalts originated from the mantle transition zone, metasomatized by K-rich sediment fluids similar to 1.5 Ga ago through a stagnation of an ancient slab. The linear whole-rock compositional trends of the basalts primarily reflect the geochemical heterogeneity in the mantle transition zone, with variable but coupled contributions of similar to 1.5 Ga sediments in the ancient stagnant slab, and recent sediments and peridotites in the stagnant Pacific slab. We infer that the Wudalianchi magmatism was caused by an upwelling of a hydrous mantle plume from the mantle transition zone, which was hydrated through the stagnation of the ancient subducted slab and the recent Pacific slab. (C) 2012 Elsevier B.V. All rights reserved.
  • Takeshi Kuritani, Eiji Ohtani, Jun-Ichi Kimura
    NATURE GEOSCIENCE 4 10 713 - 716 2011年10月 [査読有り][通常論文]
     
    The mantle transition zone, located at depths of 410-660 km between the lower and upper mantle, is an important water reservoir in the Earth's interior(1-4). However, there are regional-scale heterogeneities in the distribution of water(4,5). The zone beneath northeast China, in particular, is remarkably hydrous(4), but when and how it became hydrous remains uncertain. Here we combine analyses of the geochemistry of late Cenozoic basalts in northeast China with published geochemical analyses. We find a spatial correlation between basalt geochemistry and the distribution of a low-velocity zone in the underlying mantle that is interpreted as a plume upwelling from the mantle transition zone(6). We therefore use the basalt geochemistry to infer the composition of the mantle transition zone. The basalts have high Ba/Th and Pb-207/Pb-206 ratios, which we suggest record an ancient hydration event in the transition zone that occurred more than one billion years ago, probably as a result of dehydration of a subducted slab. We suggest that this ancient hydration event, combined with a more recent hydration event linked to dehydration of the subducted Pacific slab(7), can account for the hydrous nature of the mantle transition zone beneath China. Our results demonstrate that the mantle transition zone can remain as a stable water reservoir in Earth's interior for timescales of more than a billion years.
  • Takeshi Kuritani, Tetsuya Yokoyama, Hiroshi Kitagawa, Katsura Kobayashi, Eizo Nakamura
    GEOCHIMICA ET COSMOCHIMICA ACTA 75 2 570 - 587 2011年01月 [査読有り][通常論文]
     
    The mechanisms and the timescales of magmatic evolution were investigated for historical lavas from the Askja central volcano in the Dyngjufjoll volcanic massif, Iceland, using major and trace element and Sr, Nd, and Pb isotopic data, as well as U-238-Th-230-Ra-226 systematics. Lavas from the volcano show marked compositional variation from magnesian basalt through ferrobasalt to rhyolite. In the magnesian basalt-ferrobasalt suite (5-10 wt% MgO), consisting of lavas older than 1875 A.D., Sr-87/Sr-86 increases systematically with increasing SiO2 content; this suite is suggested to have evolved in a magma chamber located at similar to 600 MPa through assimilation and fractional crystallization. On the other hand, in the ferrobasalt-rhyolite suite (1-5 wt% MgO), including 1875 A.D. basalt and rhyolite and 20th century lavas, Sr-87/Sr-86 tends to decrease slightly with increasing SiO2 content. It is suggested that a relatively large magma chamber occupied by ferrobasalt magma was present at similar to 100 MPa beneath the Oskjuvatn caldera, and that icelandite and rhyolite magmas were produced by extraction of the less and more evolved interstitial melt, respectively, from the mushy boundary layer along the margin of the ferrobasalt magma chamber, followed by accumulation of the melt to form separate magma bodies. Ferrobasalt and icelandite lavas in the ferrobasalt-rhyolite suite have a significant radioactive disequilibrium in terms of (Ra-226/Th-230), and its systematic decrease with magmatic evolution is considered to reflect aging, along with assimilation and fractional crystallization processes. Using a mass-balance model in which simultaneous fractional crystallization, crustal assimilation, and radioactive decay are taken into account, the timescale for the generation of icelandite magma from ferrobasalt was constrained to be <similar to 3 kyr which is largely dependent on Ra crystal-melt partition coefficients we used. (C) 2010 Elsevier Ltd. All rights reserved.
  • Takeshi Kuritani, Takeyoshi Yoshida, Yoshitaka Nagahashi
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 195 1 57 - 68 2010年08月 [査読有り][通常論文]
     
    Internal differentiation processes in a solidifying lava flow were investigated for the Kutsugata lava flow from Rishiri Volcano in northern Japan. In a representative 6-m thick lava flow that was investigated in detail in this study, segregation products darker than the host lavas manifested mainly in the form of pipes (vesicle cylinders) and layers (vesicle sheets), occurring around 0.5-23 m and 2.0-4.0 m above the base, respectively. Both the cylinders and sheets are significantly richer in incompatible elements such as TiO(2) and K(2)O than the host lavas, which suggest that these products essentially represent residual melt produced during solidification of the lava flow. Field observation and the geochemical features of the lavas suggest that the vesicle cylinders grew upward from near the base of the flow by continuous feeding of residual melt from the neighboring host lavas to the heads of the cylinders. On the other hand, the vesicle sheets were produced in situ in the solidifying lava flow as fracture veins caused by horizontal compression. The vesicle cylinders have a remarkably higher MgO content (up to 8 wt.%) than the host lava (<6 wt.%), whereas the vesicle sheets display MgO depletion (as low as 3.5 wt.%). The relatively high MgO content of the vesicle cylinders cannot be explained solely by the mechanical mixing of olivine phenocrysts with the residual melt. It is suggested that the vesicle cylinders were produced by the extraction of olivine-bearing interstitial melt from an augite-plagioclase network in the host lava, whereas the vesicle sheets were formed by the migration of the residual melt from a crystal network consisting of plagioclase, augite, and olivine in the host lava into platy fractures. We infer that this selective crystal fractionation for forming the vesicle cylinders resulted from processes in which abundant vesicles rejected from the upward-migrating floor solidification front prevented olivine crystals from being incorporated into the crystal network in the host lava. The vesicle cylinders are considered to have formed in similar to 1 day after the lava flow came to rest, while relatively large vesicle sheets (>1 cm thick) appeared much later (after similar to 9 days). The formation of these segregation products was essentially complete within 20 days after the lava emplacement. (C) 2010 Elsevier B.V. All rights reserved.
  • Takeshi Kuritani, Jun-Ichi Kimura, Tsuyoshi Miyamoto, Haiquan Wei, Taketo Shimano, Fukashi Maeno, Xu Jin, Hiromitsu Taniguchi
    LITHOS 112 3-4 247 - 258 2009年10月 [査読有り][通常論文]
     
    The mechanisms of continental intraplate magmatism were investigated with respect to Cenozoic basaltic shield lavas from the Changbaishan area, northeast China, using a comprehensive data set of major and trace elements, Sr, Nd, and Pb isotopic compositions, and K-Ar ages. The shield lavas show a significant variation in TiO(2) content (1-4 wt%), which exhibits a positive covariance with K(2)O and a negative covariance with SiO(2) for most samples. The compositional variation of the lavas cannot be explained solely by magma chamber processes, such as fractional crystallization and crustal assimilation, and may in part be attributed to processes in the magmatic source region. The variation in TiO(2) is considered to mainly reflect variations in the degree of partial melting of the source mantle, and the negative covariance of SiO(2) and TiO(2) suggests that lower-degree melts were produced at greater depths. On the basis of the observed negative covariance of TiO(2) with K-Ar ages in the main lavas, it would appear that magmas segregated at progressively greater depths with time, since at least 4.2 Ma. This feature cannot be explained in terms of temporal changes in the mantle potential temperature and/or bulk source composition. Instead, it appears likely that the rate of asthenosphere upwelling beneath the Changbaishan area decreased with time, whereby the melting depth gradually increased, resulting from a reduction in the heat flux from the upwelling mantle to the overlying lithosphere. The inferred deceleration of the asthenospheric mantle is considered to have been related to a change from an extensional to compressive tectonic stress regime during the late Pliocene. Our study suggests that long-term volcanic activity in the Changbaishan area will continue to decrease unless there is an increase in the upwelling rate of the asthenospheric mantle. (C) 2009 Elsevier B.V. All rights reserved.
  • Takeshi Kuritani
    LITHOS 110 1-4 247 - 261 2009年06月 [査読有り][通常論文]
     
    In a cooling magma chamber, magmatic differentiation can proceed both by fractionation of crystals from the main molten part of the magma body (homogeneous fractionation) and by mixing of the main magma with fractionated melt derived from low-temperature mush zones (boundary layer fractionation). In this study, the relative roles of boundary layer fractionation and homogeneous fractionation in basaltic magma bodies were examined using a thermodynamics-based mass balance model. Model calculations show that boundary layer fractionation cannot be a dominant fractionation mechanism when magma chambers are located at low pressures (<similar to 50 MPa) or when magmas are less hydrous (<similar to 1 wt.%), such as mid-ocean ridge basalt and intraplate basalt, because of the low efficiency of melt transport from the mush zones to the main magma. Therefore, magmas evolve principally by homogeneous fractionation. If crystal-melt separation does not occur effectively in the main magma, the magma becomes crystal-rich in the early stages of magmatic evolution. On the other hand, boundary layer fractionation can occur effectively when magmas are hydrous (>similar to 2 wt.%), such as arc basalt, and the magma chambers are located at depth (>similar to 100 MPa). Because the melt derived from mush zones is enriched in alkalis and H(2)O, crystallization from the main magma is suppressed by mixing with the mush melt as a consequence of depression of the liquidus temperature. Therefore, homogeneous fractionation is more effectively suppressed in magma chambers in which boundary layer fractionation is more active. If magmatic differentiation proceeds primarily by boundary layer fractionation, magmas can remain free of crystals for long periods during magmatic evolution. (C) 2009 Elsevier B.V. All rights reserved.
  • Sanjeewa P. K. Malaviarachchi, Akio Makishima, Masaaki Tanimoto, Takeshi Kuritani, Eizo Nakamura
    NATURE GEOSCIENCE 1 12 859 - 863 2008年12月 [査読有り][通常論文]
     
    Basalts at mid-ocean ridges are generated by partial melting of the Earth's upper mantle. As a result of this process, the upper mantle has become depleted over time in elements that are preferentially removed by melting(1-3). Although mid-ocean-ridge basalts have traditionally been thought to reflect the chemical composition of such depleted mantle(2-7), recent work has revealed the existence of domains in the upper mantle that are apparently not sampled by the basalts(8). Here we present the lead (Pb), neodymium (Nd) and hafnium (Hf) isotope compositions of peridotites from the Horoman orogenic massif in Japan, which is considered to represent the residues of melting of the upper mantle. These peridotites exhibit the lowest Pb isotope ratios reported from any known mantle material, along with high Nd and Hf isotope ratios. These data suggest that chemical depletion of the peridotites occurred around a billion years ago, and that they represent ancient mantle domains that have escaped convective stirring and homogenization. We suggest that such domains-if abundant in the mantle-may constitute a hitherto unrecognized reservoir with highly unradiogenic lead.
  • T. Kuritani, J. I. Kimura, T. Miyamoto, T. Shimano, F. Maeno, H. Wei, X. Jin, H. Taniguchi
    GEOCHIMICA ET COSMOCHIMICA ACTA 72 12 A505 - A505 2008年07月 [査読有り][通常論文]
  • Takeshi Kuritani, Tetsuya Yokoyama, Eizo Nakamura
    JOURNAL OF PETROLOGY 49 7 1319 - 1342 2008年07月 [査読有り][通常論文]
     
    Magma generation processes were investigated for alkali basalt lavas from Rishiri Volcano, located at the rear of the Kurile arc, using major and trace elements and Sr, Nd, Pb and Th isotopic data. The Numaura and the Araragiyama lava flows, investigated in this study, show a significant variation in TiO2 contents (1.0-1.4wt %) despite a limited variation in SiO2 content (48.5-50.0wt %); TiO2 contents correlate positively with Nd-143/Nd-144 and negatively with Sr-87/Sr-86, Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204. The compositional variations of the lavas cannot be explained by magma chamber processes, such as fractional crystallization, crustal assimilation and magma mixing, and they are suggested to have formed principally during magma generation. The variation of the TiO2 contents essentially reflects a variation of the degree of partial melting (from similar to 2 to similar to 3%) of the source mantle, and it is inferred that the melting degree correlated positively with amounts of slab-derived materials influxed into the melting region. The melting appears to have occurred progressively under isothermal and isobaric conditions, as slab-derived materials were continuously supplied. The geochemical variations in the lavas can be explained by mixing of depleted mid-ocean ridge basalt source mantle with slab-derived materials consisting of an altered oceanic crust component and a sediment component. The slab-derived materials are likely to have contained not only Sr, Ba, Pb and U, but also significant amounts of Nd and Th that are not highly soluble in aqueous fluids. The materials are thus suggested to have been supercritical liquids, and it is suggested that magma generation occurred at depths greater than that at which supercritical liquids were decomposed into aqueous fluid and silicate melt components. The lava samples show U-238-(230) Th disequilibrium with 10-20% of Th-230 excess; this Th-230 enrichment resulted primarily from the high-Th nature of the slab-derived materials.
  • Takeshi Kuritani, Tetsuya Yokoyama, Eizo Nakamura
    JOURNAL OF PETROLOGY 48 7 1295 - 1319 2007年07月 [査読有り][通常論文]
     
    Rates of magmatic processes in a cooling magma chamber were investigated for alkali basalt and trachytic andesite lavas erupted sequentially from Rishiri Volcano, northern Japan, by dating of these lavas using U-238-Th-230 radioactive disequilibrium and C-14 dating methods, in combination with theoretical analyses. We obtained the eruption age of the basaltic lavas to be 29.3 +/- 0.6 ka by C-14 dating of charcoals. The eruption age of the andesitic lavas was estimated to be 20.2 +/- 3.1 ka, utilizing a whole-rock isochron formed by U-Th fractionation as a result of degassing after lava emplacement. Because these two lavas represent a series of magmas produced by assimilation and fractional crystallization in the same magma chamber, the difference of the ages (i.e. similar to 9 kyr) is a timescale of magmatic evolution. The thermal and chemical evolution of the Rishiri magma chamber was modeled using mass and energy balance constraints, as well as quantitative information obtained from petrological and geochemical observations on the lavas. Using the timescale of similar to 9 kyr, the thickness of the magma chamber is estimated to have been about 1.7 km. The model calculations show that, in the early stage of the evolution, the magma cooled at a relatively high rate (>0.1 degrees C/year), and the cooling rate decreased with time. Convective heat flux from the main magma body exceeded 2W/m(2) when the magma was basaltic, and the intensity diminished exponentially with magmatic evolution. Volume flux of crustal materials to the magma chamber and rate of convective melt exchange (compositional convection) between the main magma and mush melt also decreased with time, from similar to 0.1m/year to similar to 10(-3) m/year, and from similar to 1m/year to similar to 10(-2) m/year, respectively, as the magmas evolved from basaltic to andesitic compositions. Although the mechanism of the cooling (i. e. thermal convection and/or compositional convection) of the main magma could not be constrained uniquely by the model, it is suggested that compositional convection was not effective in cooling the main magma, and the magma chamber is considered to have been cooled by thermal convection, in addition to heat conduction.
  • Akira Ishikawa, Takeshi Kuritani, Akio Makishima, Eizo Nakamura
    EARTH AND PLANETARY SCIENCE LETTERS 259 1-2 134 - 148 2007年07月 [査読有り][通常論文]
     
    We present a Sr, Nd, Hf and Pb isotope investigation of a set of garnet clinopyroxenite xenoliths from Malaita, Solomon Islands in order to constrain crustal recycling in the Pacific mantle. Geological, thermobarometric and petrochemical evidence from previous studies strongly support an origin as a series of high-pressure (> 3 GPa) melting residues of basaltic material incorporated in peridotite, which was derived from Pacific convective mantle related to the Ontong Java Plateau magmatism. The present study reveals isotopic variations in the pyroxenites that are best explained by different extents of chemical reaction with ambient peridotite in the context of a melting of composite source mantle. Isotopic compositions of bimineralic gamet clinopyroxenites affected by ambient peridotite fall within the oceanic basalt array, similar to those of Ontong Java Plateau lavas. In contrast, a quartz-gaenet clinopyroxenite, whose major element compositions remain intact, has lower Pb-206/(204) Pb-Nd-143/(144) Nd and higher (87)sr/Sr-86-Pb-207/(204) Pb ratios than most oceanic basalts. These isotopic signatures show some affinity with proposed recycled sources such as the so-called EM-1 or DUPAL types. Constraints from major and trace element characteristics of the quartz-garnet clinopyroxenite, the large extent of Hf-Nd isotopic decoupling and the good coincidence of Ph isotopes to the Stacey-Kramers curve, all indicate that pollution of southern Pacific mantle occurred by the subduction or delamination of Neoproterozoic granulitic lower crust (0.5-1 Ga). This crustal recycling could have taken place around the suture of Rodinia supercontinent, a part of which resurfaced during mantle upwelling responsible for creating the Cretaceous Ontong Java Plateau. (c) 2007 Elsevier B.V. All rights reserved.
  • T Yokoyama, T Kuritani, K Kobayashi, E Nakamura
    GEOCHIMICA ET COSMOCHIMICA ACTA 70 11 2885 - 2901 2006年06月 [査読無し][通常論文]
     
    In order to unravel magma processes and the geochemical evolution of shallow plumbing systems beneath active volcanoes, we investigated U-series disequilibria of rocks erupted over the past 500 years (1469-2000 AD) from Miyakejima volcano, Izu arc, Japan. Miyakejima volcanic rocks show U-238-Th-230-Ra-226 disequilibria with excess 238 U and Ra-226, due to the addition of slab-derived fluids to the mantle wedge. Basaltic bombs of the 2000 AD eruption have the lowest (Th-230/Th-232) ratio compared to older Miyakejima eruptives, yielding the youngest U-238-Th-230 model age of 2 kyr. This reinforces our previous model that fluid release from the slab and subsequent magma generation in the mantle wedge beneath Miyakejima occur episodically on a several-kyr timescale. In the last 500 years, Miyakejima eruptives show: (1) a vertical trend in a (Th-230/Th-232)-(U-238/Th-232) diagram and (2) a positive linear correlation in a (Ra-226/Th-230)(0)-1/Th-230 diagram, which is also observed in lavas from some of the single eruptions (e.g., 1940, 1962, and 1983 AD). The variations cannot be produced by simple fractional crystallization in a magma chamber with radioactive decay of Th-230 and Ra-226, but it is possibly produced by synchronous generation of melts in the mantle wedge with different upwelling rate or addition of multiple slab-derived fluids. A much more favorable scenario is that some basaltic magmas were intermittently supplied from deep in the mantle and injected into the crust, subsequently modifying the original magma composition and producing variations in (Th-230/Th-232) and (Ra-226/Th-230)(0) ratios via assimilation and fractional crystallization (AFC). The assimilant of the AFC process would be a volcanic edifice of previous Miyakejima magmatism. Due to the relatively short timescales involved, the interaction between the assimilant and recent Miyakejima magmatism has not been recorded by the Sr-Nd-Pb isotopic systems. In such cases, Th isotopes and (Ra-226/Th-230) ratio are excellent geochemical tracers of magmatic evolution. (c) 2006 Elsevier Inc. All rights reserved.
  • Takeshi Kuritani, Tomohiro Usui, Tetsuya Yokoyama, Eizo Nakamura
    GEOSTANDARDS AND GEOANALYTICAL RESEARCH 30 3 209 - 220 2006年 [査読有り][通常論文]
     
    A new method has been developed for the simultaneous determination of Pb abundance and Pb isotopic composition with high precision and accuracy for small test portion masses by thermal ionisation mass spectrometry. In this method, a Pb-205-Pb-204 double spike is added to samples prior to the chemical separation of Pb, and the isotopic composition of the spike-sample mixture is determined rigorously by the double spike technique using a Pb-207-Pb-204 spike. The isotopic composition and concentration of Pb in the sample are then obtained by utilising the principle of isotope dilution. Using this technique, replicate determinations of Pb from NIST SRM 981 and GSJ JP-1 (peridotite; 0.07 mu g g(-1) Pb) were performed. The measured concentration and isotopic data were identical, within uncertainty, to published data or to data that were determined independently in this study. The application of this method to U-Pb dating and the determination of the "initial" Pb isotopic composition was also tested. Lead isotopic compositions and the concentrations of Pb, Th and U were determined for a single batch of samples, through the addition of Pb-205-Pb-204, Th-230 and U-235 spikes to samples prior to chemical separation. Also in these experiments, we confirmed that this routine gives accurate data for Pb, Th and U concentrations and Pb isotopic compositions.
  • T Kuritani, E Nakamura
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 149 1-2 124 - 138 2006年01月 [査読無し][通常論文]
     
    Trachytic lavas of Rishiri Volcano, northern Japan, show a peculiar geochemical variation across lava flow units. Samples collected systematically in a vertical cross section from a lava flow unit with a thickness of about 20 in are nearly homogeneous in major element compositions. However, some trace elements, including Li, B and Cs, are considerably depleted in samples collected from the main part of the flow unit, compared to those obtained from the surface of the lava flow (clinker layer). In particular, Cs content of the main flow unit is as low as similar to 30% of the clinker layer. Br-11.B-10 ratios of samples from the main flow unit are also slightly lower than those of the clinker samples, and the isotope compositions positively correlate with boron concentrations. These geochemical variations cannot be explained by magmatic processes in magma chambers, post-eruptive weathering, or alteration process. Rather, we infer these systematics resulted from escape of these elements from the lava flow unit during post-eruptive degassing. Vapor phases in which Li, B and Cs dissolved ire suggested to have been transported through veins formed in the main flow unit as fractures due to slight,,hearing along the flow planes after lava emplacement. In the Tanetomi lava, only rocks of the clinker layer preserve original composition of magmas, although they are porous and brownish due to extensive oxidization. On the other hand, rocks of the main flow unit do not retain original magma compositions, although they are dense and grayish, and seem to tic much fresher compared to the clinkers, A similar geochemical modification of lavas can occur in other volcanic systems, especially for lavas consisting of relatively thick flow units. (c) 2005 Elsevier B.V. All rights reserved.
  • T Kuritani, H Kitagawa, E Nakamura
    JOURNAL OF PETROLOGY 46 7 1421 - 1442 2005年07月 [査読無し][通常論文]
     
    Mechanisms of fractional crystallization with simultaneous crustal assimilation (AFC) are examined for the Kutsagata and Tanetomi lavas, an alkali basalt-dacite suite erupted sequentially from Rishiri Volcano, northern Japan. The major element variations within the suite can be explained by boundary layer fractionation; that is, mixing of a magma in the main part of the magma body with a fractionated interstitial melt transported from the mushy boundary layer at the floor. Systematic variations in SiO2 correlate with variations in the Pb, Sr and Nd isotopic compositions of the lavas. The geochemical variations of the lavas are explained by a constant and relatively low ratio of assimilated mass to crystallized mass ('r value). In the magma chamber in which the Kutsogata and Tanetomi magmas evolved, a strong thermal gradient was present and it is suggested that the marginal part of the reservoir was completely solidified. The assimilant was transported by crack flow from the partially fused floor crust to the partially crystallized floor mush zone through fractures in the solidified margin, formed a ny by thermal stresses resultingfrom cooling of the solidified margin and heating of the crust. The crustal melt was then mixed with the fractionated interstitial melt in the mushy zone, and the mixed melt was further transported by compositional convection to the main magma, causing its geochemical evolution to be characteristic of AFC. ne volume flux of the assimilant from the crust to the magma chamber is suggested to have decreased progressively with time (proportional to t(-1/2)), and was about 3 x 10(-2) m/year at t = 10years and I x 10(-2) m/year at t = 100years. It has been commonly considered that the heat balance between magmas and the surrounding crust controls the coupling of assimilation and fractional crystallization processes (i.e. absolute value of r). However, it is inferred from this study that the ratio of assimilated mass to crystallized mass can be controlled by the transport Process of the assimilant from the crust to magma chambers.
  • T Kuritani
    LITHOS 74 3-4 117 - 130 2004年06月 [査読無し][通常論文]
     
    Magmatic differentiation processes in a cooling magma body were examined using a numerical model considering multicomponent thermodynamics and momentum, energy and species transport. The model accounts for melt transport induced by its density variation, resulting primarily from solid-liquid phase change. The equilibrium mineral assemblages, their mass fractions and their chemical compositions are determined by multicomponent thermodynamic models, and these parameters are linked with the calculations of velocity, pressure, temperature and species fields at each iteration and time step. For simplicity, solid phases are assumed to be stationary, and only olivine and plagioclase that are the earliest crystallization phases in common basaltic magmas are considered as fractionating phases. Application of the model to natural magmatic system shows that crystallization occurs selectively along the chilled boundaries soon after the cooling, and the magma body is separated into high-crystallinity mush zones and mostly crystal-free main magma. Because of the melt exchange between the mush zones and the main magma by compositional convection, the main magma evolves progressively in composition and the spatial chemical heterogeneity is grown with time. The melt segregated from the sidewall mush zone is accumulated below the roof mush zone, forming compositional stratification in the upper part of the main magma. On the other hand, the fractionated melt from the floor mush zone principally mixes with the overlying ambient magma in the middle and lower parts of the main magma body. This study shows that the direct treatment of nonlinear coupling among momentum, energy and species transport provides useful information of the thermal and chemical evolution of magma chambers as a function of time and space. (C) 2003 Elsevier B.V. All rights reserved.
  • T Kuritani, E Nakamura
    JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 18 12 1464 - 1470 2003年12月 [査読無し][通常論文]
     
    A new, simple, and practical method has been developed for the accurate and precise isotopic analysis of extremely small amounts of Pb (<&SIM;3 ng) by thermal ionization mass spectrometry. Two different types of double spikes, one consisting of Pb-205 and Pb-204 and another enriched in Pb-207 and Pb-204, are used to reduce "Pb-204 error" and to correct mass fractionation during mass spectrometry. Using this technique, replicate analyses of 1.5 ng of Pb from NBS981 were performed, and an external, precision of 0.02% (2σ) was attained for the Pb-208/Pb-204 ratio. Compared with results for 1.5 ng of Pb by the normal double spike method using a single Pb-207-Pb-204 double spike, the external precision for the isotopic ratios involving Pb-204 is reduced by about 60-70%, simply by addition of the Pb-205-Pb-204 double spike. The two double spikes method was also applied to isotopic analyses of natural rock samples, and we obtained an external precision of 0.06% (2σ) for Pb-208/Ph-204 in &SIM;1.5 ng of Pb separated from fresh peridotite; in which the Pb concentration is as low as. 3.2 ppb. This new technique is superior to any previous method for precise and accurate isotopic analyses of extremely small amounts of Pb, and will be a highly powerful tool in the future of earth science and environmental science.
  • T Kuritani, T Yokoyama, K Kobayashi, E Nakamura
    JOURNAL OF PETROLOGY 44 10 1895 - 1916 2003年10月 [査読無し][通常論文]
     
    Pre-emption processes are investigated for magmas erupted in 1983 from Miyake-jima volcano, which is one of the most active volcanoes in Japan. The whole-rock compositional trends of the eruptive products are principally smooth and linear. Magmas erupted from some fissures have compositions that deviate from the main linear trend. Phenocryst contents of samples displaced from the linear compositional trends are significantly lower than those of samples on the main trends. Anorthite-rich plagioclase phenocrysts, present throughout the 1983 products, are too calcic to have crystallized from the erupted magma composition, and were derived from a basaltic magma through magma mixing. Although the linear whole-rock composition trends favor simple two-component magma mixing.. this cannot explain the presence of samples that deviate from the main trend. Instead, the observed composition trends were formed by mixing of a homogeneous basaltic magma with andesitic magmas exhibiting compositional diversity. The original linear composition trends of the andesitic end-member magma were rotated and shifted to the direction of the basaltic end-member magma by magma mixing. The samples out of the main trends represent magmas with less basaltic component than those on the trend. The density and viscosity of the basaltic end-member magma were comparable with those of the andesitic end-member magmas. The basaltic magma, discharged from one magma chamber at similar to2 kbar pressure, was injected into a magma chamber at lower pressure occupied by the chemically zoned andesite magma (similar to1 kbar), and possibly as a fountain. To establish the characteristic mixing trend of the 1983 magma, the basaltic component must have been distributed systematically in the zoned andesite magma. A requirement is that the basaltic magma spread laterally and mixed with the andesite magma at various levels of ascent of the fountain in the host andesite magma. Analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1 kbar magma chamber.
  • Tetsuya Yokoyama, Katsura Kobayashi, Takeshi Kuritani, Eizo Nakamura
    Journal of Geophysical Research B: Solid Earth 108 2003年07月10日 [査読無し][通常論文]
     
    238U-230Th-226Ra systematics in lavas from Miyakejima volcano, Japan, are presented to estimate the timescale of magmatic processes beneath an island arc. Miyakejima volcano has four recent eruptive stages (Stages 1-4) starting >7000 BP. 238U-230Th-226Ra disequilibria observed in lavas with large 238U and 226Ra excesses imply metasomatism of depleted mantle by fluid-related processes. This metasomatism is also suggested by trace element and Sr-Nd-Pb isotopic systematics in the same lavas. In the equiline diagram, the trends for two magmatic stages (Stages 1 and 2) are regarded as two different isochrons with a common initial (230Th/232Th) ratio, although the trend for Stages 3 and 4 is a magma mixing line. Our model calculations show that slab-derived fluids can deliver some Th and a very rapid ascent time of the slab components in the mantle wedge (< 7 kyr) is inferred. This rapid ascent can be explained by nearly instantaneous material transport in the mantle wedge by a hydrofracture model for fluid and a channel flow model for melt. Such a timescale estimate is not increased even if melting processes that enhance 226Ra are taken into account. The age difference in the equiline diagram corresponds to the interval of individual fluid-release events (13 kyr between Stages 1 and 2, and 5 kyr between Stages 2 and 3 . Thus fluid release from the slab and subsequent magma generation occur as episodic events on a several-kiloyear timescale.
  • T Yokoyama, E Nakamura, K Kobayashi, T Kuritani
    PROCEEDINGS OF THE JAPAN ACADEMY SERIES B-PHYSICAL AND BIOLOGICAL SCIENCES 78 7 190 - 195 2002年09月 [査読無し][通常論文]
     
    We present U-238-Th-230-Ra-226 systematics in lavas from Miyakejima volcano, Izu arc, Japan, together with major element, trace element and Sr-Nd-Pb isotopic compositions, to estimate the timescale of magmatic processes beneath an island arc. U-238-Th-230-Ra-226 disequilibria observed in Miyakejima lavas with large excesses of U-238 and Ra-226 to Th-230 imply metasomatism of depleted mantle by fluid related processes. Our data reveal that fluid components released from the slab ascend rapidly through the mantle wedge (> 50 m/yr), and that individual stages of subaerial volcanism are induced by flushing of different fluid batches to the mantle wedge with a periodicity of 1-13 kyr. This indicates that arc magmatism is controlled by pulsed release of fluid from the slab occurring on such a small timescale, which might be related to the occurrence of earthquakes in the subducting slab.
  • T Kuritani, E Nakamura
    CHEMICAL GEOLOGY 186 1-2 31 - 43 2002年06月 [査読無し][通常論文]
     
    A simple technique has been developed for the precise analysis of lead isotope in natural rock samples by thermal ionization mass spectrometry (TIMS). Two-stage column chromatography, using 100 and 10 mul columns, was used to minimize the amounts of impurities in separated lead samples. This dramatically improved the reproducibility of mass fractionation during mass spectrometry using an ion emitter made of a mixture of silicic acid and phosphoric acid. This improvement made it possible to precisely determine the Pb isotopic compositions of very small sample sizes, employing "zero-time correction" for mass discrimination, without requiring a double-spike technique. Using the present method, analytical reproducibility of Pb-208/(204)pb of 0.02% and 0.06% (2sigma) was attained for 100 and 1 ng of Pb, respectively, separated from natural rock samples. Furthermore, we obtained a reproducibility of 0.06% (2sigma) for Pb-208/Pb-204 for 10 ng of Pb separated from GSJ JP-1 (peridotite), in which the Pb concentration was 0.09 ppm. The measured isotope compositions of USGS standard rocks AGV-1 and BCR-1 were comparable with the published values using the double-spike technique. These observations suggest that our simple technique is reliable in terms of both accuracy and precision for the determination of the Pb isotopic compositions of natural rock samples irrespective of rock chemistry and sample sizes from 1 to 100 ng of Pb. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Takeshi Kuritani
    Bulletin of Volcanology 62 8 533 - 548 2001年 [査読無し][通常論文]
     
    The trachytic Tanetomi lava from Rishiri Volcano, northern Japan, provides useful information concerning how a replenished mafic magma mixes with a compositionally zoned felsic magma in a magma chamber. The Tanetomi lava was erupted in the order of Lower lava 1 (LL1, 59.2-59.8 wt.% in SiO2), Lower lava 2 (LL2, 58.4-59.1 wt.%), and Upper lava (UL, 59.9-65.1 wt.%). Evidence for mixing with a mafic magma is observed only in the LL2, in which a greater amount of crystals derived from the mafic magma occurs in rocks with higher SiO2 content. The whole-rock compositional trend of the Tanetomi lavas is fairly smooth except for the LL2 lava composition, which scatter along the main composition trend. There is no reasonable composition of basaltic magma on the extrapolation of the LL2 composition trend, and the trend cannot be explained by a simple two-component magma mixing. Before the replenishment, the felsic magma was zoned in composition (58-65 wt.% in SiO2) and temperature (1030-920°C) in the magma chamber located at the pressure of ∼2 kbar. The compositional variation of the main felsic magma was produced by extraction of a fractionated interstitial melt from mush zones along the chamber walls and its subsequent mixing with the main magma (boundary layer fractionation). The LL1 magma tapped the magma chamber soon after the replenishment, before the mafic magma mixed with the overall felsic magma. Then the basalt magma mixed heterogeneously with the upper part of the felsic magma by forced convection as a fountain during injection. The mixing of the basalt magma with compositionally zoned felsic magma resulted in the characteristic composition trend of the LL2. The fraction of basaltic magma in the LL2 magma is estimated to be at most 10%. Despite such a small proportion, the basalt magma was mixed completely with the felsic magma, probably because the crystallinity of undercooled basalt magma was low enough to behave as a liquid. © Springer-Verlag 2001.
  • Takeshi Kuritani
    Journal of Geophysical Research B: Solid Earth 104 29401 - 29417 1999年12月01日 [査読無し][通常論文]
     
    Detailed investigation of an erupted magma with limited compositional diversity provides instantaneous information on incremental magma differentiation processes in a magma chamber. Kutsugata lava, a suitable target of such study, is a Quaternary alkali basalt (51.3-53.2 wt% in SiC>2) from Rishiri Volcano, northern Japan. Despite the narrow range in the whole rock compositional variation, chemical and modal compositions of mineral phases crystallized in the magma chamber vary systematically with the whole rock composition. In the North lava (51.3-51.9 wt% in SiOa) the less differentiated portion of the Kutsugata lava, most crystals which include low-Ni olivine and plagioclase were derived from the mushy boundary layer. The main part of the magma body was principally aphyric (<0.5 vol% crystals). Estimated chemical compositions of fractionated mineral phases during differentiation of the magma coincide with the observed compositions of low-Ni olivine and plagioclase crystals. This indicates that the main magma was differentiated by separation of crystals grown in the mush zone. The low-density interstitial melt is suggested to have been extracted from the floor mush zone with average crystallinity of >30 vol% by such mechanisms as compaction and compositional convection. This fractionated melt was mixed with the overlying main magma, causing differentiation of the Kutsugata magma. The average temperature of the extracted melt is 1010°C, significantly lower than 1100°C estimated for the main magma. A quantitative model of magmatic differentiation, which includes thermal and compositional evolution of a mushy boundary layer, can successfully reproduce the observed compositional trends of the North lava. Copyright 1999 by the American Geophysical Union.
  • T Kuritani
    GEOPHYSICAL RESEARCH LETTERS 26 13 2029 - 2032 1999年07月 [査読無し][通常論文]
     
    A boundary layer fractionation model for the thermal and compositional evolution of a basaltic magma chamber is presented. The model utilizes a multicomponent thermodynamic approach for relating the compositional structure with the thermal structure of a cooling magma body. The magma composition in the main magma body evolves by transportation of a fractionated interstitial melt from the mushy boundary layer. The consideration of both the thermal and compositional evolution of the magma body enables a realistic simulation of magmatic differentiation as a function of time and space. The model is used to evaluate a primary magma estimation from volcanic rock series. It is shown that the common procedure of olivine addition gives an estimation which is significantly different from the true primary composition if the magma actually differentiated by boundary layer fractionation. This can cause significant errors in estimating the conditions at which the primary magma was generated.
  • T Kuritani
    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 88 1-2 77 - 97 1999年01月 [査読無し][通常論文]
     
    Phenocrysts in volcanic rocks are commonly used to deduce crystallization processes in magma chambers. A fundamental assumption is that the phenocrysts crystallized in the magma chambers at isobaric and nearly equilibrium conditions, on the basis of their large sizes. However, this assumption is not always true as demonstrated here for a porphyritic alkali basalt (Kutsugata lava) from Rishiri Volcano, northern Japan. All phenocryst phases in the Kutsugata lava, plagioclase, olivine, and augite, have macroscopically homogeneous distribution of textures showing features characteristic of rapid growth throughout the crystals. Rarely, a core region with distinct composition is present in all phenocryst phases. Phenocrysts, excluding this core, are occasionally in direct contact with each other, forming crystal aggregates. The equilibrium liquidus temperature of plagioclase, the dominant phase (similar to 35 vol%) in the Kutsugata lava, can never exceed the estimated magmatic temperature, unless the liquidus temperature increases significantly due to vesiculation of the magma during ascent. This suggests that most phenocrysts in the Kutsugrata lava were formed by decompression of the magma during ascent in a conduit, rather than by cooling during residence in a magma reservoir. In the magma chamber before eruption, probably located at depth of more than 7 km, only cores of the phenocrysts were present and the magma was nearly aphyric (< 5 vol% crystals), though the observed rock is highly porphyritic with up to 40 vol% crystals. The Kutsugata magma is inferred to have been rich in dissolved H2O (> 4 wt.%) in the magma chamber, and liquidus temperatures of phenocryst phases were significantly suppressed. Large undercooling caused by decompression and degassing of the magma was the driving force for significant crystallization during ascent because of the increase in liquidus temperature due to vapor exsolution. Low ascent rate of the Kutsugata magma, which is suggested by pahoehoe lava morphology and no association of pyroclastics, gave sufficient time for crystallization. Furthermore, the large degree of superheating of plagioclase in the magma chamber caused plagioclase crystallization with low population density and large crystal size, which characterizes the porphyritic nature of the Kutsugata lava. Alkali basalt is likely to satisfy these conditions and similar phenomena are suggested to occur in other volcanic systems. (C) 1999 Elsevier Science B.V. All rights reserved.
  • T Kuritani
    JOURNAL OF PETROLOGY 39 9 1619 - 1640 1998年09月 [査読無し][通常論文]
     
    The evolution of basaltic magma by mushy boundary layer processes in a magma chamber is documented for an alkali basalt (Kutsugata lava) from Rishiri Volcano, northern Japan, on the basis of zoning patterns of plagioclase phenocrysts and their spatial distribution in the lava. Plagioclase phenocrysts with complex zoning patterns can be divided into four types. Type 1 is characterized by an extremely An-rich core (An(71-90)), which is commonly corroded and filled with sodic plagioclase. Type 2 has an Ab-rich core surrounded by a calcic mantle characteristic of partial dissolution. Type 3 is characterized by an Ab-rich core that is commonly surrounded by a reversely zoned slightly calcic mantle. Type 4 has an Ab-rich core without a calcic mantle. The An-rich cores of the Type 1 plagioclase are too calcic to have crystallized from a liquid represented by any whole-rock composition at the estimated temperatures of the Kutsugata magma system. The An-rich cores are inferred to have been formed in a mushy boundary layer along the wall of a magma chamber, where the magma was relatively cool and rich in water because of significant olivine fractionation and possibly because of addition of water expelled from the chilled margin and/or groundwater from the surrounding crust. The Ab-rich cores of Types 2-4 plagioclase phenocrysts are interpreted to have crystallized in the main magma body of the reservoir. The Types 2 and 3 Ab-rich cores were brought to the mushy layer by convection. The temporal and spatial variations of zoning patterns of plagioclase phenocrysts in basaltic lava flows give useful information on the evolution of mafic magma chambers.

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  • 硫黄溶岩についての研究
    2008年 -2010年
  • アイスランド・Askja火山におけるマグマの生成・進化プロセス
    2008年 -2009年
  • アイスランド・Askja火山におけるマグマの生成・進化プロセス
    2008年 -2009年
  • マグマ溜まり内の熱・物質輸送の理解に向けた固液境界層の再現実験
    2007年 -2008年
  • マグマ溜まり内の熱・物質輸送の理解に向けた固液境界層の再現実験
    2007年 -2008年
  • マグマ溜まり内の組成対流についての研究
    2006年 -2007年
  • マグマ溜まり内の組成対流についての研究
    2006年 -2007年

その他活動・業績

  • 中山 翔太, ジアンボ ゴルデン, 栗谷 豪, 中川 光弘, 水川 葉月, 石塚 真由美, ヤベ ジョン, 池中 良徳, ムザンド カアンプウェ, チョーンゴ ケネディ, 中田 北斗, 豊巻 治也, ベイエネ ヤレド, カタバ アンドリュー 日本毒性学会学術年会 45 (0) P -35 2018年08月10日 [査読無し][通常論文]
     
    <p>発表者らは、2008年よりアフリカのザンビア共和国カブウェ市における鉛汚染問題に関わる研究を進めてきた。当該の鉛・亜鉛鉱床地域では、1900年頃から鉱床活動が行われているが、低効率の精錬技術による多くの不純物を含む鉱さいの排出および不適切な廃棄により、地質中の鉛やカドミウムが環境に拡散している。我々の先行研究により、家畜(ニワトリ、ヤギ、ウシ)およびイヌ、野生ラットなどの動物における血中・臓器中の高濃度の鉛蓄積を確認した。さらに、鉱床周辺に住む子供300名の血中鉛濃度は、対象のほぼ全員が研究当時の基準値である5 µg/dLを超過する深刻な状況であることを解明した。この研究結果を受けて、特に子供における治療や地域の環境汚染レベルの低減を目的としたプロジェクト(<u>KA</u>bwe <u>M</u>ine <u>P</u>ollution <u>A</u>melioration <u>I</u>nitiative ~KAMPAI Project~)を2016年より実施している。本発表では、より広範囲のエリアにおける汚染状況の解明や、鉛の暴露経路解明を目的としたプロジェクトの一部結果を発表する。</p><p>ザンビア大学、ザンビア国保健省および所属機関における研究倫理許可を取得し、鉱床付近およびそれ以外のエリアも対象とした約500世帯(父、母、子供)の合計1250名における血液・血漿・尿および子供の糞便試料を採取した。血中鉛濃度は、オンサイトで測定可能なLeadCareⅡを用いて、現地クリニックにおいて測定し、鉛汚染の広がっている範囲の概要を掴むことができた。予想に反して、鉱床から離れた地域でも高濃度の血中鉛が検出される対象者の存在も明らかになった。今後は、血液や糞便における金属濃度および鉛安定同位体比解析により鉛の人への暴露経路を解明し、環境改善手法を検討する。さらに、100年間以上にも及ぶ長期慢性暴露により、動物や人におけるゲノム・エピゲノム修飾、腸内細菌叢コミュニティ変化などの可能性を予想している。近年では、鉛の毒性発現には閾値を設定できないとされているが、長期慢性暴露に伴う毒性発現メカニズムを解明し、効果的な予防法・治療法開発に貢献したい。</p>
  • Hideaki Miyamoto, Hideaki Miyamoto, Hideaki Miyamoto, Hideaki Miyamoto, Peng K. Hong, Takafumi Niihara, Takeshi Kuritani, Kenji Fukumizu, Kenji Fukumizu, Hideitsu Hino, Kenji Nagata, Shotaro Akaho, Shotaro Akaho, Shotaro Akaho, J. Alexis, P Rodriguez, J. Alexis, P Rodriguez, Hemmi Ryodo, Seiji Sugita, Masato Okada, Masato Okada, Masato Okada, Masato Okada Journal of Physics: Conference Series 1036 (1) 2018年06月27日 [査読有り][通常論文]
     
    © Published under licence by IOP Publishing Ltd. Asteroids have been observed both from the ground and through space missions for decades, which accumulated large amount of their observational data. These data are used to estimate the sizes, orbits, and even possible chemical compositions of asteroids. Even though the chemical composition is generally difficult to be accurately determined without a sample return or in-situ observation by a spacecraft, asteroids are classified based on their reflectance spectra, which are compared with those of meteorites, which are known to be mostly originated from asteroids. This scheme works reasonably well for some asteroid types, but others, mostly featureless ones in reflectance spectra, remained controversial due to the fact that the observational data of asteroids and measured data of meteorites are different in terms of the data coverage, precision and resolution. Our aim is to connect asteroids with meteorites based on sparse modelling in order to search for the optimal integration scheme for two different databases without relying on preliminary knowledge. For the above purpose, we develop large databases of asteroids and meteorites for easy application of sparse modelling. Through our analyses including principal component analysis, Bayesian spectral deconvolution and dimensionality reduction, we found that our data-driven approach can extract potential information without using empirical knowledge. Our methods show a new type of data handling scheme for asteroid and meteorite data, potentially having a significant contribution for future missions.
  • 中山翔太, YABE John, 池中良徳, MUZANDU Kaampwe, CHOONGO Kennedy, 中田北斗, 豊巻治也, BEYENE Yared, KATABA Andrew, ZYAMBO Golden, 栗谷豪, 中川光弘, 水川葉月, 石塚真由美 Journal of Toxicological Sciences 43 (Supplement) S226 2018年06月 [査読無し][通常論文]
  • 中山翔太, 豊巻治也, YABE John, MUZANDU Kaampwe, 中田北斗, 栗谷豪, 中川光弘, 水川葉月, 池中良徳, 石塚真由美 環境化学討論会要旨集(CD-ROM) 27th ROMBUNNO.3C‐08 2018年05月11日 [査読無し][通常論文]
  • Cluster analysis on the bulk compositions of meteorites
    H. Miyamoto, T. Niihara, T. Kuritani, P. K. Hong, S. Sugita ISME 13 117 -121 2014年 [査読無し][通常論文]
  • 栗谷 豪, 吉田 武義, 木村 純一, 高橋 俊郎, 平原 由香, 宮崎 隆, 仙田 量子, 常 青, 伊藤 嘉紀 日本火山学会講演予稿集 2013 (0) 2013年 [査読無し][通常論文]
  • Timescales of magmatic evolution in crustal magma chambers constrained from U-series radioactive disequilibria: a brief review
    Kuritani T Bulletin of the Volcanological Society of Japan 52 71 -78 2007年 [査読無し][通常論文]
  • Kuritani T Journal of Geography 116 133 -153 2007年 [査読無し][通常論文]
  • 栗谷 豪 地学雑誌 116 133 -153 2007年 [査読無し][通常論文]
  • T Kuritani, H Kitagawa, E Nakamura GEOCHIMICA ET COSMOCHIMICA ACTA 68 (11) A659 -A659 2004年06月 [査読無し][通常論文]
  • T Yokoyama, T Kuritani, K Kobayashi, E Nakamura GEOCHIMICA ET COSMOCHIMICA ACTA 68 (11) A634 -A634 2004年06月 [査読無し][通常論文]
  • T Kuritani, E Nakamura GEOCHIMICA ET COSMOCHIMICA ACTA 67 (18) A241 -A241 2003年09月 [査読無し][通常論文]
  • T Yokoyama, K Kobayashi, T Kuritani, E Nakamura JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 108 (B7) 2003年07月 [査読無し][通常論文]
     
    U-238-Th-230-Ra-226 systematics in lavas from Miyakejima volcano, Japan, are presented to estimate the timescale of magmatic processes beneath an island arc. Miyakejima volcano has four recent eruptive stages (Stages 1-4) starting >7000 BP. U-238-Th-230-Ra-226 disequilibria observed in lavas with large U-238 and Ra-226 excesses imply metasomatism of depleted mantle by fluid-related processes. This metasomatism is also suggested by trace element and Sr-Nd-Pb isotopic systematics in the same lavas. In the equiline diagram, the trends for two magmatic stages (Stages 1 and 2) are regarded as two different isochrons with a common initial (Th-230/Th-232) ratio, although the trend for Stages 3 and 4 is a magma mixing line. Our model calculations show that slab-derived fluids can deliver some Th and a very rapid ascent time of the slab components in the mantle wedge (<7 kyr) is inferred. This rapid ascent can be explained by nearly instantaneous material transport in the mantle wedge by a hydrofracture model for fluid and a channel flow model for melt. Such a timescale estimate is not increased even if melting processes that enhance Ra-226 are taken into account. The age difference in the equiline diagram corresponds to the interval of individual fluid-release events (13 kyr between Stages 1 and 2, and 5 kyr between Stages 2 and 3). Thus fluid release from the slab and subsequent magma generation occur as episodic events on a several-kiloyear timescale.
  • Comprehensive geochemical analyses of small amounts (<100mg) of extraterrestrial samples for the analytical competition related to the sample return mission MUSES-C
    Nakamura E, Makishima A, Moriguti T, Kobayashi K, Sakaguchi C, Yokoyama T, Tanaka R, Kuritani T, Takei H The Institute of Space and Astronautical Science Report SP16 49 -101 2003年 [査読無し][通常論文]
  • Comprehensive geochemical analyses of small amounts (<100mg) of extraterrestrial samples for the analytical competition related to the sample return mission MUSES-C
    Nakamura E, Makishima A, Moriguti T, Kobayashi K, Sakaguchi C, Yokoyama T, Tanaka R, Kuritani T, Takei H The Institute of Space and Astronautical Science Report SP16 49 -101 2003年 [査読無し][通常論文]
  • T Yokoyama, K Kobayashi, T Kuritani, E Nakamura GEOCHIMICA ET COSMOCHIMICA ACTA 66 (15A) A864 -A864 2002年08月 [査読無し][通常論文]

受賞

  • 2006年 日本岩石鉱物鉱床学会研究奨励賞
  • 2005年 日本火山学会研究奨励賞

共同研究・競争的資金等の研究課題

  • 巨大カルデラ形成噴火におけるマグマ蓄積プロセスの特異性の解明
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 栗谷 豪
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 栗谷 豪, 吉村 俊平, 中島 淳一
     
    東北本州弧~千島弧の代表的な活火山を対象にマグマ生成率を推定するため、火山岩の物質科学的解析と同地域の地殻~マントルを対象とした地震学的解析の融合的研究を行った。その結果、物質科学的研究では活火山下のマグマ生成深度におけるマントルの温度や流体量についての情報が蓄積され、一方で地震学的研究では東北本州弧~千島弧における広域的な地下構造や活火山下の局所的な地下構造について、より高解像度の情報が得られた。両手法を融合することにより、沈みこむ太平洋プレートから放出されたスラブ流体の経路などの推定を行うことができたが、マグマ生成率の推定については研究期間内では終了せず、今後引き続き行うこととなった。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2015年04月 -2019年03月 
    代表者 : 中川 光弘, 栗谷 豪, 吉村 俊平, 松本 亜希子
     
    カルデラを形成するような巨大噴火について、マグマ供給系の構造と生成過程、そして破局的噴火過程について時間軸を含めて検討した。対象とした事例は、屈斜路・支笏および鬼界火山におけるカルデラ形成噴火である。それぞれの事例で、大規模珪長質マグマは2種類の珪長質マグマの混合マグマからなり、その混合過程は噴火前の数十年から数百年前に起こっていることが明らかになった。そして破局的噴火では、その混合マグマにマフィックマグマが直前に貫入して噴火に至ったことが明らかになった。さらに破局的噴火は、いずれの事例でも時間間隙を挟む複数の噴火フェーズからなることが明らかになった。
  • 日本学術振興会:科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2016年04月 -2018年03月 
    代表者 : 栗谷 豪
     
    中国北東部下のマントル遷移層には停滞太平洋スラブが滞留しており、また顕著に水に富んでいることが地球物理学的観測によって明らかにされている。そこで本研究は、遷移層の含水量の時間変化(=停滞スラブの脱水フラックス)を明らかにすることを目的とし、スラブ直上の中国北東部~東シナ海に分布する60 Ma~0 Maの火山岩の解析を行った。その結果、ソースマントル含水量に有意な時間変化が見られなかったため、脱水フラックスを推定するには至らなかったが、60 Ma~0 Maにわたってマントル遷移層は水に富んでいたことなどを実証的に明らかにし、さらに停滞スラブ上の火成活動の要因を包括的に説明するモデルを提示した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 奥村 聡, 小園 誠史, 栗谷 豪
     
    珪長質火山活動の謎の一つは,流動を阻害する結晶を多量に含む高結晶度マグマによる爆発的噴火である.50vol%程度以上の結晶を含むマグマは固体的挙動を示すために爆発的噴火にはマグマ流動化が必要だが,そのメカニズムは不明であった.この問題を解決するために,本研究では高結晶度マグマの減圧発泡実験および粘性測定を行った.その結果,大きな減圧速度では気泡形成により固相同士が分離することでマグマが流動化し,逆に小さな減圧速度では脱ガスが進行し固化してしまうことが分かった.つまり,高結晶度マグマが爆発的噴火を起こすには,噴火前に大きな過剰圧を蓄積するなどして,大きな減圧率を達成する必要があることが分かった.
  • 日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2013年06月 -2018年03月 
    代表者 : 宮本 英昭, 杉田 精司, 栗谷 豪
     
    予定通り、隕石組成の世界最大のデータベースを構築し、このクラスタ解析から、本質的な元素の選別と共に、自動的にタイプ別の分類が行えることを示した。また小惑星・隕石双方のスペクトルについて、信頼度に応じて波長域を揃えリサンプリングした形でそれぞれについてデータベースを構築した。その解析の結果、互いに共通した潜在的クラスタ構造があるというデータ分析的な結果が得られ、高精度で対応関係を明らかにすることができた。成果は火星衛星探査計画(MMX)の創出につながり、シミュラント開発という思わぬ成果につながった。これははやぶさ2計画にも利用され、今後の探査計画にも重要な役割を果たすと期待される。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 栗谷 豪, 横山 哲也, 中村 美千彦
     
    中国北東部下のマントル遷移層は水に富んでおり、また同地域の火成活動が遷移層起源のマントル上昇流に起因することが地球物理学的観測によって明らかにされている。そこで本研究では、マントル遷移層の含水量を推定するため、中国北東部の火山岩を対象に岩石学的・地球化学的解析を行った。その結果、ソースマントルの含水量は350 ppm以上であると推定され、通常の上部マントルの含水量(約120 ppm)よりも有意に高いことが明らかとなった。またマントル遷移層の含水量として、予察的ではあるが0.7 wt.%との推定結果が得られた。
  • 日本学術振興会:科学研究費助成事業 若手研究(B)
    研究期間 : 2011年 -2012年 
    代表者 : 栗谷 豪
     
    停滞スラブが存在するマントル遷移層内での化学的プロセスを理解するため、停滞太平洋スラブの直上に位置する中国北東部の第四紀火山岩を対象に岩石学的・地球化学的解析を行った。その結果、同地域のマントル遷移層が現在の停滞太平洋スラブと原生代の停滞スラブの両方からの化学的影響を受けていたこと、原生代に水を固定したマントル遷移層は、10億年以上もの長い間、地球内部の水の貯蔵庫として安定に存在していたこと、などを明らかにした。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2009年 -2012年 
    代表者 : 中村 美千彦, 栗谷 豪, 安井 真也, 奥村 聡, 吉田 武義
     
    新燃岳2011年噴火を例に、噴火の爆発性の違い(サブプリニー式噴火とブルカノ式噴火・溶岩ドーム噴火)により、火道浅部でのマグマ滞留時間が異なることを石基の微細な結晶が記録していることを見出した。また、安山岩質軽石を出発物質として、火道浅部条件における、発泡組織の表面張力による形状緩和実験を行った。気泡の形状緩和・合体速度とその水蒸気圧依存性を明らかにするとともに、圧密が進行し、ガスポケットの形成を促す可能性があることがわかった。
  • 日本学術振興会:科学研究費助成事業 若手研究(B)
    研究期間 : 2008年 -2009年 
    代表者 : 栗谷 豪
     
    本研究は、マグマが熱・物質的に進化するメカニズムを定量的に理解することを目的として行われた。その結果、結晶化が進行するマグマ内において、気泡の多少がマグマの組成進化に影響を与えることを明らかにし、またマグマの組成進化のメカニズムとして、均質分化(マグマ溜まり主要部の結晶の沈降)と境界層分化(マグマ溜まり周縁部からの分化液の混入)が起きる条件を明確にした。さらに、アイスランドのAskja火山において、玄武岩質マグマの熱・組成進化の速さを明らかにした。
  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2005年 -2008年 
    代表者 : 谷口 宏充, 栗谷 豪, 宮本 毅, 長瀬 敏郎, 菅野 均志, 後藤 章夫, 中川 光弘, 奥野 充, 伴 雅雄, 前野 深, 嶋野 岳人, 板谷 徹丸, 安田 喜憲, 植木 貞人, 古畑 徹, 小嶋 芳孝, 中川 光弘, 伴 雅雄, 成澤 勝
     
    頭山およびそれを包括する蓋馬溶岩台地に関して、現地調査、衛星データー解析、採集した資料の化学分析・年代分析、国内の関連地層の調査・年代分析などの手法を用いて、白頭山10世紀巨大噴火の概要、白頭山及び蓋馬溶岩台地の火山学的な実態を明らかにしようとした。開始してから1年後に北朝鮮のミサイル問題・核開発問題などの諸問題が発生し、現地での調査や研究者との交流などの実施が徐々に困難になっていった。そのため、すでに収集していた試料の分析、衛星データーの解析及び国内での調査に研究の主力を移し、可能な限りの成果を得ようとした。その結果、近年発生している白頭山における地震多発とマグマ活動との関係、存在は知られているが分布や内容が全く未知である蓋馬溶岩台地の概要が明らかになり、更に、地下におけるマグマの成因についても一定の結論を得た。混乱状態にある白頭山10世紀噴火の年代問題をふくめ、また、北朝鮮からの論文を含め、研究成果は12編の論文として論文集にまとめられつつある。
  • 日本学術振興会:科学研究費助成事業 若手研究(B)
    研究期間 : 2005年 -2007年 
    代表者 : 栗谷 豪
     
    本研究の主目的は、地殻下のマグマ溜り内において、どのような時間スケールでマグマの熱・物質進化が進行するのかについて、定量的な理解を得ることである。その目的達成のため、昨年度まで利尻火山下マグマ溜まりにおける、玄武岩質マグマから安山岩質マグマへの進化の時間スケールを推定し、さらにモデル計算に基づいてマグマの熱進化を時間の関数として表現した。そこで今年度はまず、熱進化の理解の一般性を図るべく、モデル計算の結果の解析を行った。マグマ溜まり内において、熱対流の駆動力は、天井部の固液境界層と主要部マグマ間の熱境界層の温度差であり、その温度差は結晶の過冷却度に対応していると考えられているが、モデル計算で得られた過冷却度と固液境界層の成長速度の関係が、実験で得られているカンラン石の過冷却度と結晶成長速度の関係に比較的近いことが明らかになった。このことから、将来的には結晶の過冷却度と成長速度の関係から、マグマの熱進化をある程度予測できる可能性が示された。本年度はさらに、マグマ溜まり内における、主要部での結晶分化作用(均質分化)と固液境界層由来の分化液が主要部マグマに混入することによって引き起こされる分化作用(境界層分化)との結合作用について考察を行った。その結果、含水量が高いマグマが地下の比較的深部でマグマ溜まりを形成した場合、固液境界層から主要部マグマへのメルトの輸送(境界層分化)が活発になり、さらに主要部マグマのリキダス温度降下を引き起こして結晶化を抑えることによって均質分化を妨げ、その結果、境界層分化がさらに支配的になることが予測された。その一方で、地下の比較的浅部のマグマ溜まり内では、固液境界層から主要部マグマへのメルトの輸送が起こりにくいため、マグマは主に均質分化作用で進化することが明らかになった。
  • 地殻におけるマグマの熱物質進化モデルの構築
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2000年 -2002年 
    代表者 : 栗谷 豪
     
    本年度の当初の研究計画は、マグマ溜まり内における温度・組成構造の進化モデルの仕上げであった。マグマ溜まりの熱物質進化について、結晶の運動を無視するという条件付ながら、多成分系熱力学及び、物質・運動量・エネルギー保存を考慮した2次元モデルの構築を、今年度の前半に終えることができた。その後結晶の運動について、モデルへの組み込みに取り組んできたが、結晶の核密度についての予測が必要であったり、固相が支配的である領域での固相-液相の相対運動を支配するパラメータが未知であったりするといった壁に阻まれ、今年度中の完成には至らなかった。上記の研究と同時進行で、表面電離型質量分析計における鉛同位体比の測定法の開発及び改良を行った。測定時のマス分別効果の補正についてDouble spike法を導入した結果、従来の世界のあらゆる測定法よりも高確度・高精度で鉛同位体比が測定できるようになった。その成果については現在国際誌に投稿中である。また本年度は、昨年度に採取したアイスランドの岩石の解析も行った。解析の結果、アスキヤ火山の玄武岩は大規模なマグマ混合及び地殻物質の混染の影響を受けており、マグマの分化プロセスの情報を引き出すという当初の目的にそぐわないことが判明した。しかし鉛同位体比等のデータから、マグマ溜まり周囲の地殻物質が約2Maに形成されたものであること、またアスキヤ火山の玄武岩マグマはMORBのマグマと地下深部由来のマントルプリューム起源のマグマが噴火直前に混合していた可能性が示された。
  • 地殻におけるマグマの進化過程の定量的解明
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 1998年 -1999年 
    代表者 : 栗谷 豪

教育活動情報

主要な担当授業

  • 地球惑星科学文献講読
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
  • マグマ科学概論
    開講年度 : 2019年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : マグマ,火山,火山噴火,地球テクトニクス,火山災害
  • 地球惑星科学研究
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
  • マグマ科学特論
    開講年度 : 2019年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : マグマ,火山,火山噴火,地球テクトニクス,火山災害
  • 地質学実習
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 野外地質調査,ルートマップ,地形図
  • マグマ科学
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : マグマ,火成岩,造岩鉱物,元素,地殻,マントル,火山,相平衡
  • 地球惑星科学セミナー
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 宇宙,惑星,地震,火山,地球史,環境史,気象,海洋,陸水,岩石,鉱物,資源
  • 地球惑星科学文献講読
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 地球惑星科学,文献講読
  • 地球惑星科学研究
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 地球惑星科学,個別研究,研究発表、論文執筆
  • 地球惑星科学Ⅰ
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 固体地球,地球の構造と構成物質,地球史,変動する地球,自然災害
  • 地球惑星科学実験Ⅰ
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 地球惑星固体物質、偏光顕微鏡、岩石学、鉱物学、火成岩、堆積岩、変成岩、隕石、流体包有物
  • 地球惑星科学実験Ⅳ
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 岩石学, 火山学, 地球化学, 火山岩, マグマ,全球衛星測位システム, GEONET, 合成開口レーダー, 合成開口レーダー干渉法, データ処理

大学運営

委員歴

  • 2018年 - 現在   地質学雑誌   編集委員
  • 2017年 - 現在   岩石鉱物科学   編集委員
  • 2004年 - 現在   Island Arc誌   編集委員   Island Arc誌
  • 2012年 - 2016年   火山   編集委員


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