著者

笠原 順三 阿部 なつ江 荒井 章司 下司 信夫 熊谷 英憲 丸山 茂徳 小原 一成 小原 泰彦

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.117, no.1, pp.1-4, 2008-02-25 (Released:2010-02-10)

参考文献数

17

著者

荒井 章司 阿部 なつ江

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.117, no.1, pp.110-123, 2008-02-25 (Released:2010-02-10)

参考文献数

56

被引用文献数

9 7

---

This article reviews interpretations of the geological and petrological nature of the Moho, which is defined as a discontinuity in terms of Vp, with a view to preparing for the Mohole on the ocean floor in IODP. We strongly propose discarding non-seismic terms for the Moho, such as “petrologic Moho”. The nature of the Moho has been controversial for a long time; an isochemical phase transition boundary between gabbro (crust) and eclogite (mantle) was favored for the Moho by some researchers, while a chemical boundary between mafic rocks (crust) and peridotite rocks (upper mantle) is now favored by a majority of researchers. Boundaries between completely or partially serpentinized peridotite and fresh peridotite may be applicable as the Moho at some parts of the ocean floors of a slow-spreading ridge origin. Antigorite serpentinite can be expected to be observed at the lowermost crust if the Moho is the serpentinization front at the stability limit of serpentine. The Moho beneath the Japan arcs can be estimated using mafic-ultramafic xenoliths in Cenozoic volcanics. Peridotitic rocks scarcely mix with feldspathic rocks, indicating that the Moho at that location is the boundary between feldspathic rocks (mostly mafic granulites; crust) and spinel pyroxenites (mantle). Possible fossil Mohos are observed in well-preserved ophiolites, such as the Oman ophiolite. Two types of Moho are distinct in the Oman ophiolite; gabbro-in-dunite Moho, where a gabbro band network in dunite changes upward to the layered gabbro within a few to several tens of meters, and dunite-in-gabbro Moho, where late-intrusive dunites intruded into gabbros. The former is of a primary origin at a fast-spreading ridge, and the latter is of a secondary origin at a subduction-zone setting in the obduction of the oceanic lithosphere as an ophiolite. The gabbro/peridotite (dunite) boundary as the primary Moho forms in embryo as a wall of melt conduit at fast-spreading ridges as well as at the segment center of slow-spreading ridges. The oceanic primary Moho is modified to various degrees by magmatism, metamorphism and tectonism in subsequent arc and continental environments. The gabbro-in-dunite Moho formation in the Oman ophiolite is an embryo of this modification. We expect in-situ sampling across the primary oceanic Moho formed at a fast-spreading ridge through the Mohole of IODP. Ultra-deep drilling at gabbro/peridotite complexes exposed on the ocean floor is indispensable for our understanding of the suboceanic upper mantle. Studies on appropriate ophiolites and deep-seated xenoliths from oceanic areas should complement the Mohole and other ultra-deep drillings to grasp the whole picture of the oceanic upper mantle.

著者

荒井 章司

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.2, pp.392-410, 2010-04-25 (Released:2010-07-06)

参考文献数

87

被引用文献数

7 9

---

Various characteristics of podiform chromitites, an enigmatic mantle rock member, are reviewed in this article. Chromitites are composed of chromian spinel, with the general formula (Mg, Fe2+)(Cr, Al, Fe3+)2O4, and silicates (mainly olivine). The Fe3+ content is generally very low, being less than 0.1 to all trivalent cations, in mantle chromian spinels. The Mg/(Mg + Fe2+) ratio (= Mg#) changes inversely with the Cr/(Cr + Al) ratio (= Cr#), which increases with an increase of degree of partial melting of mantle peridotites. The Cr# of chromian spinel is generally higher than 0.4 (generally 0.6 to 0.8) in podiform chromitites, varying widely from 0.1 to 0.9 in the mantle peridotite. The podiform chromitite forms pod-like bodies (dimensions of up to 1.5 km × 150 m for an individual pod) with a dunite envelope, totally set within mantle harzburgite. In well-preserved ophiolites, they occur in the uppermost mantle, especially in and beneath the Moho transition zone, which is dominated by dunite. The Cr# of chromian spinel is relatively low (0.4 to 0.6) around the Moho transition zone, and high (>0.6) at deeper levels in the mantle section. Chromitites are denser and less anisotropic in Vp than peridotites, and the Vp is 8.5 to 9 km/sec depending on the proportion of chromian spinel, and higher in the former than in the latter.  The podiform chromitite has been interpreted to be one of melt/rock interaction products within the uppermost mantle harzburgite; hybridization of relatively Si-rich melt formed by the breakdown of orthopyroxenes of the wall harzburgite and subsequently supplied primitive melt cause oversaturation in chromian spinel, giving rise to formation of chromitite with a dunite envelope. The fractionated melt leaving high-Cr# podiform chromitite is possibly of arc-magma affinity. Chromitites with low-Cr# (0.4 to 0.6) chromian spinel can be in equilibrium with MORB. Recently found ultra-high pressure minerals, such as diamond, moissanite, Fe-silicides and Ni-Fe-Cr-C alloys, within chromian spinel of podiform chromitites make the genetical history of chromitites highly enigmatic. A new story, which incorporates the genesis and involvement of these highly reducing, ultra-high pressure minerals, is required.

著者

海野 進 仙田 量子 石塚 治 田村 明弘 草野 有紀 荒井 章司

雑誌

日本地球惑星科学連合2018年大会

巻号頁・発行日

2018-03-14

---

地球の全マントルの50–70 wt%を占める枯渇したマントルは大陸地殻を形成した融け残り岩とされている[1]。これらの枯渇したマントルは,クラトン下のリソスフェアや海底下の対流するアセノスフェアを構成するが,それらがいつ地球創生期の始原的マントル(PUM)から分化し,どのようなプロセスで形成されたかを明らかにすることはマントルの物質的進化を理解する上で重要である。 カンラン岩の溶融時にOsの親核種であるReがメルトとともに完全に融け残り岩から失われると,融け残り岩のOs同位体比はそれ以降変化しない。この仮定のもとに始源的マントル(PUM)から融け残りカンラン岩を生成したRe枯渇年代が決められる。クラトン下のリソスフェアの多くはOs同位体比(187Os/188Os)が0.11以下と低く,始生代末~原生代初めのRe枯渇年代を示すことから,その頃にPUMが大規模に融解し,対流するマントルから切り離された融け残り岩と考えられる[2, 3]。一方,中央海嶺玄武岩(MORB)のソースとなる対流するマントル(DMM)は,Os同位体比が0.116–0.135と幅広く,多くは10億年前より若いRe枯渇年代を示すことから,原生代以降の様々な時期に対流による溶融と混合・攪拌を通じて形成されたと考えられてきた。しかし,高枯渇ハルツバージャイトを主体とするクラトン下リソスフェアとは異なり,DMMの多くはPUMからメルトを3–4 wt%取り去った程度の低枯渇度で,溶融後も相当量のReが残存していたはずである。すなわちDMMは従来考えられた以上に古い時代に分化した可能性がある。 そこでRe-Osアイソクロンが適用困難な融け残りカンラン岩について,Re/Os比の初期値をメルト組成から独立に推定する方法を提案する [4]。PUMからの分化時に融け残りカンラン岩と平衡であったメルトのREE組成についてモデル計算をし,融け残り岩のYb濃度を推定することによってPUMの部分溶融度,すなわち融け残り岩のRe/Os比の初期値を決めることができる。このRe/Os比と Os同位体比をもとにOs同位体進化曲線を計算すれば,分化年代が得られる。最近,著者らは伊豆―小笠原―マリアナ(IBM)前弧域の無人岩マグマ由来のCrスピネルとメルト包有物の解析から,初生無人岩マグマのソースマントルが2種類あり,それぞれ37–32億年前と17–15億年前にPUMから分化した融け残り岩であることを明らかにした[4]。同様に,Os同位体比0.125を有する平均的なDMMは26–22億年前にPUMから分化したことがわかった。これらの3つの年代は丸山[2002]が示した大陸形成が最も活発であった時期と合致する(図1)。また,平均的なDMM分化が起きた26–22億年前はクラトン下リソスフェアのRe枯渇年代と一致する。このことから,大規模な大陸形成をもたらしたマントル対流の活動期パルスが幅広いOs同位体比を示すDMMの生成にも関与したと考えられる。[1] Zindler, A., and Hart, S., 1986. Ann. Rev. Earth Planet. Sci.,14, 493 - 571[2] 仙田量子ほか,2012. 岩石鉱物科学,41, 211 – 221[3] Walker, R. J., 2016. Geochemical Perspectives, 5[4] Umino, S. et al., 2018. Island Arc, doi: 10.1111/iar.12221[5] 丸山, 2002.プルームテクトニクスと全地球史解読, 岩波書店

著者

高橋 直樹 荒井 章司

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.89, no.3, pp.101-114, 1994-03-05 (Released:2008-03-18)

参考文献数

26

---

Large amounts of basalt gravels are associated with serpentinite gravels in the Senhata Formation of the Miura Group (uppermost Miocene) in the Boso Peninsula, central Japan. The basaltic rocks possibly constitute a presumed mafic-ultramafic complex (“Fudoiwa serpentinite mass”) in the Tokyo Bay area, which belongs to the Circum-Izu Massif Serpentine Belt. They are slightly altered and have phenocrysts of olivine±clinopyroxene±plagioclase; they are sometimes picritic. Chromian spinel is common both as euhedral inclusions in olivine and as microphenocrysts, and clinopyroxene is often titanaugite. Bulk rock chemistry indicates that intraplate alkali basalts are dominant in the Senhata basalt gravels. Relic chromian spinel chemistry also suggests that the alkali basalts and the picritic basalts are of intraplate magma origin. The close association of intraplate basalts with the Fudoiwa serpentinites may be compatible with the presence of Ti-rich wehrlitic cumulates and Ti-rich metasomatites in the Fudoiwa mass reported by Arai et al. (1990). In the Circum-Izu Massif Serpentine Belt, alkali basalts tend to be associated with small-scale serpentinite masses, and tholeiitic ones, with large-scale masses.

著者

荒井 章司 阿部 なつ江 松本 一郎 三浦 真

出版者

一般社団法人日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.55, no.1, pp.5-30, 2021-03-25 (Released:2021-03-25)

参考文献数

146

---

Chromitites (chromite ores) are reviewed for their importance in magmatism, hydrothermalism, geodynamics and production of resources. The key process for chromitite production is possibly the formation of magmas oversaturated with chromite (or chromian spinel).Production of relatively silica-rich magma during the formation of dunite envelope is coupled with the production of the podiform chromitite. The origin of stratiform chromitites is challenged based on a new idea on the origin of chromite-hosted mineral inclusions, commonly found in all types of chromitites. The chromite-hosted melt inclusions, now characterized by the assemblage pargasite+aspidolite+orthopyroxene, are possibly formed during reaction melting of orthopyroxene within the mantle. Chromite grains in the crustal stratiform chromitites, at least in part, are produced in the mantle stage and transported upward to the magma chamber. Origin of ultrahigh-pressure chromitites has been highly debated, but is still enigmatic. Chromitites of hydrothermal origin have been found and may contribute to redistribution of Cr both in the mantle and in the crust. Production of chromitite ores in Japan is also reviewed. Chromitites serve as a good petrologic marker in both mantle and crustal rocks, and will greatly contribute to our understanding of deep-seated structure and mantle processes in the mantle drilling.

著者

伊藤 久敏 山田 隆二 田村 明弘 森下 知晃 荒井 章司

出版者

The Geological Society of Japan

雑誌

日本地質学会学術大会講演要旨 (ISSN:13483935)

巻号頁・発行日

pp.143, 2012 (Released:2013-03-26)

著者

荒井 章司

出版者

静岡大学地球科学教室

雑誌

静岡大学地球科学研究報告 (ISSN:03886298)

巻号頁・発行日

no.20, pp.p175-185, 1994-03

被引用文献数

4

---

The Circum-Izu Massif Serpentine Belt is a fossil transcurrent plate boundary of the Oligocene-Miocene time beween the Philippine Sea and the Eurasia plates. The Circum-Izu Massif Serpentine Belt encircles the northern end of the Izu Massif, almost parallel to a trace of the present plate boundary, the Sagami Trough and the Suruga Trough. The Circum-Izu Massif serpentinite had been mainly emplaced into or protruded onto the Oligocene-Miocene sediments. The Circum-Izu Massif peridotite, mainly harzburgite, is characterized by the mineral assemblage, olivine (Fo_<90-92>) + opx + cpx + chromian spinel (Cr#, ca. 0.5) +/- plagioclase (An_<90>), and is a low-pressure (ca. 5 kb) restite with or without melt impregnation. It may represent the uppermost mantle of the Shikoku Basin, which had begun opening during Oligo-Miocene, protruded along the transcurrent plate boundary at the northern end of the Philippine Sea plate ( the Shikoku Basin ) , by analogy with the protrusion of abyssal peridotites along the oceanic fracture zone. It had been accreted to the Eurasia plate by the ocean-ward bending of the central Honshu arc during the opening of the Sea of Japan in the Miocene. Detrital chromian spinel grains in the Oligocene-Miocene sediments in the Circum-Izu Massif Serpentine Belt memorize some ancestral peridotites with arc-mantle characteristics which had been protruded in the Belt before the present Circum-Izu Massif serpentinite (peridotite). The ancestral peridotites and dioritic rocks frequently associated with the sepentinites were derived from the deep parts of the Paleo-Izu-Bonin arc, which had been split and disrupted by the Shikoku Basin opening. Picritic basalts of intra-plate type closely associated with the Circum-Izu Massif serpentinite were possibly derived from the mantle plume which had caused the opening..

著者

末岡 茂 田上 高広 堤 浩之 長谷部 徳子 田村 明弘 荒井 章司 山田 隆二 松田 達生 小村 健太朗

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.1, pp.84-101, 2010-02-15 (Released:2010-05-21)

参考文献数

62

被引用文献数

9 8

---

Quantitatively estimating denudation is generally difficult because it essentially involves the removal and loss of materials in situ. The denudation rate of mountainous areas in Japan has commonly been studied from the volume of sediment in a basin or catchment. Nonetheless, the availability of these methods is constrained spatially by upstream area and temporally by depositional age. In the last few decades, thermochronometric methods that evaluate thermal history using radiometric-dating methods have been used to evaluate the denudation and tectonic history of orogenic belts around the world. The advantages of thermochronometric methods are that we can calculate the denudation rate at each sampling point and that combining multiple methods and/or target minerals enables us to calculate denudation rates in multiple periods. However, thermochronometric methods have been applied to areas with extraordinarily high denudation rates in island arc areas such as Japan. Thus, the effectiveness of thermochronometric methods for estimating denudation rates in island arc areas has not been demonstrated. We applied apatite and zircon fission-track thermochronometry to granitic rock samples collected from outcrops and a borehole to estimate the tectonic history of the Rokko area, southwest Japan. Previous studies suggested that the Rokko Mountains have been uplifted by active faulting along their northern and southern margins during the Rokko movements, a Quaternary tectonic movement in the Kinki district. However, the tectonic history of the Rokko area prior to 1 Ma has not been revealed due to a lack of prevalent geologic markers. We estimated average denudation rates in various periods based on apatite and zircon FT ages and previously reported radiometric ages. We obtained denudation rates at about 0.04-0.10 mm/yr after about 30 Ma, 0.05-0.7 mm/yr during 50-30 Ma, 0.7-4.0 mm/yr during 70-50 Ma. The denudation rate after the deposition of the Kobe Group (36.9-30.4 Ma) is estimated to be in the 0.01-0.1 mm/yr order, while bedrock uplift rate after about 1 Ma is estimated to be about 0.5 mm/yr. Thus, the tectonic activity of the Rokko Mountains area prior to 1 Ma has been relatively low.

著者

佐藤 努 秋田 奈生子 大世古 光弘 荒井 章司 福士 圭介 横山 信吾

出版者

極限環境生物学会

雑誌

極限環境微生物学会誌 (ISSN:13485474)

巻号頁・発行日

vol.3, no.1, pp.1_60-1_67, 2004 (Released:2007-05-18)

参考文献数

26

著者

荒井 章司

出版者

金沢大学21世紀COEプログラム

雑誌

環日本海学:森・海・空のメッセージ

巻号頁・発行日

pp.3-11, 2006-08-01

---

金沢大学大学院自然科学研究科

著者

高橋 奈津子 荒井 章司 室田 祐一

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.95, no.4, pp.311-329_2, 1989-04-15 (Released:2008-04-11)

参考文献数

54

被引用文献数

9 6

著者

二ノ宮 淳 荒井 章司

出版者

日本鉱物科学会

雑誌

岩鉱 : 岩石鉱物鉱床学会誌 : journal of mineralogy, petrology and economic geology (ISSN:09149783)

巻号頁・発行日

vol.93, no.7, pp.235-249, 1998-07-05

参考文献数

19

被引用文献数

1 5

---

ニュージーランド,オケテのベイサナイトおよびそのかんらん岩捕獲岩とメルトの反応物中のかんらん石,スピネルを記載した。かんらん石斑晶は二種類に大別できる。斑晶 (I) (コアでFo₈₅-Fo₇₆, リムでFo₇₆) は小型で自形性が高く,非変形で,細粒スピネルを包有する。斑晶 (II) (コアはFo₉₀ 以下で均質,リムはFo₈₅-Fo₇₆ の正累帯) は大型で,自形&sim;他形である。コアは変形組織を有し,リムのみスピネルを包有する。斑晶 (I) のうち,低Fe³⁺ グループのスピネル (高Cr#) を包有するものは,かんらん岩中の斜方輝石とメルトの反応物起源,高Fe³⁺ グループのスピネル (低Cr#) を有するものは,メルトから結晶化したものであろう。斑晶 (II) は外来結晶 (かんらん岩起源) 起源で,化学的,形態的に様々な改変を受けている。ピクライト玄武岩やアルカリかんらん石玄武岩のような,かんらん石斑晶に富む火山岩中のかんらん石斑晶は,メルトとかんらん岩との反応により,多起源性たり得る。

著者

荒井 章司

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.41, no.6, pp.247-256, 2012 (Released:2012-12-29)

参考文献数

56

被引用文献数

4 4

---

Podiform chromitites have been interpreted as cumulates formed via melt/harzburgite reaction and subsequent melt mixing within the upper mantle. Recent finding of ultrahigh-pressure (UHP) minerals such as diamond from some podiform chromitites has, however, seriously required us to reconsider the whole framework of podifrom chromitite genesis. The UHP podiform chromitites are characterized by presence of frequent silicate lamellae in chromian spinel and only PGE (platinum-group elements) alloys as platinum-group minerals. The UHP chromitites were possibly formed by deep recycling of the ordinary low-pressure podiform chromitites. Diamonds could be formed by reduction of CO2 metasomatically supplied to chromian spinel in advance. Silicate lamellae in chromian spinel of UHP chromitites were possibly derived from primary silicate inclusions (pyroxenes, pargasite and Na phlogopite), commonly found in the low-pressure chromitite. They were decomposed/partially melted and resolved in high-pressure chromian spinel during compression/heating during downward transportation, and were exsolved as silicate lamellae on decompression/cooling during uprising. PGE sulfides commonly found in the low-pressure chromitite may have been decomposed to PGE alloys and sulfur-rich melt/fluid that were removed outside.   We should systematically re-examine all podiform chromitites that have been ever documented, but our preliminary examination indicates that both concordant and discordant chromitites from Oman ophiolite are of low-pressure origin, containing primary pargasite inclusions in chromian spinel. More thorough characterization of the UHP chromitite may enable us to place constraints on the style of mantle convection that provided the MORB source possibly comprising the UHP chromitite. Possible presence of ringwoodite as one of UHP minerals in chromitite may favor the two-layer mantle convection for supplying the source mantle that formed the oceanic lithosphere.

著者

宿野 浩司 荒井 章司

出版者

一般社団法人 日本鉱物科学会

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.94, no.4, pp.120-140, 1999 (Released:2006-08-07)

参考文献数

39

被引用文献数

8 8

---

西南日本,中国地方には,新生代玄武岩類が多数存在しており,それらは火山群を形成している。これらの玄武岩中のかんらん石斑晶とそれらに包有されたクロムスピネルの化学組成から,マントルレスタイトを推定した。推定されたマントルレスタイトは,各々の玄武岩火山群において特徴的な性質を示すことがわかった。すなわち,津山,吉備,世羅ではレールゾライト; 黒岩高原,横田,比婆ではレールゾライトからハルツバーガイト; 松江ではレールゾライト(11 Ma)とハルツバーガイト(1 Ma),倉吉ではハルツバーガイト; 隠岐島後ではレールゾライトである。この結果は,従来の溶融実験から求められた融け残り岩と,ほぼ一致している。また,中国地方の玄武岩中のクロムスピネルの Cr# は,時間とともに高くなる傾向がある。これらは,西南日本において度重なる玄武岩活動によって,もたらされたものであると考えられる。

著者

松本 剛 宮下 純夫 荒井 章司 森下 知晃 前田 仁一郎 熊谷 英憲 大友 幸子 Henry J.B. DICK

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.112, no.5, pp.Plate3, 2003-10-25 (Released:2009-11-12)

著者

荒井 章司 田村 明弘 三浦 真 清家 一馬

出版者

一般社団法人日本鉱物科学会

雑誌

日本鉱物科学会年会講演要旨集 日本鉱物科学会 2016年年会

巻号頁・発行日

pp.193, 2016 (Released:2020-01-15)

---

大阪市南部に新たなマントル捕獲岩産地が発見された。7.5 Maのアルカリ玄武岩岩脈中に産する。捕獲岩としてはレールゾライトのみが見出される。かんらん石の組成はFo91前後,スピネルのCr#は0.2~0.3である。フロゴパイトを含むものはややFeに富む(かんらん石,Fo91~88)。前者は海洋底のレールゾライトに似る。後者は前者がプレート内マグマにより交代作用を受けたものである。

著者

森下 知晃 荒井 章司 田村 明弘 石田 義人

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.37, no.1, pp.1-14, 2008 (Released:2008-05-12)

参考文献数

92

---

A peculiar amphibolite rich in deep vivid green-colored amphibole porphyroblast was found as a boulder in the Chiroro River of Hidaka Town, Hokkaido, Japan. The amphibolite mainly consists of deep vivid green-colored amphibole (porphyroblast), colorless amphibole (matrix) and plagioclase with a small amount of chlorite, epidote and chromian spinel. Deep vivid green-colored amphibole porphyroblast is more than 20 modal % in the rock. Chromian spinel rarely occurs as inclusions in deep vivid green-colored amphibole porphyroblast. The Cr2O3 content of the deep vivid green-colored domain is usually ∼1 wt% (up to 2.5 wt% nearby chromian spinel) whereas that of colorless amphibole in the matrix is low, < 0.1 wt%. Deep vivid green-colored amphibole porphyroblast is heterogeneous in chemical compositions within each grain and is divided into three domains as follows: (1) high-Cr2O3 (∼1 wt%, up to 2.5 wt%) and Al2O3 (> 10 wt%) green-colored domain, (2) relatively high-Cr2O3 (∼1 wt%) and low- Al2O3 (< 10 w%) green-colored domain and (3) low-Cr2O3 (< 0.1wt%) and Al2O3 (< 10 wt%) colorless domain. Chondrite-normalized rare earth element (REE) patterns of both deep vivid green-colored amphibole porphyroblast and colorless amphibole in the matrix are characterized by low light REE with positive Eu anomaly. The Cr#[= Cr/(Cr + Al) atomic ratio] and TiO2 content of chromian spinel in the amphibolite are similar to those in a serpentinite complex of the Kamuikotan Zone. The amphibolite was formed by either amphibolitization of a rock containing chromian spinel derived from the surrounding serpentinite complex or extensively metasomatized serpentinite due to interaction with surrounding metamorphic rocks.

著者

芳川 雅子 荒井 章司 柴田 知之 石丸 聡子

出版者

一般社団法人日本地球化学会

雑誌

日本地球化学会年会要旨集 2011年度日本地球化学会第58回年会講演要旨集

巻号頁・発行日

pp.374, 2011 (Released:2011-09-01)

---

スラブや堆積物由来成分によるマントルウェッジのより詳細な改変過程を明らかにするため、西南日本弧背弧域福岡県玄界島沖の黒瀬に産するマントルかんらん岩捕獲岩6試料の鉱物の主要元素組成および単斜輝石のSr-Nd同位体・微量元素組成を求めた。その結果、フラットからV型のコンドライト規格化微量元素組成パターンを示し相対的に低いNd同位体比を示すタイプ2(Yoshikawa et al., 2010)の捕獲岩が多く認められることがわかった。これらの捕獲岩試料中の単斜輝石は様々な程度の負のZr・Ti異常を示し、単斜輝石のCeN/YbN比とスピネルのCr#(100xCr/Cr+Al値)に相関がなく、さらに非常に肥沃したSr-Nd同位体組成を示すものが含まれ、起源マントルが部分溶融した後に沈み込むスラブや堆積物由来の成分による交代作用を被った可能性が高いことを示唆している。

著者

阿部 なつ江 荒井 章司

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.34, no.4, pp.143-158, 2005 (Released:2005-09-10)

参考文献数

89

被引用文献数

6 12

---

Recent developments in instrumentation for in situ trace element analysis of peridotite minerals give us valuable data set of petrological and geochemical insights of the upper mantle. Here, we summarize petrographical, petrological and geochemical characteristics of mantle xenoliths from the Northeastern and Southwestern Japan arcs. They have clear correlations between microtexture and mineral compositions in terms of both major and trace elements. That suggests that influx-assisted melt extraction occurs simultaneously with deformation/recrystalization in the upper mantle. Their characteristics of trace-elements in clinopyroxene are distinguished from those of abyssal peridotite and peridotite xenoliths from continental regions. The geochemistry of Japan arcs’ clinopyroxenes have characteristics of arc-type mantle source; i.e., low light rare earth element (LREE) and high field strength element (HFSE; Ti, Zr and so on), rather high heavy rare earth (HREE) relative to LREE elements and Sr concentrations. They also have a rather constant Ti/Zr ratio, variable REE patterns, and relatively low LREE/HREE ratios. The simple melt extraction model can not explain these characteristics. These features are due to metasomatism, which is different from carbonatite metasomatism.