著者

高木 哲一

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.88, no.4, pp.165-178, 1993-04-05 (Released:2008-03-18)

参考文献数

66

被引用文献数

5 4

---

This paper describes the petrography of magnetite-series and ilmenite-series granitoids in the San'yo and San'in belts, and estimates the redox paths of the granitoid magmas during cooling. In magnetite-series granitoids in these areas, the magnetite commonly occurs as secondary minerals after decomposition of magmatic mafic silicates such as pyroxenes, hornblende and biotite. The magnetite is divided into two types, differentiated by their coexisting minerals. The first-type of magnetite crystallizes concurrently with hornblende and biotie after decomposition of pyroxenes and brown hornblende at the late magmatic stage, and continues to crystallize during subsolidus conditions. The second-type of magnetite crystallizes with actinolite, cummingtonite and chlorite during subsolidus stages of crystallization. Petrography, combined with Fe-Ti oxide geothermo-barometers for the magnetite-series granitoids, suggests that the magnetite crystallizes due to an increase in the oxidation state of the magma (and/or fluid phase) above the NNO-buffer during cooling. However, the redox states of the ilmenite-series granitoid magmas are kept below the FMQ-buffer, throughout the solidifying process of the magma. The chemistry of the fluid phase determines whether the magma follows the magnetite-series or ilmenite-series trend.

著者

森下 知晃 小寺 忠広

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.93, no.2, pp.52-63, 1998 (Released:2006-08-30)

参考文献数

38

被引用文献数

9 12

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北海道様似郡様似町を流れるポンサヌーシベツ川よりコランダムの巨晶を含むガブロの転石を発見した。このガブロの供給源はガブロの鉱物組み合わせ,組織,化学組成の特徴から幌満かんらん岩体に産するGBIIガブロ(塩谷・新井田,1997)であると推定される。コランダムと他の鉱物との組織的な関係はコランダムがガブロ(=GBII)の最も新しい変成条件下では不安定であったことを示す。コランダムの分解反応はガブロ(=GBII)が温度上昇か圧力減少(もしくは両方)を受けたことを示唆する。コランダムの形成は分解反応の逆の条件(温度下降か圧力上昇)やざくろ石パイロキシナイトと共存するような比較的高圧条件が考えられる。後者の条件からはガブロ(=GBII)が高圧変成作用を受け,その後にマントルダイアピルの一部としてかんらん岩体とともに上昇してきた可能性が示唆される。

著者

中里 浩也 大場 孝信 板谷 徹丸

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.91, no.1, pp.1-10, 1996 (Released:2006-12-13)

参考文献数

14

被引用文献数

6 8

---

The geology and K-Ar geochronology of the Gassan volcano in Northeast Japan were carried out to establish the volcanic history.     This volcano is belonging to the Chokai volcanic zone, and composed of several volcanic edifices. On the basis of the field geology and K-Ar dating of the ejecta, the volcanic history is divided into five stages;      Stage I (0.88 Ma): the Amamoriyama was formed by dacite volcanism. The dacite lava is composed with hypersthene, augite, hornblende, biotite and quartz phenocrysts.     Stage II (0.7 Ma): The Yudonosan, which is composed of a stratovolcano and two lava domes of mainly dacite lava and pyroclastics.     Stage III: The volcanism occurred in the north of the Yudonosan. The dacite lava and pyroclastics covered on the basements in the caldera and the lower Yudonosan lava in the Ishihane river.     Stage IV (younger than 0.6 Ma): The volcanism of the major stratovolcanoes of central Gassan, the Waratahageyama and the Ubagatake, which are composed of lavas and pyroclastics. The rocks are calc-alkali andesite containing hypersthene, augite, sometimes a small amount of olivine and rarely hornblende.     Stage V: The collapse of the northwestern half of Gassan stratovolcano, caused the formation of a horseshoe-shaped caldera and dry avalanche deposits.     The rocks of the Gassan volcano are divided into two groups, dacite and andesite in their temporal as spatial distributions.

著者

田辺 行雄 柴草 英彦 平島 崇男

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.88, no.10, pp.463-468, 1993-10-05 (Released:2008-03-18)

参考文献数

7

被引用文献数

3 3

---

A BASIC program to calculate the Schreinemakers' bundle is designed for NEC 9800 series computer. Algorithms for determining stable univariant lines and combing stable invariant points are newly devised following the graphic theory. The computer program can solve all possible sets of invariant points in model systems with up to (C+5) phases. For model (C+3) phases systems, the program automatically displays all possible nets on a video screen.

著者

牧嶋 昭夫 中村 栄三

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.88, no.11, pp.499-516, 1993-11-05 (Released:2008-03-18)

参考文献数

69

被引用文献数

3 3

---

In this paper (Part I), recent progress in U-Pb dating of zircon is reviewed. Rare-earth element (REE) partitioning of accessory minerals and REE geochemistry of zircon will be reviewed in separate papers, Part II and Part III, respectively. Zircon (ZrSiO4) is one of the most important minerals in geochronology because the zircon crystal is very resistant to alteration, metamorphic and magmatic events. Zircons therefore preserve their primary chemical properties, especially very high U and Th and extremely low Pb contents, in many cases, resulting in most Pb in zircon to be time-integrated radiogenic origin. For the above reasons, zircon has been extensively used in geochronology for over 30 years. Conventional U-Pb dating of zircon has been performed using a thermal ionization mass spectrometer with isotope dilution (IDTIMS). With improvements in the techniques for the elimination of discordant parts and the chemical decomposition of zircon, it is now possible to measure U-Pb age with IDTIMS not only of a sircon grain but also of fragments of a single zircon grain. Recently, the single zircon evaporation technique has been developed to analyze for U/Pb only the closed-system domains in a single grain without chemical treatment. The most outstanding advance in U-Pb dating of zircon has been achieved by the development of secondary ion mass spectrometry (SIMS). Using the SHRIMP (Sensitive High Resolution Ion Micro Probe) at Australian National University, a very small area (<40, μm) can be analyzed, making it possible to reveal with precise age determinations the multiple growth history in a single grain of zircon. However, one of the major problems in the SIMS analysis resides in preparation of a homogeneous zircon standard. The U and Pb concentrations and the Pb isotope ratios of the standard must be known but they can only be obtained by the conventional IDTIMS method. The conventional IDTIMS is, therefore, a prerequisite for SIMS U-Pb dating. The oldest zircons, recorded >4.OGa, have been found with SHRIMP. The existence of such old zircons was confirmed by results obtained by IDTIMS and the single zircon evaporation technique with TIMS. Characterization of the latent primitive crust, based on the chemical compositions of the detrital zircons and their measured ages, has been attempted.

著者

松原 聰 加藤 昭

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.88, no.11, pp.517-524, 1993-11-05 (Released:2008-03-18)

参考文献数

10

被引用文献数

1

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愛知県新城市中宇利鉱山の旧坑からgaspeite, glaukosphaerite, mcguinessiteおよびjamboriteを発見した。 Jamboriteは鉱山付近の瓶割峠の採石場からも発見された。GaspeiteはCo/(Ni+Co)=0.28-0.31, glaukosphaeriteはNi/(Ni十Cu)=0.42~0.49, CoO 5% (重量)程度まで含む。これらの種では含Co変種は最初の発見である。Mcguinessite中ではMg/(Cu+Mg)=0.61~0.65で原記載より高い値を示す。瓶割峠産のJamboriteはFe/(Fe+Ni)=0.29~0.32で,化学組成変化をFeに富む側に拡げている。これらはすべて蛇紋岩を切る割目に着生する皮膜をなし,成因的に循環地表水と関係がある。これらの中の金属元素はその起源を皮膜下の含Ni蛇紋石, heazlewoodite, cobaltpentlanditeおよびdjurleiteによっているように見える。これらの炭酸塩中でのNi2+に対するCo2+の置換関係はこのような固溶体が容易に生成される旧坑内の条件下での地球化学的挙動の類似性を暗示している。

著者

宮下 敦 今井 直哉

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.89, no.6, pp.227-232, 1994-06-05 (Released:2008-03-18)

参考文献数

10

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Fine lamellar textures with chemical contrast are found in anisotropic grandite garnet from the skarn at the Kamaishi mine, Iwate Prefecture. The lamellae are charaterized by enrichment of iron; i. e., the compositional difference between lamellae and matrix amounts to 5 to 10 mole % in andradite molecules. In the sections sliced normal to (110) faces of garnet, the development of lamellae showing orientation parallel to (111) nearly normal to the growth zoning paralell to (110) face. Furthermore, the fine compositional bands (parallel to (110) growth zoning) are observed cutting the (111) lamellae clearly. The data cannot confirm that formation of lamellae normal to (110) occurs in subsolidus or not. However, the compositional band parallel to (110) is obviously results of subsolidus decomposition.

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

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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

高木 秀雄 柴田 賢 内海 茂

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.84, no.1, pp.15-31, 1989-01-05 (Released:2008-03-18)

参考文献数

38

被引用文献数

5 5

---

Various metamorphic rocks such as amphibolites (garnet-cpx amphibolite, schistose amphibolite, kyanite-bearing amphibolite), pelitic and basic schists (epidote amphibolite), and ultramafic rocks (spinel lherzolite, pyroxenite, hornblendite) are exposed in the Yoshimi Hills, to the east of the Kanto Mountains. Schistose amphibolites, which have the largest exposure in the Yoshimi Hills, and pelitic schists were moderately suffered mylonitization. The chemical composition of metamorphic minerals such as garnet, cpx and hornblende in the garnet-cpx amphibolite, and garnet in the schistose amphibolite suggests that these rocks were formed under the amphibolite to the granulite facies. The garnet-biotite temperature after Pigage and Greenwood (1982) estimated on the pelitic shcists is more than 800°C, considerably higher than the temperature (610°C) estimated on the pelitic schists in the highest metamorphic grade zone of the Sanbagawa belt in the Shikoku region. K-Ar ages of hornblende are 63.5 Ma for the garnet-cpx amphibolite and 61.0 Ma for the kyanite-bearing amphibolite, whereas K-Ar age of muscovite for the pelitic schist is 34.1 Ma. Form these age data, even though taking a possibility of rejuvenation into consideration, it is difficult to correlate the metamorphic rocks of the Yoshimi Hills to the metamorphic rocks of the Kurosegawa belt. Considering the occurrence of tectonic blocks of various amphibolite masses in the Sambagawa belt in the Shikoku region, it is possible to correlate the metamorphic rocks of the Yoshimi Hills to those in the Sambagawa belt. However, further study is necessary before we come to decide the belongings of the metamorphic rocks in the Yoshimi Hills.

著者

廣井 美邦 小林 栄一

出版者

日本鉱物科学会

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.91, no.6, pp.220-234, 1996 (Released:2006-11-25)

参考文献数

56

被引用文献数

4 6

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Three polymorphs of Al2SiO5, andalusite, kyanite and sillimanite, occur in contact with each other, forming aggregates in a part of the Nishidohira pelitic metamorphics in the Hitachi area of the southernmost Abukuma Plateau. Textural relationships between the three polymorphs suggest that andalusite formed first probably as chiastolitic porphyroblasts, that kyanite and/or sillimanite grew subsequently at the expense of pre-existing andalusite, and that sillimanite continued to form even in the rock matrix thereafter. The andalusite-forming first stage may have been either a contact metamorphic event by unknown plutons or a regional metamorphic event of low-pressure type. The second kyanite and/or sillimanite-producing stage was induced by high-temperature loading, whereas the third sillimanite-forming stage possibly resulted from the contact metamorphism by the Nishidohira gabbroic intrusion exposed near Hase. Well-preserved growth zoning of garnet containing sillimanite inclusions in the andalusite-kyanite-sillimanite-bearing gneisses also indicates the high-temperature compression. The loading may be attributed to the overthrusting of the nearby Hitachi metamorphics onto the Nishidohira metamorphics. Such a P-T path of the Nishidohira metamorphics is similar to that of the Takanuki metamorphics in the central to southern part of the Abukuma Plateau. The widespread occurrence of texturally sector-zoned garnet in pelitic-psammitic rocks and the inferred short duration of high-temperature conditions are also in common to the Nishidohira metamorphics and the Takanuki metamorphics.

著者

新城 竜一 伴 雅雄 斎藤 和男 加藤 祐三

出版者

日本岩石鉱物鉱床学会

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.86, no.7, pp.323-328, 1991-07-05 (Released:2008-03-18)

参考文献数

29

被引用文献数

10 11

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High magnesian andesites from Kume-jima and Iriomote-jima, the Ryukyu islands were dated by the K-Ar method with the basalts from Kobi-sho and Sekibi-sho, the Senkaku islands. The obtained K-Ar ages of the high magnesian andesites are 6.08 ± 0.46 Ma and 13.1 ± 1.1 Ma for the sample (s) from Kume-jima and Iriomote-jima, respectively. The volcanic activity of the high magnesian andesite magma continued intermittently for at least 6 Ma. The K-Ar age of the basalt from Sekibi-sho is 2.59 ± 0.19 Ma. The age of the basalt lava from Kobi-sho is as young as 0.2 Ma or even younger, and indicates that Kobi-sho is a Quaternary volcano.

著者

牧野 州明 山口 佳昭 冨田 克敏

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.91, no.11, pp.419-423, 1996 (Released:2006-10-28)

参考文献数

16

---

Fluor edenfite was found in cavities of the Ishigamiyama lava dome building two pyroxene-hornblende-andesite in the Kimpo volcano, Kumamoto, southwest Japan. The fluor edenfite is associated with tridymites and magnetites in the cavities. This is the first description of volcanic fluor-amphibole, and its chemical analysis was made by combining microprobe, vacuum-heating method and Mössbauer spectroscopy. The Ishigamiyama fluor edenite has 1.47F, 0.13OH, 0.03Cl and 0.37O pfu in the O3 site, and thus, is characteristically poor in (OH). This edenite is the most F-rich one in edenites and edenitic hornblendes previously reported.

著者

代 開秋 津末 昭生 本間 弘次

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.88, no.5, pp.247-264, 1993-05-05 (Released:2008-03-18)

参考文献数

40

被引用文献数

5 5

---

From the mode of occurrence, texture, and mineral assemblage, granitic rocks in the Kashiwa-jima-Okinoshima district are classified into four groups; namely, the Tanijiri-type granodiorite (abbreviated to TGd), the Tanijiri-type granodiorite porphyry (TGdp), the Moshima-type medium-grained granite (MmGr), and the Moshima-type fine-grained granite (MfGr). The similarity of major and trace element chemistry of the TGd and TGdp, and of the MmGr and MfGr suggests that the petrogenetic processes operating were similar, respectively. The Rb-Sr isotopic analyses of nine whole-rock samples of the Moshima-type granitic rocks (MmGr and MfGr) yield an age Rb-Sr of 16±2 Ma with an initial 87Sr/86Sr ratio of 0.70740± 0.00018. From the data of Nd and Sr isotopic ratios (Fig. 9) and of initial 87Sr/86Sr ratios and reciprocals of the strontium concentration (Fig. 10), it is suggested that the Tanijiri-type granodioritic rocks have been formed by mixing of an original S-type magma and sedimentary rocks of the Shimanto belt, while the Moshima-type granitic rocks have been formed by fractional crystallization of a S-type magma, which has been more felsic than the original S-type magma. From the chemical composition of garnet in the TGdp, it is suggested that the original S-type magma of the Tanijiri-type granodioritic rocks may have been generated by the partial melting of metamorphic rocks of pelitic and psammitic origin at a depth of about 20km. The TGdp shows a distinct porphyritic texture compared with the TGd. Minerals, such as plagioclase, orthopyroxene, cordierite, and biotite in the TGd have slightly wider range of solid solution compared with the minerals in the TGdp. Therefore, it is suggested that the petrogra-phical difference between the TGd and TGdp may have been caused by a difference in the ascent and cooling rate of their magmas.

著者

土屋 範芳 鈴木 舜一 小田 幸人 飯島 章夫

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.84, no.3, pp.89-96, 1989-03-05 (Released:2008-03-18)

参考文献数

44

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Carbonaceous material in pelitic rocks and limestones of the Ayukawa and the Daioin Formations in the Hitachi metamorphic rocks was investigated by means of X-ray powder diffraction technique. Carbonaceous material in these metasediments was graphitized under the conditions of greenschist facies. rystallite thickness Lc (002) ranges from 29 to 170 Å in the Ayukawa Formation and that from 120 to 300 Å in the Daioin Formation. Lc (002) of carbonaceous material in pelitic rocks containing biotite is more than 60 Å and increases with increasing metamorphic grade. Lc (002) value at a boundary between greenschist and epidote-amphibolite facies may be estimated 260-300 Å from the data of Lc (002) of the lower part of the Daioin Formation. Lc (002) of the Ayukawa Formation surrounding the sheared granite is above 200 Å. As compared with the general value of the Daioin Formation, Lc (002) of the Daioin Formation around the sheared granite is not so high. Thermal effect of the sheared granite was not marked, which suggests that the sheared granite intruded under low temperature condition.

著者

大場 司

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.86, no.7, pp.305-322, 1991-07-05 (Released:2008-03-18)

参考文献数

16

被引用文献数

3 4

---

Geological survey has been carried out on Akita-yakeyama volcano, eastern Akita Prefecture, Japan to establish the evolutional history of the volcano. Furthermore, the volcanic products have been described in detail to contribute to the petrological investigation of the volcano, that is currently in progress. The volcanic activities can be divided into three stages in terms of mode of volcanic activity or characteristics of the erupted products, or both. Approximately 300, 000 years ago, the volcanic activity started within a caldera formed by the eruptions of the voluminous felsic pyroclastics at 1 million years ago. This is the beginning of the early stage; the new volcano erupted number of andesitic lavas of the pigeonitic rock series while pyroclastic flows and falls were less abundant. The shape and size of the volcano built during this stage is not clear since it was covered with the following volcanic products, and severe erosion altered it much. In the middle stage the lava flow activities have been associated by explosive eruptions: pyroclastic falls and flows were repeated from central vent. The alternation of lavas and pyroclastics could have completed a large stratovolcano. All the volcanic rocks during this stage belong to hypersthenic rock series. After middle stage, the activity ceased for a while, and hydrothermal alteration expanded to nearly all over the volcano. Consequently, collapses of the altered piles of lavas and pyroclastics have led to five horseshoe-shaped calderas around the summit. After the repose period, the late stage activity started with explosive central and flank eruptions of pyroclastic fall; lava flows as well as pumice falls followed. During this stage, two andesite lava domes and two dacite domes were constructed. In the central area of the summit crater a dacite dome was built and dacitic ash was erupted; this is the latest activity. All the rocks of the last stage are of the hypersthenic rock series as well.

著者

横瀬 久芳 山本 茂

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.91, no.3, pp.86-101, 1996 (Released:2006-12-13)

参考文献数

25

被引用文献数

3 4

---

To understand the character of deep-seated crustal components, we have investigated the crustal xenoliths, in Pleistocene andesites from the Kinbo volcano, northwest Kyushu, Japan. Various types of rocks, such as gneiss, Px granulite, Ho-Pl amphibolite, hornblendite, Ho±Cpx gabbro and granitoids, are found as crustal xenolith in the andesites. The average chemical compositions of the crustal xenoliths in Araoyama and Ishigamiyama are similar to those of tholeiitic basalt and basaltic andesite, respectively.     There is no interaction zone between the xenoliths and host andesites in their appearance indicating that the thermal difference between them was small at entrainment. However, complex disequilibrium textures, including breakdown of hydrous minerals, plagioclase with sieve texture and quenched anatectic melt, occur in thin section of almost all the samples. These textures indicate that pyrometamorphism of the xenoliths resulted from the heating of basaltic magma erupted at early stage of the volcano. The parent rocks, eliminating the influence of pyrometamorphism from the xenoliths, presumably equilibrated under amphibolite facies condition, and were heterogeneous basic gneiss as a whole. Based on the lithologic and chemical character of the basic gneiss combined with reported geophysical data in this region, it is expected that the basic gneiss may widely distribute as the crustal components under the Conrad discontinuity in the northwest Kyushu.

著者

片田 正人 高橋 一男 藤原 郁夫

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.86, no.3, pp.91-99, 1991-03-05 (Released:2008-03-18)

参考文献数

6

被引用文献数

1 1

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The Himekami pluton is a complex of mafic rocks and their differentiated felsic rocks, which belong to shoshonite rock association. The pluton is devided into three bodies: South pluton, North pluton and Shiroishi pluton. The South pluton, consisting mainly of monzonite, monzogabbro, quartz monzonite and quartz monzodiorite, is classified genetically into four groups of mafic and felsic rocks. Each rock group accompanies a few amounts of xenolithic mass of cumulated, ultramafic rocks and melagabbro. The North pluton is a zoned pluton of quartz monzonite, granite and granodiorite. The Shiroishi pluton is a leucocratic tonalite-granodiorite.

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

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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

井ノ上 幸造

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.83, no.1, pp.26-41, 1988-01-05 (Released:2008-03-18)

参考文献数

29

被引用文献数

11 10

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Takachiho composite volcano, located in south Ky ?? sh ??, Japan, is one of major members of the Kirishima volcano group. The composite volcano consists of four volcanic edifices which are partly overlapping and aligned in E-W direction. On the basis of field geology and tephrochronology, its growth-history can be divided into four stages. During the first stage, a conical stratovolcano, Futagoishi, was formed in the eastern end of the composite volcano. It is com-posed of an alternation of pyroclastic beds and lava flows. The activity of Futagoishi ended before the eruption of Ito pyroclastic flow deposit (22, 000 yBP) from the Aira caldera. The second stage activity started about 10, 000 years ago, after a repose of more than 12, 000 years. It was characterized by vulcanian eruption which continued semi-persistently through a long period of time, probably more than a thousand years. During this period a stratovolcano, Old-Takachiho, was built up on the western flank of Futagoishi, and a large amount of volcanic ash accumulated concentrically around the volcano. The third stage activity was characterized by the eruption of several thin lava flows and scoria from the vent close to Old-Takachiho Volcano. This activity resulted in formation of a small conical stratovolcano, Takachiho-no-mine, on the western slope of Old-Takachiho. At the end of this stage, enormous lava flows were successively effused from the top crater and flowed downward widely. Later lava flows, however, did not reached the foot of the slope due to decrease in effusion rate and piled up around the crater, resulting in the construction of an exogeneous lava dome on the summit. After several hundred years of quiescence, the present stage activity began about 2, 500 years ago. This activity was characterized by sub-plinian eruptions which occurred intermittently and produced thick scoria and ash beds on the eastern foot of the composite vlocano. By repeated eruptions of a great volume of scoria and lava flows, a new vlocano, Ohachi, was born on the western flank of Takachiho-no-mine volcano, and has been active since then. The growth-history of Takachiho composite volcano revealed the following two features: 1) the volcanic activity may have been controlled by the underlying E-W fracture, as suggested by the shifting of the vent position from east to west, and 2) the styles of explosive activity of the composite volcano have gradually changed with time from vulcanian eruption to sub-plinian one.

著者

鈴木 五百紀 秋月 瑞彦 長瀬 敏郎 藤巻 宏和

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.90, no.4, pp.124-131, 1995 (Released:2006-12-26)

参考文献数

42

被引用文献数

1 1

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Orbicular rock from Inusotoba, Shiroishi, Miyagi Prefecture was studied by optical and chemical methods. The orbicules, which are 5∼20 cm in diameter, are divided into two parts, — core and shell. The core is ball-shaped and dark-colored, and consists mainly of fibrous hornblende and chlorite. The shell, which surrounds core, is light-colored and consists of coarse radial anorthite crystals less than l cm long, which are elongated to a-axis. These radial crystals are characterized by micro subgrains of albite twin and parallel-growing crystals. The other type of orbicule is also known, whose shell consists of several alternate layers of mafic and felsic minerals. This latter type of orbicules is never produced together with the former radial type. The matrix, solidified among orbicules, has a heterogeneous texture, which consists of the dark-part of poikilitic hornblende and the light-part rich in euhedral plagioclase.     The forming environment of orbicular rocks is featured by many close-packed orbicules, the flow structure of felsic mineral assembledge in matrix and unmixing of magma including orbicules with the other magma containing plagioclase spherulites. It is considered that orbicules were formed in supercooling magma possibly due to income of another magma.