10 0 0 0 OA 伊豆半島蛇石火山熔岩の主成分化学組成
蛇石火山は伊豆半島南西部に位置する第四紀火山で, その噴出物は東西3km, 南北6km にわたって分布する。この火山体は第三紀中新世後期の白浜層群を不整合に覆って形成された。火山体を構成する岩石は, 岩相・層位学的にみて, 大きく2つのユニット(下部ユニットと上部ユニット)に区分される。下部ユニットは火山体の主要部分を構成するもので, 熔岩流と火砕岩からなり, 約150m の厚さをもつ, 上部ユニットは数10m の厚さで, 陶汰の悪い熔岩の角礫を含む堆積物からなる。下部ユニットは北部の高地と南部の海岸付近に, 上部ユニットは間の比較的平坦な地形の部分に分布する。 下部ユニットの熔岩のうち, 南部の落居付近にみられる7枚と北部の大峠付近の3枚について岩石記載を行った。岩石はすべて(かんらん石)-紫蘇輝石-普通輝石安山岩である。岩石9試料のモード, 主成分を分析した。熔岩が噴出したときのメルトと結晶の量化は3 : 2∿3 : 1で, 後に噴出した熔岩ほどΣFeO, MgO, CaO に乏しく, SiO_2に富む。しかし, 全体としては化学組成の変化の範囲は比較的狭く, 結晶分化作用があまり進行しないまま, 短期間に熔岩の流出が行われたとす推定される。鉱物組定・化学組成からみて, 蛇石火山の岩石はカルク・アルカリ岩系に属し, ノルム石英を10vol.%以上含むことから, 伊豆半島南西部の第四紀火山の溶岩のなかで SiO_2に最も過飽和であるといえる。
2 0 0 0 OA 南部北上山地, 世田米地域の古生層について
- 著者
- 斎藤 靖二
- 出版者
- 東北大学
- 雑誌
- 東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)
- 巻号頁・発行日
- vol.62, pp.55-67, 1966-03-30
The Paleozoic System distributed in the Setamai district, southern Kitakami massif, is classified on the ba-5is of rock facies as follows; Toyoma Formation Permian Kanokura Formation Sakamotozawa Formation ~Unconformity~ Nagaiwa Formation Onimaru Formation Carboniferous ~Unconformity~ Odaira Formation Arisu Formation Orikabe Formation The Orikabe, Arisu, and Odaira Formations are composed chiefly of "schalstein" and black slate. The acidic to andesitic pyroclastics intercalated in the Orikabe Formation indicate the former existence of volcanic activities. The Arisu Formation and the lower part of the Odaira Formation are composed mostly of andesitic pyroclastics, which decrease in thickness upwards to the middle part of the Odaira Formation. This shows that intense volcanism was periodic during deposition of those formations. The formations other than mentioned above do not show such intense volcanic activity. The Paleozoic System of this area is folded and faulted into blocks and thus their structures are complicated. The Hizume-Kesennuma tectonic line which extends in NNW-SSE direction is situated in the western part of the area and the eastern margin is defined by the grandodiorite which metamorphosed the sedimentaries in contact ther with. The most striking feature of the geology of this district is the structural differences between the Carboniferous and the Permian Systems. This unconformity was discovered by Minato (1942) at the base of the Permian Sakamotozawa Formation in the Setamai district who said that it represents the "Setamai folding" of thee Late Carboniferous. The folding axes of the Carboniferous System trend nearly N-S, whereas that of the Permian System is generally NNW-SSE in direction, being parallel with the Hizume-Kesennuma tectonic line. The Permian System is distributed in the northeastern, southeastern and central parts of the district and along the tectonic line. In the central part, in general, the Permian strata form a large-syncline, with NNW-SSE trend plunging to the south and parallel with the tectonic line. On the other hand the Carboniferous System which is restricted in distribution to the eastern side of the tectonic line, is developed on the outerside of the large-syncline. In the east of Komata it occurs in the Permian System as a block uplifted by faulting. The Orikabe Formation is distributed along the western wing of the syncline extending from Orikabe to Okuhinotsuchi in north to south direction though it is separated into several blocks by faults. The Arisu Formation is developed on the outerside of the Orikabe Formation which follows the syncline. The Odaira Formation is distributed generally farther to the outerside than the lower formations though it is directly overlain with unconformity by the Sakamotozawa Formation at the west of Mt. Odaira, and is bordered by the Onimaru Formation on its outerside. Concerning the Carboniferous System it seems that each of the formations is developed on the westward and eastward sides of the central part of the area in ascending order, and all of them are covered with unconformity by the Permian Sakamotozawa Formation. Furthermore, the Carboniferous System sometimes develops a large-anticline and gently dipping fluted homoclines, features which cannot be seen in the intensely folded Permian System. It seems that these evidences reflect not only the lithofacies but also the geologic structures of the Carboniferous System before the deposition of the Sakamotozawa Formation. The differences of the geologic structures between the Carboniferous and the Permian Systems, as mentioned above, are the results of the "Shizu folding" and the "Setamal folding" of Minato (1942). Therefore it is supposed that a large-anticline with axis of nearly N-S trend might have been formed and denuded in the Setamai district before the deposition of the Sakamotozawa Formation. The geological structures must have been fairly complicated, but concerning the details more precise investigation must be undertaken.
1 0 0 0 OA 琉球列島の自然史科学的総合研究 : 調査経過の概要と研究結果の要約
1 0 0 0 OA 自然と歴史の融合プログラム開発と新しい博物館教育-箱根火山と築城を例に-
1 0 0 0 OA 地球システム相互作用の理解に基づく地球史学習プログラムの構築
46億年にわたる地球史・生命史に関する情報を収集し、地球史・生命史イベントと地球システムの相互作用を理解するための総合年表の作成を進めた。当館が所蔵する標本や画像など各種資料のデータベースを再構築するとともに、それを補完する標本と資料の収集を進めた。それらを活用した地球史学習プログラムとして、常設展示の展示標本と解説資料を活用した、地球の歴史の中でおきた現象と地球システムについて理解できる双方向形式の連続講座を実施した。参加者が地球史・生命史について理解を深め、現在および未来の地球について考えることができ、地球科学リテラシーの涵養を図ることが出来る環境を提供できた。
1 0 0 0 OA 自然災害教育プログラムの開発による新しい博物館機能の開拓
1 0 0 0 仮想「日本自然史博物館」
- 著者
- 斎藤 靖二 小出 良幸 高橋 啓一
- 出版者
- Tokyo Geographical Society
- 雑誌
- 地學雜誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.107, no.6, pp.889-897, 1998-12-01