地球科学

弧状列島について(<特集>弧状列島)

山下昇

原稿種別: 本文
1963 年 1963 巻 65 号 p. 1-13
発行日: 1963/03/25
公開日: 2017/07/24

DOIhttps://doi.org/10.15080/agcjchikyukagaku.1963.65_1

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This article is largely devoted to the historical review of researches concerning island arcs (Chapters I-III). In Chapter IV, such a writer's opinion as follows is presented briefly. 1. The Fossa Magna-Shichito-Bonin Arc, which is apparently younger than the Honshu Arc, is a manifestation of a certain deep seated zone of boundary dividing certain units also buried deep in the earth's mantle. The units and the boundary zone are thought to be of very ancient origin. Underlying the Palaeozoic geosyncline and the later geanticlines and geosynclines of the Honshu Arc. they had affected the Palaeozoic and Mesozoic history of the Honshu Arc, thus exhibiting various differences in rock facies, thickness of deposits, igneous activity and in time and magnitude of crustal movement between Northeast and Southwest Japan. At the beginning of Neogene epoch, the deep seated zone of boundary manifested itself resulting in the Fossa Magna. 2. A layered structure of the earth's mantle is probably the best solution of this problem. The low-velocity layer of GUTENBERG and the discontinuous distribution of deep earthquake foci in the vertical section suggest also the layered structure. Each layer is, further, divided into segments of varied horizontal extension, larger and polygonal below continents and oceans and smaller and elongated below the orogenic belts. 3. The significance of the Palaeogene-Neogene boundary and of the Neogene crustal development is very great so far as the western Pacific island arc province is concerned. The Neogene history in these areas is essentially independent of the preceding Palaeogene and Mesozoic history, though some tendencies to conform to the older elements are apparent.

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東京大学における「岩石磁気研究グループ」の研究活動の概要(<特集>弧状列島)

小島稔

原稿種別: 本文
1963 年 1963 巻 65 号 p. 20-23
発行日: 1963/03/25
公開日: 2017/07/24

DOIhttps://doi.org/10.15080/agcjchikyukagaku.1963.65_20

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過去20数年にわたり,東大理学部地球物理教室の永田研究室を中心とする"岩石磁気研究グループ"は,岩石磁気の基礎的性質およびその応用としての古地磁気学の研究を行ってきた.榛名山産の軽石に発見された自己反転残留磁気およびこの物理的機構の解明,FeO-TiO_2-Fe_2O_3系磁性の組織的研究,箱根・伊豆地方の第四紀火山における古地磁気学研究,また最近にいたり,Inverse Thermo-Remanent Magnetism(I.T.R.M.), Thermo-Crystalline Remanent Magnetism(I.C.R.M.)の発見など,おもな研究成果の例としてあげられよう.最近,川井らの提唱した"第三紀における日本列島屈曲の仮説"なども,古地磁気学を地球科学の面に,積極的に応用した例である.

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地質現象のエネルギー解析(<特集>弧状列島)

地球の進化を熱力学的にあつかうための一手段として

島津康男

原稿種別: 本文
1963 年 1963 巻 65 号 p. 24-32
発行日: 1963/03/25
公開日: 2017/07/24

DOIhttps://doi.org/10.15080/agcjchikyukagaku.1963.65_24

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A program for a thermodynamical study of terrestrial evolution is proposed. The evolution is described by a coupling among various thermodynamical non-equilibrium states (dynamical, gravitational, thermal and chemical). Geological processes, i.e. a secular variation of crustal state, is a typical manifestation of evolution and it can be analyzed from thermodynamical view point. A method of energy analysis of geological phenomena is described and is applied to tectogenesis within the area of South-Western Japan since Mesozoic era. The driving energy of tectogenesis, which is appeared to be supplied by a form of abnormal heat flow from the upper mantle is estimated as 2×10^<31> ergs. If the process of tectogenesis is regarded as a heat engine, the efficiency becomes several percent. The greater part of the supplied energy is consumed as a formation process of Chugoku granitic batholith. The rate of energy supply must be several times of normal heat flow the mantle through Moho. The result of preliminary analysis for a so-called GreenTuff stage during Tertiary era reveals that the rate of energy supply is the same order of Mesozoic tectogenesis. An apparent difference in features between processes within South-Western and North-Eastern Japan is discussed based upon the results of energy analysis. It seems that a role of upper mantle as an energy source is different between them. In the former the mantle is a simple energy source which derives mainly the remelting of the crust. In the latter, on the other hand, the upward transfer of basaltic magma is predominant. A detailed analysis should be performed by a method of numerical experiment using a highspeed computer.

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霧ガ峯,荒船山地区における鮮新世火山活動II

フォッサ・マグナ帯中央部における瀬戸内区の延長

河内晋平, 河内洋佑

原稿種別: 本文
1963 年 1963 巻 65 号 p. 33-37
発行日: 1963/03/25
公開日: 2017/07/24

DOIhttps://doi.org/10.15080/agcjchikyukagaku.1963.65_33

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In the middle part of the "Fossa Magna", the basement rocks of SW Japan and of NE Japan are in syntaxis. The geologic history of the Kirigamine and the Arafune areas, which lie at the apex of the syntaxis and situate in intimate relation with the two NE-SW trending "green tuff" areas in the Northern "Fossa Magna" zone, is summarized with special reference to the volcanisms during Pliocene and Quaternary. On the basis of geologic history, geologic structure and petrography, it is concluded that the present areas are geologically the eastern extension of the "Setouchi" province of SW Japan.

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秋吉の赤色凝灰質頁岩の岩質

針谷宥, 大島和雄

原稿種別: 本文
1963 年 1963 巻 65 号 p. 38-39
発行日: 1963/03/25
公開日: 2017/07/24

DOIhttps://doi.org/10.15080/agcjchikyukagaku.1963.65_38

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秋吉・大久保附近に発達する赤色凝灰質頁岩(ナムル型の海性化石をふくむ)を鏡下で観察したのち,粒度分析を行い,さらに粘土鉱物などについて検討した.粒度分析の結果,コロイド状の部分の多いことを知ったが,分級はかなり良いものである.粘土質の部分についてのX線回折および示差熱分析の結果は,それが一般に結晶度の低い,ハロイサイトとモンモリロナイトの混合体であり,その他に微粒の石英をふくむことを示す.コロイドの部分は微粒の低結晶度のハロイサイトをふくむ.細粒砂は全構成物質の42.3%に達する.主として火山性ガラスと緑泥石化した斜長石から成る.全体として,中性火山岩または凝灰岩起源の頁岩である.

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