The Journal of the Geological Society of Japan

Geotectonies of the Pacific with reference to South-western Japan : I., Distribution of the two tectonic regions in Shikoku, manifesting the Pacific and the Japan Sea Movement (1)

S. EHARA, S. SAWATA

1955 Volume 61 Issue 717 Pages 231-239
Published: June 25, 1955
Released on J-STAGE: April 11, 2008

DOIhttps://doi.org/10.5575/geosoc.61.231

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Sur les rejets environs Ichinomegata dans Ia peninsule d'Oga (Prefecture d'Akita)

Hiroshi HAYASHI

1955 Volume 61 Issue 717 Pages 240-248
Published: June 25, 1955
Released on J-STAGE: April 11, 2008

DOIhttps://doi.org/10.5575/geosoc.61.240

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Il y a beaucoup de rejets pele-meles environs Ichinomegata., Les rejets essentiell se composent de nodule a olivine, de nodule a augite, de gravier volcanique a basalt et de ponce de dacite., Les rejets accidentiels sont granite, diabase, andesite, rhyolite, porphyrite dioritique, diorite, nodule a amphibole et plagioclase (gabbro, melagabbro et yamaskite) et roches sedimentaires., Les graviers volcaniques a basalt se composent de granite et de nodule a olivine comme des enclaves., Ces granites auront recu le metamorphisme., Donc la poche fluide limitee se trouve environs le granite du soubassement et auront contamine par le granite., Le magma original est riche en aluminium et pauvre en calcium., Donc le nodule a olivine n'a aucune trace de plagioclase., 1) Le differentiation magmatique y serait comme suivant: nodule a olivine nodule a augite basalt Magma original Differentiation de gravite granite contamination 2) Par I'analyse spectroscopique, il est demontre que I'olivine dans la nodule a olivine est de la meme composition que celle dans Ie basalt., 3) Suivant l'analyse chimique de cobalt et de nickel, le rapport Ni : FeO n'est pas grand l'olivine de roche plutonique, mais il est considerable dans celle du nodule a olivine., Donc le nodule a olivine dans Ichinomegata est le produit de differentiation de gravite dans le poche fluide limitee.,

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On the Geologic Structure and the Volcanic Activity of Himesima, Oita Prefecture

Taro KASAMA, Kazuo HUZITA

1955 Volume 61 Issue 717 Pages 249-257
Published: June 25, 1955
Released on J-STAGE: April 11, 2008

DOIhttps://doi.org/10.5575/geosoc.61.249

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Himesima, small island situated near the western border of the Inland Sea., B., KOTO'S paper "On the Volcano of Japan" (1916) has attracted the attention of many petrologists concerning the volcanic rocks in this island., Since the publications, though a few works on the petrology of the volcanic rocks has been reported by the other authers, but no study has been published from the stratigraphic point of view., The present paper is chiefly devoted to the description of the late Cenozoic sediments of this island, with special reference to the geologic structure and the age of the volcanic activity The stratigraphic sequence is summarized as follow: Himesima volcanics and tuff breccia unconformity Himesima formation Karato member (70m+) Maruisihana member (60+) Basement rock unexposed The Maruisihana member contains conspicuous amounts of pyroclastic materials and the uppermost part consist of a thick volcanic conglomerate, by which the Himesima formation is divided in to two members., These materials contain bear hornblend-andesite which is characteristic in the "Sanin Volcanic Zone"., On the contrary, the Karato member consists of an alternation of sand and mud containing little pyroclastic materials., The Himesima formation may be correlated with the neighbouring Turusaki formation which is considered to be early Pleistocene (I₂) in age., The geologic structure of the Himesima formation is characterized by the marked folding with axes running nearly N-S direction., Some parts are remarkably modified by the volcanic bodeis intruding anlong the anticlinal axes as shown in Fig., 3., The Himesima volcanics and tuff breccia rest on the Himesima formation unconformably and build up five cones., The age of this activity may be assigned to late Pleistocene (J₂∼J₃).,

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Stratigraphical Study on the Nishiyatsushiro Group (Miocene) in the Area of the Upper Stream of the Fuji, Japan

Tokihiko MATSUDA, Atsuyuki MIZUNO

1955 Volume 61 Issue 717 Pages 258-273
Published: June 25, 1955
Released on J-STAGE: April 11, 2008

DOIhttps://doi.org/10.5575/geosoc.61.258

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The geosynclinal sediments (Late Cenozoic) which comprise much Volcanic products, are developed in the South Fossa Magna, Central Japan, and are intensively deformed by later crustal movements., In this paper, the Nishiyatsushiro group, one of the representatives of these sediments, is described and some problems are discussed., 1 The group consists mainly of pyroclastics and mudstone-rich alternations, and is divided into the following four formations: (Shizukawa group)., ., ., ., ., ., ., ., ., unconformity (?)., ., ., ., ., ., ., ., ., Nishiyatsushiro group Shimobe formation., ., ., ., ., ., ., ., ., mostly of an alternation of sandstone and mudstone with fine conglomerate beds., The upper part is cut off by a fault., Daigoyama formation., ., ., ., ., ., ., ., ., basic (lower) and acidic (upper) pyroclastics, sandstone and mudstone., The lower part consists of basalt and basic tuffaceous sandstone, and the upper of pumiceous tuff, sandstone and mudstone., Ichinose formation., ., ., ., ., ., ., ., ., mostly of mudstone and alternated acidic tuff., Alkaline olivine basalt occurs in the lowest part as thin lavas and sheets., Furusekigawa formation., ., ., ., ., ., ., ., ., mostly of basic lavas and pyroclastics with thin tuffaceous sandstone and mudstone., The base is unknowxn., (in descending order) Besides the above, two mudstone members are intercalated between the Daigoyama formation and the Shizukawa group, but their stratigraphical position remains unsettled., 2 In the area where the group is exposed, igneous activities are represented in the following sequence in ascending order., 1) A large amount of tholeiitic (pigeonitic according to H., KUNO) basalt acompanied with a small quantity of alkaline olivine basalt (in the upper horizons)., 2) Subordinate amount of acidic tuff alternating with mudstone and other sediments., 3) Acidic intrusives 4) Calc-alkalic (hypersthenic according to H., KUN0) andesite eruptives (in the shizukawa group)., It is remarkable that similar sequences of igneous activities and associated sediments are found in the other areas within the South Fossa Magna regions., 3 The group is probably Miocene in age., There are few fossils except Sagarites and small foraminifers., 4 Alteration of the igneous rocks is comparatively slight., The texture of the rocks and most of the rock-forming minerals are fairly well preserved., However, all of olivine and some of hypersthene and plagioclase are altered., Iron saponite is most conmon as a secondary mineral., Chlorite, prehnite and epidote appear in the tuff only in the southeastern part contiguous to the area of many intrusive bodies which are not shown in the map.,

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New Discovery of the Molars of Mammonteus primigenius BLUMENBACH from Erimo-misaki, Hokkaido

M. MINATO, S. IGI, T. KAKIMI

1955 Volume 61 Issue 717 Pages 274a
Published: June 25, 1955
Released on J-STAGE: April 11, 2008

DOIhttps://doi.org/10.5575/geosoc.61.274a

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Lepidocyclina nipponica from the Ochiai Formation at the East-margin of the Tanzawa Massif

Keizo MIKAMI

1955 Volume 61 Issue 717 Pages 274b-275
Published: June 25, 1955
Released on J-STAGE: April 11, 2008

DOIhttps://doi.org/10.5575/geosoc.61.274b

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