Journal of the Geological Society of Japan最新文献

{"title":"Kusatsu-Shirane volcano as a site of phreatic eruptions","authors":"A. Terada","doi":"10.5575/GEOSOC.2017.0060","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0060","url":null,"abstract":"This paper reviews the hydrothermal systems of Kusatsu-Shirane volcano, Japan, which are associated with phreatic eruptions. The existence of hydrothermal systems at this volcano is easily explained: hot springs are derived from unique thermal water that results from condensation of magmatic gas. Kusatsu-Shirane also exhibits fumaroles characterized by high H2S and CO2 contents, which are separate from the condensation of magmatic gas. Clay layers composed of smectites control the subsurface flow of thermal water. Hypocenter distributions of microearthquakes approach from depth to a bellshaped impermeable clay layer underlying the Shirane pyroclastic cone, indicating the clay layer’s role in storing thermal water supplied from depth. Sources of low-frequency earthquakes, ground deformation, and demagnetization/magnetization are located around the bell-shaped impermeable clay. These observations indicate that a hydrothermal reservoir exists under the clay layer. Phreatic eruptions seem to result from the growth of cracks connecting the reservoir to the surface. Precursory changes in volcanic activity precede phreatic eruptions at Kusatsu-Shirane in most cases; however, the contents of such precursors do not correlate with the ejecta mass, locations, and lead times of eruptions. Kusatsu-Shirane has been continuously monitored since the 1970s. The phreatic eruption of 1976 was predicted based on geochemical observations, but no precursor warning was detected before the onset of a series of phreatic eruptions in 1982–1983. Microearthquake swarms that occurred in 1989–91 and 2014 were followed by demagnetization and changes in the chemical composition of the water in Yugama Crater Lake and the fumaroles. These changes were similar to precursors of past phreatic eruptions at Kusatsu-Shirane, but no phreatic eruption occurred at Yugama Crater within 2–3 years of either set of changes. Multiparameteric monitoring, including geophysical and geochemical observations, is a powerful tool for detecting changes in volcanic activity, but it is difficult to identify precursors of phreatic eruptions.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133416746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Recent eruptions in Japanese Islands","authors":"T. Oikawa, K. Mannen, N. Geshi, S. Nakano","doi":"10.5575/GEOSOC.2018.0019","DOIUrl":"https://doi.org/10.5575/GEOSOC.2018.0019","url":null,"abstract":"","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123805149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Re-evaluation of explosive activities of Iwate Volcano in the last 10,000 years:: Spatial and temporal relationship of phreatic and magmatic explosions","authors":"J. Itoh, S. Hamasaki, Y. Kawanabe","doi":"10.5575/GEOSOC.2018.0009","DOIUrl":"https://doi.org/10.5575/GEOSOC.2018.0009","url":null,"abstract":"The active Iwate Volcano is located on the volcanic front of the Northeast Japan Arc. Yakushidake (2038 m), which is the youngest stratocone of Iwate Volcano, formed after a large-scale sector collapse associated with the Hirakasa debris avalanche deposit. This study re-examines the explosive eruptive history of the Yakushidake stratocone via tephra-stratigraphic study and radiocarbon dating. New C ages indicate that the Hirakasa debris avalanche occurred at 8.5–9.9 cal ka BP. Twelve phreatic eruption units (labeled here Iwph12 to Iw-ph1, from oldest to youngest) and one argillaceous pyroclastic density flow deposit (the Yunosawa pyroclastic deposit, YPD) were identified by detailed C age dating and X-ray diffraction mineralogical analyses. The average recurrence interval of phreatic eruptions is 500–1000 years. Phreatic tephra deposits crop out around the Yakushidake summit crater, the Ojigokudani fumarolic area, and the Amihariyumoto geothermal area. The thickest phreatic tephra deposit, Iw-ph7, was erupted from Amihariyumoto at 4.0–4.5 cal ka BP. An ashfall volume of ca. 2.3×10 m for the eruption was estimated using the calculation method of Hayakawa (1985). Explosive magmatic eruptions deposited 15 tephra units. Three of the more voluminous explosive units (Iw-SuS, Iw-OdS, and Iw-KS) eruptions have approximate magnitudes of VEI = 3 and were associated with the pyroclastic surge deposits. The repose interval between voluminous explosions is c. 2000 years. The volcanic history of Yakushidake Volcano is dominated by two vigorous eruptive phases: YV1 (associated with tephra deposits Iw-W6d to Iw-OkS) and YV2 (tephra layers Iw-SS to Iw-KS and KSr). In both phases, small-scale magmatic eruptions preceded the more voluminous (VEI = 3) events. There is evidence for recurrent phreatic activity during the vigorous eruptive phases; however, individual magmatic activities and phreatic eruptions do not always coincide.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127406260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geological study of phreatic eruptions","authors":"T. Oikawa, T. Oba, A. Fujinawa, Hisashi Sasaki","doi":"10.5575/GEOSOC.2017.0071","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0071","url":null,"abstract":"Phreatic (non-juvenile) eruptions are the most common type of magmatic activity on Earth. Here we review the characteristics of phreatic eruptions, which occur when overheated water is rapidly vaporized. Tephra layers produced by phreatic eruptions are composed mainly of clay-rich volcanic ash with variably altered lapilli and volcanic blocks. A single phreatic eruption can last between one hour and one day; however, eruptions may occur successively over a period of years to decades. The total volume of tephra produced by a phreatic eruption is typically 10m, maximum <10 m. Phreatic eruptions may be accompanied by diverse phenomena, including: tephra fallout, ejected rock fragments, low-temperature pyroclastic flows, and syneruptive-spouted type lahars. There are few detailed descriptions of low-temperature (~100°C) pyroclastic flows and syneruptive-spouted type lahars associated with phreatic eruptions. Detailed studies of phreatic phenomena are required, as it remains difficult to identify and reconstruct these processes based on the characteristics of the deposits.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121450256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analysis of detritus from mantle-derived rocks","authors":"S. Arai","doi":"10.5575/GEOSOC.2017.0068","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0068","url":null,"abstract":"Detrital materials supplied from mantle-derived rocks have peculiar mechanical and chemical characteristics that make them excellent sedimentological and tectonic markers. Chromian spinels are well known and favored petrogenetic indicators because they contain several important cations, including Mg, Fe, Cr, Al, and Fe, as their main components. The Mg/(Mg + Fe) ratio (= Mg#), Cr/(Cr + Al) ratio (= Cr#), and Ti concentration are important parameters that are commonly analyzed to petrologically characterize chromian spinels. The main hosts in the chromian spinels of mantle peridotites (harzburgite and lherzolite) and their serpentinized equivalents are Mg# and Cr#, which are controlled by the equilibrium temperature (degree of subsolidus cooling) and degree of melt extraction, respectively. The chromian spinels in detritus materials are chemically stable during sedimentation processes, and can thus serve as powerful indicators of the tectonic and geologic history of the hinterland. The derivation of detrital chromian spinels, peridotites (serpentinites), chromitites, or volcanics can be partially identified by analyzing their Mg#, Cr#, and Ti concentrations in combination with their textures. The petrologic character of highly sheared serpentinite, such as the matrix of a serpentinite mélange complex, sometimes yields an inconclusive geodynamic history, but this can potentially be inferred from detrital chromian spinels in nearby sediments. Detrital chromian spinels from modern sediments are also useful for obtaining a general view of large peridotite bodies, such as the mantle section of the Oman ophiolite. When we compare the detrital spinels with those from in situ rocks, we should note that the host rocks containing the detritus material have already been eroded. If we analyze the serpentinite sandstones together with their closely associated peridotite bodies, we can possibly obtain information on the petrologic heterogeneity of the upper mantle. Our petrographic investigation of the Circum-Izu Massif Serpentinite Belt, central Japan, provides a good example of such a combined analysis of these peridotite-serpentinite sandstone pairs.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"117 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128950363","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleoweathering and paleoclimatic condition inferred from paleosol facies in the Miocene Seto Porcelain Clay Formation in the Setouchi Geologic Province, central Japan","authors":"N. Hatano, Kohki Yoshida","doi":"10.5575/GEOSOC.2017.0070","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0070","url":null,"abstract":"Paleosol descriptions and sedimentary facies analysis were performed for the Miocene Seto Porcelain Clay Formation in Toyota City, Aichi Prefecture, to reveal the paleoweathering conditions after deposition. The sedimentary facies analysis suggests that deposition occurred mainly in a lacustrine, backswamp floodplain of a meandering river channel. Three paleosol horizons have been described and compared with modern soils. Histosol-like and inceptisol-like paleosols reflect the local topography and sedimentary features related to drainage conditions, vegetation cover, and sedimentation rate. Conversely, the vertic ultisol-like and ultisol-like paleosols were developed on a gently sloping terrace. The vertic ultisol-like paleosol is characterized by an illuviated clay-rich B horizon (Bt horizon, argillic horizon), pedogenic slickensides, hummock-and-swale microtopography showing gilgai microrelief, and festoon-shaped horizons showing mukkara subsurface structures. Vertic paleosol indicates the typical soil type, suggesting that the climatic conditions in this period were warm and humid with pronounced seasonality.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"96 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129244118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stratigraphy of the Lower Cretaceous Tetori Group and stratigraphic implication of plant assemblages in the border area between Ishikawa and Fukui Prefectures, central Japan","authors":"Y. Sakai, Shinji Sekido, A. Matsuoka","doi":"10.5575/GEOSOC.2017.0074","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0074","url":null,"abstract":"The stratigraphy of the Tetori Group in the Shiramine area of Ishikawa Prefecture and the Takinamigawa area of Fukui Prefecture has been reexamined, and the plant-bearing horizons stratigraphically compared. The Tetori Group in the study areas is divided into the Gomijima, Kuwajima, Akaiwa, and Kitadani Formations, in ascending stratigraphic order. Plant assemblages from the Akaiwa Formation around Mt. Oarashiyama in the Shiramine area comrise 23 species of 18 genera typified by the abundant occurrence of Tetoritype floral elements including ferns, ginkgoaleans, and conifers. The floral elements are associated with minor Zamites-like macrophyllous bennettitalean (or cycadalean) and microphyllous coniferous foliage represented by Brachyphyllum, indicating a climate with a dry season(s). Previously the occurrence of the Ryoseki-type floral elements was presumed to be consistent with floral change and a warming and drying climate during the deposition of the Kitadani Formation. However, this study suggests that such a trend started from the deposition of the Akaiwa Formation, earlier than previously thought.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"18 12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125766125","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleocene diatoms (Bacillariophyta) from the Urahoro area, eastern Hokkaido","authors":"C. Shimada, R. Jenkins, M. Yamasaki, Y. Hikida, Yuichiro Tanaka, K. Amano","doi":"10.5575/GEOSOC.2017.0072","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0072","url":null,"abstract":": Paleocene diatoms are reported from a","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134154349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lecture note on the theories of strain and deformation analyses:: 6. Progressive deformation and kinematic vorticity analysis","authors":"A. Yamaji","doi":"10.5575/GEOSOC.2017.0073","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0073","url":null,"abstract":"地質学的過去におきた歪みや変形の量や方向を,地質学的 に妥当な仮定のもとに,定量的に見積もるのが歪み解析と変 形解析である.この講座の第 1回で述べたように,運動は 並進(重心の移動)と歪み(形態変化)と剛体回転に分けて考え ることができる(山路, 2016a).第 4回と第 5回で扱った Rf/φ歪み解析は,この意味の歪みを推定する方法であった (山路, 2017a, b).歪みと剛体回転の大きさの比を,複数の ポーフィロクラストから推定するのが運動論的渦度解析(kinematic vorticity analysis)であるが,今回は双曲幾何学を 使ってこれを定式化する.運動論的渦度解析に利用できる 種々のデータの説明,方法の詳細と限界については,ほかの 文献(石井, 1996; Passchier and Trouw, 2005, §9; Xypolias, 2010)を参照されたい.小論の特徴は,双曲幾何学に よる定式化で,理論面の見通しがよくなることを示すことに ある.そして特に,ノモン投影の運動論的渦度解析における 有用性を示すことにある. 次節以下,まず,変形の速度が一様と仮定したうえで,累 進変形(e.g., 金川, 2011)の結果どんな変形が達成されるの か,つまり微小歪みと有限歪みの関係を導く.また,有限歪 みの時間変化を検討する.また,双曲幾何(本講座第 4回) との関連性を議論する.そして,それを基礎として運動論的 渦度を導入し,最後に天然のデータからそれを評価する方法 を考える.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123314681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Devonian chert in the Permian Kozuki Formation of the Ultra-Tamba Zone, eastern Okayama Prefecture, Southwest Japan","authors":"S. Takemura, A. Takemura, Hikaru Ueno, Yoshiaki Sugamori, H. Furutani","doi":"10.5575/GEOSOC.2017.0064","DOIUrl":"https://doi.org/10.5575/GEOSOC.2017.0064","url":null,"abstract":"Devonian chert beds in the Permian Kozuki Formation of the Ultra-Tamba Zone are reported from Mimasaka City, Okayama Prefecture, Southwest Japan. The Kozuki Formation consists mainly of Permian clastic rocks and felsic tuffs with basalts, Carboniferous limestone, and Early Permian cherts, and is therefore interpreted as a Permian accretionary complex similar to the other formations of the Ultra-Tamba Zone. The Devonian chert beds are frequently intercalated with black layers composed of magnetite, in which a wellpreserved radiolarian fauna occurs. These magnetite beds with radiolarian shells indicate the sedimentary origin derived from hydrothermal activity on the seafloor. The radiolarian fauna contains Holoeciscus foremanae and H. elongatus, as well as Ceratoikiscum avimexpectans and Archocyrtium sp., indicating the Fammenian Age of Late Devonian. These are the oldest fossils in the Chugoku District and the chert beds represent one of the oldest allochthons within the accretionary complexes of Japan, similar in age to the Devonian chert of the Nedamo Belt in the Tohoku District.","PeriodicalId":264556,"journal":{"name":"Journal of the Geological Society of Japan","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128495071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}