地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
112 巻 , 1 号
選択された号の論文の12件中1~12を表示しています
  • 椛島 太郎, 磯崎 行雄, 平田 岳史, 丸山 茂徳, 君波 和雄, 西村 祐二郎
    2003 年 112 巻 1 号 p. 1-17
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    Zircon U-Pb ages were re-measured for Archean felsic intrusive and volcanic rocks of the greenstone belt in the North Pole area, Pilbara craton, Western Australia by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A concordant age for a single zircon grain from the North Pole adamellite is measured to be 3404 ± 60 Ma, much younger than previously reported zircon U-Pb discordant age 3459 ± 19 Ma from the same unit. Together with the oldest 207 Pb/206 Pb TIMS age 3418.3 ± 0.13 Ma previously reported, the present result suggests that adamellite intruded into the surrounding basaltic greenstones at ca. 3420 Ma.
    We measured 16 zircon grains in total from 4 rhyolitic tuffs intercalated in the greenstones of the area, and most of them range within 3482-3576 Ma. The youngest age, i.e. 3482 Ma, is consistent with the previously reported concordant TIMS age, 3458 Ma, from the same unit. This suggests that rhyolitic volcanism occurred probably around 3460 Ma. A single zircon grain from rhyolite (lava) with an exceptionally older 207Pb/206Pb age, 3609 ± 31 Ma, may have been reworked from older units.
    The present results indicate that the North Pole adamellite intruded into the basaltic greenstones at about 3420 Ma, while rhyolite erupted much earlier at 3458 Ma together with basalt. This newly recognized age gap of ca. 40 m.y. is consistent with the field observations on the intrusion of adamellite into basaltic greenstones, and with the interbedded association of rhyolite and basalt. Thus the previous model for a syngenetic and synchronous relationship between adamellite and rhyolite in the North Pole area is clearly rejected.
  • 太田 陽子, 渡辺 満久, 鈴木 康弘, 澤 祥
    2003 年 112 巻 1 号 p. 18-34
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    A remarkable surface rupture appeared in the 1999 Chichi earthquake, in central Taiwan. The nature and location of the earthquake fault was studied in detail immediately after the earthquake (e.g., Central Geological Survey, Taiwan, 2000). Its location to the pre-existing active fault trace, however, was unknown. We wish to establish a location relationship between the earthquake fault and the pre-existing active faults which are mapped from photo interpretation at a scale of 1 : 20, 000, taken in 1970's, supplemented by field observation. The identified active faults are divided into four types from I to IV, depending on their certainty as active faults as well as their location accuracy. A Type I fault is where the active fault is definite and location is certain, II is also an active fault, but with a little uncertainty as to exact location due to subsequent erosion of the fault sacrp, and also because of sedimentation on the foot-wall, and III is a concealed fault beneath the younger sediment. Type IV appeared as a lineament without any clear evidence of deformed morphology. After mapping these active faults, we added the location of our observation to the 1999 surface rupture and GPS sites for measuring the earthquake fault using CGS map (2000).
    We present eight areas to show the exact relationship between active fault trace and earthquake fault trace and summarized them into Fig. 10. We concluded that most (ca. more than 80%) of the earthquake fault trace occurred exactly on the active fault of Type I and II. The earthqauke fault often appeard even on lineament of Type IV, implying that this lineament should be mapped for the acive fault map. On the young alluvial lowland where it is too young to record past faulting, the earthquake fault still appears on the probable extension of known active fault trace. The earthquake fault sometimes jumps from one fault to another where two or three active fault traces are recognized. Although we can not explain the reason for such a jumping, the earthquake fault still appears on one of the known faults. Therefore, repeated faulting activity during the late Quaternary on the same trace was confirmed for the Chelugmu Fault. This implies the detailed mapping of many other active faults in Taiwan, including Type III and IV, is essential for the understanding of future rupture locations.
  • 鈴木 茂之, 檀原 徹, 田中 元
    2003 年 112 巻 1 号 p. 35-49
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    Seven tuff samples, 5 from the Kibi Group (so-called mountain gravel) and 2 from the Katsuta Group were dated by using the fission-track technique. These samples were collected from the Kibi Plateau area in Okayama Prefecture. Fission-track ages of 34.3 ± 1.8 Ma (Yoshii Formation), 35.8 ± 1.3 Ma and 34.0 ± 2.7 Ma (Tomiyosi Formation), 27.4 ± 1.9 Ma and 27.1 ± 1.5 Ma (Tsudaka Formation) were obtained from the Kibi Group. Until now, the Kibi Group was considered to be deposited during the Quaternary period due to its unconsolidated nature. These dating results indicate that the Kibi Group is of Eocene to Oligocene in age. From the Katsuta Group, fission track ages of 17.9 ± 2.1 Ma (Yoshino Formation) and 16.2 ± 2.1 Ma (Takakura Formation) were obtained. These data agree with microfossil dating.
  • 田林 明, 藤永 豪, 中村 昭史
    2003 年 112 巻 1 号 p. 50-72
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    At present Japanese agriculture is suffering from various problems. One of them is a severe shortage of successors to take over farms, which have been long kept by their parents, who engaged in both farming and off-farm work. They are now retiring. In this situation it is important to discuss the prospects of agricultural activities and rural communities. This study analyzes the characteristics of present agriculture and evaluates the sustainability of agricultural activities in the near future. The study area is the Isawa alluvial fan in Iwate Prefecture where many part-time farmers have just started retiring.
    First, 214 rural villages in the Isawa alluvial fan were classified into three types by applying a multivariate analysis to 1995 Agricultural Census data. The types are agricultural, intermediate, and non-agricultural. The agricultural villages are distributed in the southern part of the alluvial fan, with high diluvial uplands with elevations of 100 to 200 meters that are remote from local urban centers. On the other hand, the non-agricultural villages extend over the northern and eastern part of the fan area with low elevations and are located near local urban centers or along the main roads. The intermediate villages are distributed between the areas of the former two types of village.
    Based on field-work in the sample villages which represent the three types, farmers in the agricultural village have a relatively strong inclination to continue farming and they have organized a farming support group to keep agriculture by themselves. In the non-agricultural village farm size is relatively small, and most farmers' main income sources are off-farm work. They will gradually transfer their agricultural activities to full-time farmers in neighboring villages and retire from farming. In the intermediate village, a few viable farmers will continue as full-time farmers, while many others will retire from farming. The former will gradually take over the agricultural activities of the latter.
    The regional differences of the agriculture types are mainly defined by accessibility to local urban centers and the land conditions such as the elevations of diluvial uplands in the Isawa alluvial fan.
  • 石井 久生
    2003 年 112 巻 1 号 p. 73-94
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    In the Autonomous Community of the Basque Country, situated in northern Spain, the geographical distribution of ethno-linguistic groups is characterized by a clear spatial pattern. This pattern is defined by a bipolar spatial structure. There is one zone with a high concentration of Basque speakers in the northeastern part of the Autonomous Community, extending from Gipuzkoa to central Bizkaia. There is also a zone in which Spanish speakers, dominate which extends from the western to the southern part of the area, from the western part of Bizkaia to all of Alava.
    In recent years, the proportion of Basque speakers has been rising gradually, especially in the contact area of the two geo-linguistic zones, and a remarkable increase in the number of Basque speakers can be observed in the predominantly Spanish speaking zone. This phenomenon cannot be explained simply by the diffusion of ethno-linguistic elements through geographical mobility.
    This recent increase in the number of Basque speakers is correlated with the remarkable spread of new Basque speakers who have recently acquired sufficient competence in the Basque language, although their mother tongue is not Basque. The number of new Basque speakers has sharply increased, especially within the younger generation. This phenomenon is a product of the introduction and the implementation of a bilingual educational system since the 1980s. This means that a program of effective institutional support instituted by the administration is functioning successfully for the revival and the maintenance of the Basque language.
  • 佐藤 大祐
    2003 年 112 巻 1 号 p. 95-113
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    Boating activities in Lake Kasumigaura include not only those for yacht sailing and motor boating, but also for black bass fishing that has rapidly increased since the 1990s. This paper attempts to examine the developing process of pleasure boat storage facilities and boating activities around Lake Kasumigaura.
    Motorboats were mainly used for crucian fishing, duck hunting and cherry blossom viewing in the Suigou area (lower swampy area on the southern lakeside) in the 1910s. When the creeks, which were used as moorings for most of the motorboats, were reclaimed in the process of the farmland development in the 1960s, boat storage facilities were promoted to be opened in this area. On the other hand, sailboats were introduced as an extension of row boats by the graduates of Tsuchiura Junior High School in 1927, and Kasumigaura Yacht Harbor (Keisei Marina) was subsequently built by a railway company in 1966 at Tsuchiura city. The users of these storage facilities consisted mainly of office workers as well as students from Tokyo.
    However, eutrophication occurred owing to the development of agriculture, livestock industry, carp aquiculture and urbanization since the 1960s. Therefore, bathing places of Lake Kasumigaura were closed in 1975. In addition to eutrophication, the development of marinas around Tokyo Bay since the 1980s caused consequently the distribution area of storage facility users (including the Keisei Marina) shrink. Furthermore, catches of fish decreased due to over fishing, desalination and decrease of aquatic plants necessary for spawning grounds. Fishermen, therefore, had no other choice than giving up fishing.
    With the expansion of black bass fishing, storage facilities for black bass fishing boats were opened in late the 1980s and were expanded due to the influx of users from Tokyo. These boat storage facilities consist of only boatyards, maintenance shops and boat ramps. The boat ramps were converted from former naval or industrial facilities. The formation of such simple storage facilities is the main reason that the storage fees are kept to a cheap level, thus the users were mainly consisted of company employees aged 20-30. Owing to the expansion of the social stratum of boat owners, storage facilities like car parking lots were opened inland. The users of the inland facilities transport their boats to ports with their cars. For boating activities concerned, boat fishing areas for black bass were formed in the nearshore area of the lake as fisheries declined.
  • 山野 明男
    2003 年 112 巻 1 号 p. 114-130
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    This research examines the development process of farming conditions of settlers in Hachirogata reclaimed land. The settlers numbered 589 in all. A total of 551 farm at present and 38 have abandoned farming.
    The development process of agriculture on Hachirogata reclaimed land can be divided into 3 periods : the first period -commencement of farming, the second-change in farming, and the third -settlement of farming. The development process of agriculture on Hachirogata reclaimed land (Ogata village) is shown in Fig. 7.
    I analyze why the 551 settlers separated into two farming groups. The results are as follows. 1) One group, 249 mainly from Akita prefecture, controls the production of rice. 2) The native places of the settlers play an important part in their division into two groups. 3) The settlers brought their native village culture into their settlement of reclaimed lands.
  • 日本地学史編纂委員会 , 東京地学協会
    2003 年 112 巻 1 号 p. 131-160
    発行日: 2003/02/25
    公開日: 2010/04/23
    ジャーナル フリー
  • 奥野 充, 岩田 修二, 江口 孝雄, 西村 昭, 小出 良幸
    2003 年 112 巻 1 号 p. 161-168
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 岩森 光
    2003 年 112 巻 1 号 p. 169-170
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 井上 明
    2003 年 112 巻 1 号 p. 171-179
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 白尾 元理
    2003 年 112 巻 1 号 p. Plate1-Plate2
    発行日: 2003/02/25
    公開日: 2009/11/12
    ジャーナル フリー
feedback
Top