著者

大島 章一

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.3, pp.474-482, 2000-06-25 (Released:2010-10-13)

参考文献数

25

著者

岩田 修二

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.106, no.5, pp.752-753, 1997-10-25 (Released:2009-11-12)

被引用文献数

1

著者

長谷川 昭 中島 淳一 北 佐枝子 辻 優介 新居 恭平 岡田 知己 松澤 暢 趙 大鵬

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.117, no.1, pp.59-75, 2008-02-25 (Released:2010-02-10)

参考文献数

50

被引用文献数

5 8

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Transportation of H2O from the slab to the arc crust by way of the mantle wedge is discussed based on seismic observations in the northeastern Japan subduction zone. A belt of intraslab seismicity, perhaps caused by dehydration of eclogite-forming phase transformations, has been found in the Pacific slab crust at depths of 70-90 km parallel to iso-depth contours of the plate interface, showing the major locations of slab dehydration. H2O thus released from the slab may be hosted by serpentine and chlorite just above the slab and is dragged downward. DD seismic tomography detected this layer of serpentine and chlorite as a thin S-wave low-velocity layer. Serpentine and chlorite thus brought down to a depth of 150-200 km should decompose there. H2O released by this dehydration decomposition is then transported upward and encounters the upwelling flow directly above, which perhaps causes partial melting of materials within the upwelling flow. Seismic tomography studies have clearly imaged this upwelling flow as an inclined sheet-like seismic low-velocity zone at depths of 30-150 km in the mantle wedge subparallel to the subducted slab. This upwelling flow finally meets the Moho below the volcanic front, and melts thus transported perhaps stagnate directly below the Moho. Some of them further migrate into the crust, and are also imaged by seismic tomography as low velocity areas. Their upward migration and repeated discharge to the surface form the volcanic front. Seismic tomography study of the mantle wedge further revealed along-arc variations of the inclined low-velocity zone: very low velocity areas appear periodically every ∼80 km along the strike of the arc in the backarc region of northeastern Japan above which clustering of Quaternary volcanoes and topography highs are located, suggesting that melts could segregate from these very low velocity areas in the upwelling flow and rise vertically to form volcanoes at the surface in the backarc region.

著者

府川 宗雄

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.105, no.6, pp.709-717, 1996-12-25 (Released:2009-11-12)

参考文献数

19

被引用文献数

4 4

著者

田切 美智雄 森本 麻希 望月 涼子 横須賀 歩 DUNKLEY Daniel J. 足立 達朗

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.2, pp.245-256, 2010-04-25

参考文献数

29

被引用文献数

8 20

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Hitachi metamorphic rocks located in the southern part of the Abukuma Mountains, Northeast Japan, distinctively contain meta-volcanic rocks and meta/sheared granitoids. The igneous ages of meta-granite and meta-porphyry from the Hitachi metamorphic rocks were determined by the SHRIMP zircon method. In this paper, we describe occurrence, petrography, and petrochemical characteristics of these studied rocks. Meta-porphyry, with an igneous age of 506 Ma, intrudes into the meta-volcanic rocks of the Akazawa Formation of the Hitachi metamorphic rocks and has a micrographic texture and a spherulitic texture of an igneous origin. Previous studies have already reported an igneous age of 491 Ma for meta/sheared granitoids using the SHRIMP zircon method. Cambrian meta/sheared granitoid samples occur widely as a granitic body in the northeastern part of the Hitachi metamorphic rocks. (A) Meta-granite of the same age (498 Ma) as the sample used for the above dating is found as boulders in meta-conglomerates. The meta-conglomerate, which is found in the Daioin Formation of the Hitachi metamorphic rocks, lies unconformably on a Cambrian meta-granite body. Both meta-volcanic rocks and meta/sheared granitoids have chemical characteristics commonly associated with island arc volcanism. As such, the Akazawa Formation is likely to have originated in the Cambrian era, although we have no SHRIMP age for meta-volcanic rocks of the Akazawa Formation.

著者

尾方 隆幸

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.124, no.1, pp.31-41, 2015-02-25 (Released:2015-03-11)

参考文献数

19

被引用文献数

2 5

---

Geoparks target all geoscientific multidisciplinary and interdisciplinary areas, whereas scientific topics of Japanese geoparks incline toward specific themes. Content analysis reveals that many geoparks attach greater importance to solid earth sciences (e.g. geology) and/or human geosciences (e.g. geography) than biogeosciences (e.g. paleontology), atmospheric and hydrospheric sciences (e.g. meteorology), and space and planetary sciences. Specialization coefficients clearly show this inclination, and suggest a shift from geological to geographical themes. Multivariate analyses also indicate several clusters of Japanese geoparks characterized mainly by geological and/or geographical contents. This specialization enumerates geological and/or geographical topics, and restricts a seamless geostory for interpreting a landscape. An educational program on the Ryukyu Islands focuses on various geomorphic processes related to the global environmental system. This program contributes to both an attractive and scientific geostory on interactions among atmosphere, hydrosphere, and geosphere. A seamless geostory using multidisciplinary and interdisciplinary approaches should be given more consideration in all Japanese geoparks, because it enhances a comprehensive outreach and education on geoscience.

著者

松本 良

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.1, pp.7-42, 2009-02-25 (Released:2010-04-05)

参考文献数

94

被引用文献数

14 21

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Gas hydrate, an ice-like solid compound composed of methane and water molecules, was “re-discovered” from ocean sediments in the mid-20th century, while it had been known as a chemical material to chemists and chemical engineers even in the early 19th century. Since the re-discovery of natural gas hydrate it has been attracting growing interest among geoscientists from the viewpoint of potential natural gas resources, possible impact on global environmental changes, and trigger of geo-hazards such as landslides and coastal erosion. The development of gas hydrate science has been marked by a rapid increase of studies in publications from 1991 to 1999, reflecting ODP expeditions to the mid-America Trench and Blake Ridge, where deep corings recovered solid gas hydrate samples. The number of papers in international journals has increased to 500 to 600 annually in the last few years. Recent development of marine geology and geophysics, in particular of the Ocean Drilling Program (ODP), has dramatically increased our knowledge of gas hydrate and related phenomena. Bottom simulating reflector (BSR) on seismic profiles corresponds to the base of the gas hydrate zone in sediments, and is considered to be a useful tool to identify the distribution of marine gas hydrates. The base of gas hydrate stability (BGHS) is determined from P-T conditions of sediments and water depth, and BSR is expected to occur at the depth of BGHS. However, BSR is not always consistent with BGHS; and, in some cases, even two BSRs are identified at around the depth of BGHS. These observations seem to imply that marine gas hydrate is not necessarily stable at the present position but represents ephemeral and transient conditions.  Integrated research activities of scientific projects and industry exploration efforts have identified two types of gas hydrate in marine sediments. These are deep-seated, stratigraphic-type deposits and shallow/structural accumulation. Japan's long-term exploration project led by Ministry of Economy, Trade and Industry (METI) has been targeting the stratigraphic type in the Nankai Trough, where 40 tcf of methane has been estimated to occur as concentrated gas hydrate deposits. Shallow accumulations are usually associated with gas chimney structures, and are common throughout the marginal seas of the western Pacific. Massive accumulation of the shallow type seems to be promising for gas production from gas hydrate as well.  Sudden and major changes to the earth's environment and mass extinctions are characterized by sharp negative excursions of carbon isotopic composition. Massive dissociation of C-13 depleted gas hydrate with δ13C of -40 to -100‰, is believed to have caused such global changes. The Paleocene-Eocene boundary event (PETM event) is the best-explained case of gas hydrate-induced biotic overturn. However, serious problems have recently emerged from considerations of thermal propagation through sediments. A sudden increase of methane concentration at the Last Glacial Maximum has also been considered to result from gas hydrate dissociation, but the response of gas hydrate was not so simple during the Quaternary, when low sea level during glacial periods possibly de-stabilized subsurface gas hydrate, unlike the PETM of ice-free ocean.

著者

川又 基人 菅沼 悠介 土井 浩一郎 澤柿 教伸 服部 晃久

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.129, no.3, pp.315-336, 2020-06-25 (Released:2020-07-11)

参考文献数

69

被引用文献数

2

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The purpose of geomorphological studies in East Antarctica is to understand past fluctuations of the Antarctic Ice Sheet, which is essential to constrain ice sheet models and predict future behavior of the East Antarctic Ice Sheet. Here we show a deglacial history of Skarvsnes, at the southern part of the Soya Coast, East Antarctica based on a geomorphological field survey and newly obtained surface exposure ages. Bedrock higher than ca. 250 m a.s.l. at the northwest part of Skarvsnes (Skjegget) is weathered extensively, whereas bedrock below ca. 250 m a.s.l. is relatively unweathered. The degree of weathering of bedrock above 250 m a.s.l. is similar to that at the northern part of the Soya Coast, which is thought to have been ice-free throughout the last glacial period. Therefore, a clear difference in the degree of weathering depending on altitude probably indicates the lower limit of the ice sheet elevation during the last glacial period at Skarvsnes. Judging from the multiple directions of glacial striae, the ice sheet covering the area retreated while changing flow direction under the influence of the bedrock topography after the last glacial period. Since ca. 9 ka, the ice sheet is thought to have thinned and eventually divided into two major ice streams (northward and southward) that were obstructed by a 362 m a.s.l. mountain (Shirasuso-Yama), at the southeastern part of Skarvsnes. However, the timing of the initiation of the ice sheet retreat and its duration remain unclear. Therefore, additional surface exposure ages from various areas and heights at Skarvsnes are required for a detailed reconstruction of the ice retreat history and to understand its mechanism.

著者

太田 陽子 小田切 聡子

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.103, no.3, pp.243-267, 1994-06-25 (Released:2009-11-12)

参考文献数

40

被引用文献数

4 8

---

1) 土佐佐賀から千尋岬東方にいたる地域の海成段丘を高位から H1, H2, H3, M, Lに分類した。M面およびそれより高位の段丘の形成は氷河性の海面変化に伴っており, M面は最終問氷期最盛期 (約125ka, 酸素同位体ステージ5e) の海進期に形成された。 H2, H1はそれぞれステージ7, および9の間氷期に対応する海進期を示す可能性があるが年代を確定できない。L面はさらに細分され, L1が完新世海進高頂期を, L2以下の面はその後の間欠的隆起を示している。2) 本地域は北西に低下する二つの傾動域 (伊の岬変動区と足摺変動区) に分かれ, それぞれの地域内ではH1面形成期以降の約3°万年間同様式の傾動が続いていた。M面形成期以降の最大平均隆起速度は 0.55m/ka (足摺岬) である。3) 二つの変動区の形成はプレート境界から分岐した断層の活動に由来すると思われる。伊の岬変動区はおそらく伊の岬断層を震源断層として形成されたと推定できるが, 足摺変動区の傾動を説明する震源断層を特定することはできなかった。細分される完新世段丘群はこれらの分岐断層の最近の活動史を記録しており, 上記両変動区で隆起時期を異にしている。

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.7, no.11, pp.615b-616, 1895-11-10 (Released:2010-12-22)

著者

中井 順二 駒沢 正夫 大久保 泰邦

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.96, no.4, pp.185-200, 1987-08-25 (Released:2009-11-12)

参考文献数

15

被引用文献数

2 2

---

Bouguer anomaly map of the Kanto district was compiled. On the whole, gravity anomalies are high in Tsukubasan areas, and low in the central parts of the Kanto plain. Negative anomalies in the Boso peninsula and the Tama hills suggest the basement structures of the sedimentary basins. The Kanto mountains district is bounded on the east by steep gradient of gravity anomaly. The above gravity features can be recognized in the map of the upward continuation. The gravity trend along Narashino, Sakura and Omigawa is more clearly indicated in the map of the first derivative, and the tectonic line covered by sediments can be supposed.In the Izu peninsula and the Tanzawa mountains district, gravity anomalies are rather high and low anomaly zone is recognized between these two areas. The northern border part of this zone correspond to Kannawa fault and Kozu-Matuda fault.Aeromagnetic map was compiled with the data obtained by New Energy Development Organization and Geological Survey of Japan.Generally, the Kanto district is surrounded by intense magnetic anomalies with short wavelength which are distributed along Nasu volcanic zone and Fuji volcanic zone.In the central part of the Kanto plain, weak magnetic anomalies are scattered zonally in the E-W direction. According to the geological and well data, this zone seems to be corresponded to Sambagawa metamorphic belt and these anomalies are presumably caused by the basic or ultrabasic rocks.The Hakone mountains district has sharp anomalies with short wavelengths, and the maximum amplitude of the anomalies reachs 900nT. Low anomaly zones are recognized arround this high anomalies. The source of this low anomalies is not clear, but it is of great interest geologically and geophysically.

著者

中西 僚太郎

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.124, no.6, pp.917-936, 2015-12-25 (Released:2016-01-27)

参考文献数

32

被引用文献数

2 2

---

This study surveys pictures of Mt. Fuji in the following three categories: Japanese paintings, pictorial mountain-climbing guide maps, and panoramic maps. To date, art historians have conducted many studies on pictures of Mt. Fuji. However, there have been no studies that consider pictorial mountain-climbing guide maps and panoramic maps as “pictures” of the mountain. Certainly, this study's major contribution to research on Mt. Fuji is its comprehensive understanding of “picture.” More importantly, the fact that most art historians have ignored panoramic maps drawn by Yoshida Hatsusaburo, Kaneko Jyoko, and others in the first half of the twentieth century is a mistake. They did examine Ukiyoe prints by Katsushika Hokusai, Utagawa Hiroshige, and others from the nineteenth century; nevertheless, both these Ukiyoe prints and the panoramic maps drawn by Yoshida Hatsusaburo were forms of commercial art. Geographers dealt with panoramic maps, which have been examined by other geographers and map enthusiasts. From a geographical perspective, Mt. Fuji drawn as a panoramic map is a valuable research resource. In addition, by examining Japanese paintings and pictorial mountain-climbing guide maps, Mt. Fuji is recognized to be an awe-inspiring subject, as well as the one that can be revered. Furthermore, by examining of panoramic maps, it is demonstrated that Mt. Fuji was recognized to be an object of modern tourism.

著者

荒牧 重雄

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.95, no.7, pp.489-495, 1987-01-25 (Released:2009-11-12)

参考文献数

20

著者

丸山 茂徳 大森 聡一 千秋 博紀 河合 研志 B.F. WINDLEY

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.1, pp.115-223, 2011-02-25 (Released:2011-05-20)

参考文献数

217

被引用文献数

26 42 22

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Pacific-type orogeny (PTO) has long been recognized as a contrasting accretionary alternative to continent-continent collisional orogeny. However, since the original concept was proposed, there have many new developments, which make it timely to produce a new re-evaluated model, in which we emphasize the following new aspects. First, substantial growth of Tonarite–Trondhjemite–Granite (TTG) crust, and second the reductive effect of tectonic erosion. The modern analog of a Pacific-type orogen developed through six stages of growth exemplified by specific regions; initial stage 1: the southern end of the Andes; stage 2: exhumation to the mid-crustal level at Indonesia outer arc; stage 3: the Barrovian hydration stage at Kii Peninsula, SW Japan; stage 4: the initial stage of surface exposure of the high-P/T regional metamorphic belt at Olympic Peninsula, south of Seattle, USA; stage 5: exposure of the orogenic core at the surface at the Shimanto metamorphic belt, SW Japan; and stage 6: post-orogenic processes including tectonic erosion at the Mariana and Japan trench and the Nankai trough. The fundamental framework of a Pacific-type orogen is an accretionary complex, which includes limited ocean floor material, much terrigenous trench sediment, plus island arc, oceanic plateau, and intra-oceanic basaltic material from the ocean. The classic concept of a PTO stresses the importance of the addition within accreted rocks of new subduction-generated arcs and TTGs, which were added along the continental margins particularly during the Cretaceous. Besides the above additional or positive aspects of a PTO, here we emphasize the negative effects of previously little-considered tectonic erosion caused by subduction over time. The evaluation of such extensive tectonic erosion leads a prospect of the presence of huge quantities of TTG material in the lower transition zone, where many subducted slabs have ponded, as illustrated by mantle tomography. This is confirmed by density profiles of the mantle, which show that TTGs are abundant only along the bottom of the upper mantle accompanied by slab peridotite, lherzolite, and MORB. The major velocity anomaly in the lower transition zone is best explained by the predominance of SiO2 phases, hence TTG, and not by MORB or ultramafic rocks. Reasonable calculations indicate that at a depth range of 520-660 km TTG material amounts to 6-7 times more than the total mass of the surface continental crust. The traditional view is that the Japanese islands evolved since 520 Ma through five Pacific-type orogenies, which grew oceanward, thus creating a continuous accretionary complex ca. 400-500 km wide, with TTG growth at the continental side of each orogen. However, the subducting oceanic lithosphere has produced five times more TTG crust compared with the present TTG crust in the Japan islands. This is explained by the fact that over time tectonic erosion has dominated the increasing arc-TTG crust. Accordingly, Japan has lost four arc-TTG crusts to tectonic erosion. TTG material, such as trench sediment, arc crust, and continental margin crust, was fragmented by tectonic erosion and transported into the bottom of the upper mantle at depths of 520-660 km. Worldwide data suggest that tectonic erosion destroyed and fragmented most of the Pacific-type orogens.(View PDF for the rest of the abstract.)

著者

跡部 治

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.84, no.1, pp.41-45, 1975-02-28 (Released:2009-11-12)

著者

鈴木 ドロータ 高木 秀雄 河本 和朗 中村 祐治 中村 れいら

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.124, no.4, pp.587-605, 2015-08-25 (Released:2015-09-17)

参考文献数

23

被引用文献数

1

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本州弧に対する伊豆–ボニン弧への中新世の衝突の影響を受けて,中央構造線の東西走向が,紀伊半島東部伊勢地域で東方に向かって東北東–西南西へと曲がりはじめるものとされている。しかしながら,伊勢地域では第四系堆積物が広く覆っており,都市化も進んでいることから,中央構造線の地表トレースの正確な位置は不明瞭である。中央構造線の位置の正確な把握は,たとえば地盤の違いを反映した地震動予測に資することや,中部日本における中央構造線の折れ曲がりのより正確な説明を与える上でも重要である。本論は伊勢地域(玉城町・伊勢市)に存在する(1)美和ロック玉城工場,(2)伊勢市役所,(3)伊勢観光文化会館のボーリングコアの岩石学的検討を行うとともに,伊勢市内のその他の建設基盤調査資料や,玉城町大池の断層岩類,領家帯に分布すると考えられる宮川沿いの中新統礫岩,伊勢市内に存在する三波川結晶片岩の露頭など,限られた露頭の地質調査結果から,中央構造線の位置をより正確に求めることができた。今回の調査で,三波川変成岩が一部に露出している伊勢神宮外宮に存在する中央構造線が正宮付近に想定され,ジオツーリズムとリンクしたその教育的活用が望まれる。

著者

木村 純一 宮崎 隆 常 青 バグラロフ ・ボグダン 仙田 量子

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.126, no.2, pp.163-179, 2017-04-25 (Released:2017-06-12)

参考文献数

71

被引用文献数

4 4

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The source mantle of the ocean crust on the Pacific Plate is examined using Pb–Nd–Hf isotopes and compared to a global isotope database of ocean basalts. The entire eastern half of the Pacific Plate, formed from an isotopically distinct Pacific mantle along the East Pacific Rise and the Juan de Fuca Ridge, largely remains on the seafloor. Conversely, the western half of the Pacific Plate becomes younger westward and is thought to have formed from the Izanagi–Pacific Ridge (IPR). The ridge subducted along the Kurile–Japan–Nankai–Ryukyu (KJNR) Trench at 70-65 Ma and currently forms the leading edge of the Pacific Plate stagnated in the mantle transition zone beneath China. The subducted IP formed from both Pacific and Indian mantles. Isotopic compositions of the basalts from borehole cores of 165-130 Ma in the western Pacific show that these are of Pacific mantle origin. However, the scraped-off ocean floor basalts (80-70 Ma) in the accretionary prism along the KJNR Trench have Indian mantle signatures. This indicates: (1) the younger western Pacific Plate of IPR origin formed from the Indian mantle, (2) the Indian–Pacific mantle boundary has been stationary in the western Pacific at least since the Cretaceous, and (3) the IPR moved over the boundary. The Indian mantle is thought to have formed from a depleted MORB source mantle (DMM) due to an ancient melt depletion event (2-3 Ga) and subsequent isotopic growth and mixing with a sub-continental lithospheric mantle. In contrast, the Pacific mantle originated from a primitive mantle at 3-1.5 Ga followed by isotopic growth alone. These different formation processes may relate to the formation of the supercontinent and superocean where the Indian mantle was formed in a sub-continental environment whereas the Pacific mantle formed in an oceanic ridge environment.

著者

榎本 隆充

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.112, no.3, pp.453-457, 2003-06-25 (Released:2009-11-12)

著者

青山 千春 鈴木 麻希 松本 良

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.1, pp.vi-vi, 2009-02-25 (Released:2010-04-05)

被引用文献数

1 1

著者

河村 公隆

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.98, no.6, pp.791-797, 1989-12-05 (Released:2009-11-12)

参考文献数

35