Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.118.340
Toshikazu Shinya, Kazuhiro Tanaka
Mud volcanoes are structures formed as a result of the emissions on a land surface or the sea floor of argillaceous material, which is composed of erupting remobilized mud, petroliferous or magmatic gases, and high-salinity water. Recently, large constructions have been planned deep underground besed on the expectation of geological stability. Therefore, it is important to study the origin of erupted mud and groundwater and the depths from which they ascend when evaluating long-term stability. Three active mud volcanoes and a passive mud volcano are found in the Tertiary Shiiya Formation distributed in Tokamachi City, southern part of Niigata Prefecture. Detailed descriptions of the mud volcanoes are provided by Shinya and Tanaka (2005). However, the origin of erupted mud and the formation mechanism of abnormal pore water pressure have not yet been identified. The authors measured the oxygen and hydrogen isotopic ratio of groundwater and vitrinite reflectance of coal fragments separated from erupted mud of an active mud volcano to investigate the origin of erupted mud, particularly the depth of the origin, and the formation mechanism of abnormal pore water pressure. As a result, δ18O and δD values of erupted water are 1.2‰, -5‰ respectively, showing good agreement with those of the Nanatani Formation distributed at a depth of 3400 m in depth in the studied area. Vitrinite reflectance (Ro) shows a bimodal distribution (i.e., 0.3-1.2% and 1.5-1.8%). Ro value of coal fragments sampled from the Shiiya Formation at the outcrop in the studied area are 0.3-0.45%. High Ro (1.5-1.8%) values of coal fragments are obtained in core samples at a depth of 4000 m in the Gimyo SK-1 oil well, which was excavated 2 km NW from the mud volcano. As a result of an investigation of erupted materials at the mud volcano, they were found to have originated at depths of from 3400 m to 4000 m in the studied area. Geothermal temperature of underground at depth of 3400 m to 4000 m in the in the studied area is estimated to be about 120°C to 150°C. Estimated temperature is high enough to cause diagenetic transition from smectite to illite. Transition from smectite to illite results in the release of a large volume of pore water into the sediment. It is concluded that dehydration due to mineral transition might be the major reason for abnormal pore water pressure formation at depths of 3500 m to 4000 m in the study area.
{"title":"Origin of Materials Erupting from Mud Volcano in Tokamachi City, Niigata Prefecture, Central Japan","authors":"Toshikazu Shinya, Kazuhiro Tanaka","doi":"10.5026/JGEOGRAPHY.118.340","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.340","url":null,"abstract":"Mud volcanoes are structures formed as a result of the emissions on a land surface or the sea floor of argillaceous material, which is composed of erupting remobilized mud, petroliferous or magmatic gases, and high-salinity water. Recently, large constructions have been planned deep underground besed on the expectation of geological stability. Therefore, it is important to study the origin of erupted mud and groundwater and the depths from which they ascend when evaluating long-term stability. Three active mud volcanoes and a passive mud volcano are found in the Tertiary Shiiya Formation distributed in Tokamachi City, southern part of Niigata Prefecture. Detailed descriptions of the mud volcanoes are provided by Shinya and Tanaka (2005). However, the origin of erupted mud and the formation mechanism of abnormal pore water pressure have not yet been identified. The authors measured the oxygen and hydrogen isotopic ratio of groundwater and vitrinite reflectance of coal fragments separated from erupted mud of an active mud volcano to investigate the origin of erupted mud, particularly the depth of the origin, and the formation mechanism of abnormal pore water pressure. As a result, δ18O and δD values of erupted water are 1.2‰, -5‰ respectively, showing good agreement with those of the Nanatani Formation distributed at a depth of 3400 m in depth in the studied area. Vitrinite reflectance (Ro) shows a bimodal distribution (i.e., 0.3-1.2% and 1.5-1.8%). Ro value of coal fragments sampled from the Shiiya Formation at the outcrop in the studied area are 0.3-0.45%. High Ro (1.5-1.8%) values of coal fragments are obtained in core samples at a depth of 4000 m in the Gimyo SK-1 oil well, which was excavated 2 km NW from the mud volcano. As a result of an investigation of erupted materials at the mud volcano, they were found to have originated at depths of from 3400 m to 4000 m in the studied area. Geothermal temperature of underground at depth of 3400 m to 4000 m in the in the studied area is estimated to be about 120°C to 150°C. Estimated temperature is high enough to cause diagenetic transition from smectite to illite. Transition from smectite to illite results in the release of a large volume of pore water into the sediment. It is concluded that dehydration due to mineral transition might be the major reason for abnormal pore water pressure formation at depths of 3500 m to 4000 m in the study area.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128870573","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.117.370
Hiromasa Watanabe, Y. Murayama, K. Fujita
Enormous amounts of statistics have been published since the start of the Japanese modern era. Among all of these statistics, modern statistics published in the Meiji era are fundamental for grasping the historical geography of Japan. GIS can be powerful analytical tool for applying such modern statistics to historical regional analyses. Although GIS has potential for historical regional analyses using modern Japanese statistics, studies are not making significant progress at the present time. A background factor is that municipal polygon data and digitized statistics in the Japanese modern era are not available to the public. As a result, in 2004, the authors established the open web-based database titled “Historical regional statistics,” which contains a variety of municipal polygon data and digitized statistics from the modern era. The purpose of this study is to review some digitized statistics and municipal polygon data contained in “Historical regional statistics,” and discus their availability through a case study. “Historical regional statistics” contains eight groups of statistics (39 statistics) and four groups of municipal maps (213 maps). Among these data, military statistics, “Meiji 24 Nen Chohatsu Bukken Ichiranhyo (Requisition Order List in 1891)”, “Fuken Tokei Hyo (Prefectural Statistics)” and “Consolidation of municipalities database” are available and provide versatility. The case study, which analyzes the regional structure of central Japan in the mid-Meiji era, applies the 1890 “Consolidation of municipalities database” and military statistics, “Meiji 24 nen Chohatsu Bukken Ichiranhyo (Requisition order list in 1891)”. Factor and cluster analyses are applied to explain the regional structure. In the factor analysis, eight factors are abstracted from 35 variables. Then, by applying the cluster analysis to the factor matrix, central Japan is classified into six regional types. Complicated research processes for handling or building of data are reduced by digitized statistics and municipal polygons. The regional structure analyzed in the case study can be understood from existing findings of historical geography in Japan. These points show the possible availability of “Historical regional statistics” for historical regional analyses with GIS. On the other hand, it is shown that data used in the case study contain some errors. This point is common to other data in “Historical regional statistics,” and needs to be corrected with the user's cooperation.
自日本近代以来，大量的统计数据被公布出来。在这些统计中，明治时代出版的近代统计是掌握日本历史地理的基础。地理信息系统是将现代统计应用于历史区域分析的有力分析工具。虽然地理信息系统具有利用现代日本统计进行历史区域分析的潜力，但目前的研究尚未取得重大进展。一个背景因素是，日本近代的市政多边形数据和数字化统计无法向公众开放。因此，在2004年，作者建立了一个名为“历史区域统计”的开放式网络数据库，其中包含了各种城市多边形数据和现代数字化统计数据。本研究的目的是回顾“历史区域统计”中包含的一些数字化统计和市政多边形数据，并通过案例研究讨论它们的可用性。《历史区域统计》包含8组统计(39幅)和4组市域图(213幅)。在这些资料中，有军事统计资料、《明治24年征令表》、《县统计》、《市府合并数据库》等，具有通用性。本个案研究运用1890年“市县合并数据库”及军事统计资料《明治24 nen Chohatsu Bukken Ichiranhyo(1891年征用令清单)》，分析明治中期日本中部地区的地域结构。运用因子分析和聚类分析对区域结构进行了解释。在因子分析中，从35个变量中提炼出8个因子。然后，通过对因子矩阵的聚类分析，将日本中部地区划分为6个区域类型。数字化统计和市政多边形减少了处理或构建数据的复杂研究过程。案例分析的区域结构可以从日本历史地理学已有的研究成果中得到理解。这些点显示了利用GIS进行历史区域分析的“历史区域统计”的可能可用性。另一方面，案例研究中使用的数据也存在一定的误差。这一点与“历史区域统计”中的其他数据相同，需要用户配合进行修正。
{"title":"Development of “Historical Regional Statistics” and Utilization of the Data","authors":"Hiromasa Watanabe, Y. Murayama, K. Fujita","doi":"10.5026/JGEOGRAPHY.117.370","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.117.370","url":null,"abstract":"Enormous amounts of statistics have been published since the start of the Japanese modern era. Among all of these statistics, modern statistics published in the Meiji era are fundamental for grasping the historical geography of Japan. GIS can be powerful analytical tool for applying such modern statistics to historical regional analyses. Although GIS has potential for historical regional analyses using modern Japanese statistics, studies are not making significant progress at the present time. A background factor is that municipal polygon data and digitized statistics in the Japanese modern era are not available to the public. As a result, in 2004, the authors established the open web-based database titled “Historical regional statistics,” which contains a variety of municipal polygon data and digitized statistics from the modern era. The purpose of this study is to review some digitized statistics and municipal polygon data contained in “Historical regional statistics,” and discus their availability through a case study. “Historical regional statistics” contains eight groups of statistics (39 statistics) and four groups of municipal maps (213 maps). Among these data, military statistics, “Meiji 24 Nen Chohatsu Bukken Ichiranhyo (Requisition Order List in 1891)”, “Fuken Tokei Hyo (Prefectural Statistics)” and “Consolidation of municipalities database” are available and provide versatility. The case study, which analyzes the regional structure of central Japan in the mid-Meiji era, applies the 1890 “Consolidation of municipalities database” and military statistics, “Meiji 24 nen Chohatsu Bukken Ichiranhyo (Requisition order list in 1891)”. Factor and cluster analyses are applied to explain the regional structure. In the factor analysis, eight factors are abstracted from 35 variables. Then, by applying the cluster analysis to the factor matrix, central Japan is classified into six regional types. Complicated research processes for handling or building of data are reduced by digitized statistics and municipal polygons. The regional structure analyzed in the case study can be understood from existing findings of historical geography in Japan. These points show the possible availability of “Historical regional statistics” for historical regional analyses with GIS. On the other hand, it is shown that data used in the case study contain some errors. This point is common to other data in “Historical regional statistics,” and needs to be corrected with the user's cooperation.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128528457","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.118.986
H. Machiyama, M. Kinoshita, R. Takeuchi, R. Matsumoto, M. Yamano, H. Hamamoto, M. Hiromatsu, M. Satoh, J. Komatsubara
Methane seep activity around the Joetsu Gas Hydrate Field of the western Joetsu Basin, eastern margin of the Japan Sea, was investigated in detail using heat flow measurements. Heat flow was obtained by Ewing-type heat flow probe and SAHF probe with five thermistors at 11-cm intervals using a ROV during nine research cruises in 2004-2008. Average heat flow value obtained on a normal muddy seafloor in this area is 98 ± 13 mW/m2, which is consistent with the ambient heat flow in the Japan Sea. Based on the results of three day's monitoring, temperature fluctuations (> 0.02 K) of bottom water influence sub-bottom temperature at around a depth of 20 cm. Heat flow values greater than 300 mW/m2 were measured not only at the methane venting sites but also in the some areas covered by bacterial mats. This high heat flow value (> 150 mW/m2) is confined to certain areas (several meters to a few tens of meters scale) on the mounds in the Umitaka Spur and the Joetsu Knoll. Therefore, methane migration from the deep subsurface to seafloor occurs on a very local scale, although seismic profiles show the presence of many small faults through gas chimneys just below the mounds. Convex temperature profiles around the gas venting sites indicate the presence of fluid discharges with Darcy's flow velocity of 1.3 × 10-6 m/s and 5.0∼8.6 × 10-7 m/s, respectively. On the other hand, concave temperature profiles, obtained in the “collapsed hydrate zone” on the mounds, may indicate the presence of a recharge zone. Some temperature reversal profiles in areas covered by bacterial mats were probably caused by a lateral fluid movement from a fluid conduit or by the presence of a methane fluid pool. Some apparent negative geothermal gradient anomalies were obtained only in the “collapsed hydrate zone”. Most of these apparent negative anomalies are possibly explained by the influence of bottom water temperature fluctuations. There seem to be some different hydrological regimes in the high methane flux area of the Joetsu Gas Hydrate Field.
{"title":"Heat Flow Distribution around the Joetsu Gas Hydrate Field, Western Joetsu Basin, Eastern Margin of the Japan Sea","authors":"H. Machiyama, M. Kinoshita, R. Takeuchi, R. Matsumoto, M. Yamano, H. Hamamoto, M. Hiromatsu, M. Satoh, J. Komatsubara","doi":"10.5026/JGEOGRAPHY.118.986","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.986","url":null,"abstract":"Methane seep activity around the Joetsu Gas Hydrate Field of the western Joetsu Basin, eastern margin of the Japan Sea, was investigated in detail using heat flow measurements. Heat flow was obtained by Ewing-type heat flow probe and SAHF probe with five thermistors at 11-cm intervals using a ROV during nine research cruises in 2004-2008. Average heat flow value obtained on a normal muddy seafloor in this area is 98 ± 13 mW/m2, which is consistent with the ambient heat flow in the Japan Sea. Based on the results of three day's monitoring, temperature fluctuations (> 0.02 K) of bottom water influence sub-bottom temperature at around a depth of 20 cm. Heat flow values greater than 300 mW/m2 were measured not only at the methane venting sites but also in the some areas covered by bacterial mats. This high heat flow value (> 150 mW/m2) is confined to certain areas (several meters to a few tens of meters scale) on the mounds in the Umitaka Spur and the Joetsu Knoll. Therefore, methane migration from the deep subsurface to seafloor occurs on a very local scale, although seismic profiles show the presence of many small faults through gas chimneys just below the mounds. Convex temperature profiles around the gas venting sites indicate the presence of fluid discharges with Darcy's flow velocity of 1.3 × 10-6 m/s and 5.0∼8.6 × 10-7 m/s, respectively. On the other hand, concave temperature profiles, obtained in the “collapsed hydrate zone” on the mounds, may indicate the presence of a recharge zone. Some temperature reversal profiles in areas covered by bacterial mats were probably caused by a lateral fluid movement from a fluid conduit or by the presence of a methane fluid pool. Some apparent negative geothermal gradient anomalies were obtained only in the “collapsed hydrate zone”. Most of these apparent negative anomalies are possibly explained by the influence of bottom water temperature fluctuations. There seem to be some different hydrological regimes in the high methane flux area of the Joetsu Gas Hydrate Field.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"137 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127494929","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.117.553
S. Kimura, M. Okazaki
To optimize the reactive nitrogen cycle in an ecosystem, technologies to increase nitrogen use efficiency and reduce emissions of nitrogen must be developed. In a watershed-ecosystem, land uses with purification abilities can be a powerful tool to mitigate nitrogen loads from nonpoint sources. This study analyzes the influence of land use on nitrate concentration in the watershed of the Tama River, a typical urban river in Japan. The upstream area is occupied by forest, while the downstream area is dominated by urban land use. In the Tama River watershed, 59% of the total land use is forest ; 23% is urban area ; and, only 5% is occupied by agricultural land. Urban areas are distributed downstream from the middle reaches. The average nitrate nitrogen (NO3--N) concentration in 2004 increased from upstream to downstream: it was 0.7 mg N L-1 in the upstream area, while it rose to 6.0 mg NO3--N L-1 in the downstream area. The river water NO3--N concentration showed a positive correlation with the proportion of urban land use, while it showed a negative correlation with the proportion of forest. However, some small sub-watersheds have low values for NO3--N concentration despite highly urbanized land use. These sub-watersheds are characterized by higher proportions of paddy rice fields to the total area, ranging from 0.3 to 3.0%, and higher proportions of water body areas, ranging from 8.3 to 30.6%, compared to other sub-watersheds. This might indicate the purification ability of the water bodies and paddy rice fields. Land use within 0 to 50 m from the river water surface influenced water quality and forest and other water bodies reduced nitrate concentration. Construction of artificial wetlands or riparian forests would decrease the N load into the river.
{"title":"Relation between Land Use and River Water Quality of the Tama River Watershed","authors":"S. Kimura, M. Okazaki","doi":"10.5026/JGEOGRAPHY.117.553","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.117.553","url":null,"abstract":"To optimize the reactive nitrogen cycle in an ecosystem, technologies to increase nitrogen use efficiency and reduce emissions of nitrogen must be developed. In a watershed-ecosystem, land uses with purification abilities can be a powerful tool to mitigate nitrogen loads from nonpoint sources. This study analyzes the influence of land use on nitrate concentration in the watershed of the Tama River, a typical urban river in Japan. The upstream area is occupied by forest, while the downstream area is dominated by urban land use. In the Tama River watershed, 59% of the total land use is forest ; 23% is urban area ; and, only 5% is occupied by agricultural land. Urban areas are distributed downstream from the middle reaches. The average nitrate nitrogen (NO3--N) concentration in 2004 increased from upstream to downstream: it was 0.7 mg N L-1 in the upstream area, while it rose to 6.0 mg NO3--N L-1 in the downstream area. The river water NO3--N concentration showed a positive correlation with the proportion of urban land use, while it showed a negative correlation with the proportion of forest. However, some small sub-watersheds have low values for NO3--N concentration despite highly urbanized land use. These sub-watersheds are characterized by higher proportions of paddy rice fields to the total area, ranging from 0.3 to 3.0%, and higher proportions of water body areas, ranging from 8.3 to 30.6%, compared to other sub-watersheds. This might indicate the purification ability of the water bodies and paddy rice fields. Land use within 0 to 50 m from the river water surface influenced water quality and forest and other water bodies reduced nitrate concentration. Construction of artificial wetlands or riparian forests would decrease the N load into the river.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126185365","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.119.392
S. Arai
Various characteristics of podiform chromitites, an enigmatic mantle rock member, are reviewed in this article. Chromitites are composed of chromian spinel, with the general formula (Mg, Fe2+)(Cr, Al, Fe3+)2O4, and silicates (mainly olivine). The Fe3+ content is generally very low, being less than 0.1 to all trivalent cations, in mantle chromian spinels. The Mg/(Mg + Fe2+) ratio (= Mg#) changes inversely with the Cr/(Cr + Al) ratio (= Cr#), which increases with an increase of degree of partial melting of mantle peridotites. The Cr# of chromian spinel is generally higher than 0.4 (generally 0.6 to 0.8) in podiform chromitites, varying widely from 0.1 to 0.9 in the mantle peridotite. The podiform chromitite forms pod-like bodies (dimensions of up to 1.5 km × 150 m for an individual pod) with a dunite envelope, totally set within mantle harzburgite. In well-preserved ophiolites, they occur in the uppermost mantle, especially in and beneath the Moho transition zone, which is dominated by dunite. The Cr# of chromian spinel is relatively low (0.4 to 0.6) around the Moho transition zone, and high (>0.6) at deeper levels in the mantle section. Chromitites are denser and less anisotropic in Vp than peridotites, and the Vp is 8.5 to 9 km/sec depending on the proportion of chromian spinel, and higher in the former than in the latter. The podiform chromitite has been interpreted to be one of melt/rock interaction products within the uppermost mantle harzburgite; hybridization of relatively Si-rich melt formed by the breakdown of orthopyroxenes of the wall harzburgite and subsequently supplied primitive melt cause oversaturation in chromian spinel, giving rise to formation of chromitite with a dunite envelope. The fractionated melt leaving high-Cr# podiform chromitite is possibly of arc-magma affinity. Chromitites with low-Cr# (0.4 to 0.6) chromian spinel can be in equilibrium with MORB. Recently found ultra-high pressure minerals, such as diamond, moissanite, Fe-silicides and Ni-Fe-Cr-C alloys, within chromian spinel of podiform chromitites make the genetical history of chromitites highly enigmatic. A new story, which incorporates the genesis and involvement of these highly reducing, ultra-high pressure minerals, is required.
{"title":"Chromitites: An Enigmatic Mantle Rock Type","authors":"S. Arai","doi":"10.5026/JGEOGRAPHY.119.392","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.119.392","url":null,"abstract":"Various characteristics of podiform chromitites, an enigmatic mantle rock member, are reviewed in this article. Chromitites are composed of chromian spinel, with the general formula (Mg, Fe2+)(Cr, Al, Fe3+)2O4, and silicates (mainly olivine). The Fe3+ content is generally very low, being less than 0.1 to all trivalent cations, in mantle chromian spinels. The Mg/(Mg + Fe2+) ratio (= Mg#) changes inversely with the Cr/(Cr + Al) ratio (= Cr#), which increases with an increase of degree of partial melting of mantle peridotites. The Cr# of chromian spinel is generally higher than 0.4 (generally 0.6 to 0.8) in podiform chromitites, varying widely from 0.1 to 0.9 in the mantle peridotite. The podiform chromitite forms pod-like bodies (dimensions of up to 1.5 km × 150 m for an individual pod) with a dunite envelope, totally set within mantle harzburgite. In well-preserved ophiolites, they occur in the uppermost mantle, especially in and beneath the Moho transition zone, which is dominated by dunite. The Cr# of chromian spinel is relatively low (0.4 to 0.6) around the Moho transition zone, and high (>0.6) at deeper levels in the mantle section. Chromitites are denser and less anisotropic in Vp than peridotites, and the Vp is 8.5 to 9 km/sec depending on the proportion of chromian spinel, and higher in the former than in the latter. The podiform chromitite has been interpreted to be one of melt/rock interaction products within the uppermost mantle harzburgite; hybridization of relatively Si-rich melt formed by the breakdown of orthopyroxenes of the wall harzburgite and subsequently supplied primitive melt cause oversaturation in chromian spinel, giving rise to formation of chromitite with a dunite envelope. The fractionated melt leaving high-Cr# podiform chromitite is possibly of arc-magma affinity. Chromitites with low-Cr# (0.4 to 0.6) chromian spinel can be in equilibrium with MORB. Recently found ultra-high pressure minerals, such as diamond, moissanite, Fe-silicides and Ni-Fe-Cr-C alloys, within chromian spinel of podiform chromitites make the genetical history of chromitites highly enigmatic. A new story, which incorporates the genesis and involvement of these highly reducing, ultra-high pressure minerals, is required.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130068008","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.118.1131
Katsuhiko Suzuki, Kentaro Nakamura, Shingo Kato, A. Yamagishi
High-pressure and high-temperature hydrothermal experiments were initially conducted to measure mineral solubility and growth rate. Since then, considerable efforts have been made to characterize the alteration assemblages produced by a wide variety of hydrothermal fluids in different rock types. Based on such information, the conditions of sub-sea floor hydrothermal systems and the formation processes of ore deposits were investigated. These studies significantly depended on many important experimental results obtained by a batch (closed)-type experimental system which gives equilibrium conditions. On the other hand, attention has been also paid to a flow-type experimental system, because natural systems can not only constrained by experiments under equilibrium conditions but, more importantly, by non-equilibrium experiments. Recently, hydrothermal experiments were carried out to better understand interactions among rocks, hydrothermal fluids, and microbes. It has been suggested that microbial ecosystems might be widely distributed within oceanic crusts and be sustained by chemical energy derived from water-rock interactions. However, little is known about the flux of energy and materials involved in microbial activity within the crustal aquifer because of technical difficulties in accessing sub-seafloor environments. A flow-type cultivation system simulating natural hydrothermal environments including crustal aquifers could provide insights into the ecological significance of microorganisms and their contribution to the biogeochemical cycle in global oceans and crusts.
{"title":"Experimental Approach to Obtain a Comprehensive Understanding of the Biogeochemistry of a Seafloor Hydrothermal System","authors":"Katsuhiko Suzuki, Kentaro Nakamura, Shingo Kato, A. Yamagishi","doi":"10.5026/JGEOGRAPHY.118.1131","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.1131","url":null,"abstract":"High-pressure and high-temperature hydrothermal experiments were initially conducted to measure mineral solubility and growth rate. Since then, considerable efforts have been made to characterize the alteration assemblages produced by a wide variety of hydrothermal fluids in different rock types. Based on such information, the conditions of sub-sea floor hydrothermal systems and the formation processes of ore deposits were investigated. These studies significantly depended on many important experimental results obtained by a batch (closed)-type experimental system which gives equilibrium conditions. On the other hand, attention has been also paid to a flow-type experimental system, because natural systems can not only constrained by experiments under equilibrium conditions but, more importantly, by non-equilibrium experiments. Recently, hydrothermal experiments were carried out to better understand interactions among rocks, hydrothermal fluids, and microbes. It has been suggested that microbial ecosystems might be widely distributed within oceanic crusts and be sustained by chemical energy derived from water-rock interactions. However, little is known about the flux of energy and materials involved in microbial activity within the crustal aquifer because of technical difficulties in accessing sub-seafloor environments. A flow-type cultivation system simulating natural hydrothermal environments including crustal aquifers could provide insights into the ecological significance of microorganisms and their contribution to the biogeochemical cycle in global oceans and crusts.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128644070","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.117.124
Hiroshi P. Sato, H. Kumagai, N. Neo, Kentaro Nakamura
Mid-ocean ridge basalt (hereafter, MORB) is a final product of melt generated from the partial melting of mantle peridotite, following reaction with mantle and/or lower crustral rocks, fractionation at a shallower crust and other processes en route to seafloor. Therefore, it is difficult to estimate melting processes at the upper mantle solely from any investigations of MORB. In contrast to the restricted occurrence of peridotite of mantle origin in particular tectonic settings (e.g., ophiolites, fracture zones, or oceanic core complexes), the ubiquitous presence of MORB provides us with a key to understanding global geochemical variations of the Earth's interior in relation to plate tectonics. In fact, MORB has been considered to show a homogeneous chemical composition. In terms of volcanic rocks from other tectonic settings (e.g., island arc, continental crust, ocean island), this simple concept seems to be true. However, recent investigations reveal that even MORB has significant chemical variations that seem to correspond to location (Pacific, Atlantic, and Indian Oceans). These observations suggest that the mantle beneath each ocean has a distinct chemical composition and an internally heterogeneous composition. In this paper, global geochemical variations of MORB in terms of major and trace element compositions and isotope ratios are examined using a recently compiled database. The compilation suggests that MORB has heterogeneous compositions, which seem to originate from a mixture of depleted mantle and some enriched materials. Coupled with trace element compositions and Pb-isotope ratios, there seems to be at least two geochemical and isotopic domain of the upper most mantle: equatorial Atlantic-Pacific Oceans and southern Atlantic-Indian Ocean. Material (melt and/or solid) derived from plume, subducted slab, subcontinental crust, or fluid added beneath an ancient subduction zone is a candidate to explain the enrichment end-member to produce heterogeneous MORB. Because MORB is heterogeneous, using a tectonic discrimination diagram that implicitly subsumes homogeneous MORB or its mantle sources should be reconsidered. Further investigations, particularly of off-axis MORB, are needed to understand the relationship between heterogeneous compositions of MORB and geophysical parameters (e.g., degree of melting, temperature, spreading rate, crustal thickness, etc). In addition, the role of the MOHO transitional zone should be investigated to interpret the chemical characteristics of MORB.
{"title":"Variations of Chemical Compositions of Mid-ocean Ridge Basalts (MORB) and their Origin","authors":"Hiroshi P. Sato, H. Kumagai, N. Neo, Kentaro Nakamura","doi":"10.5026/JGEOGRAPHY.117.124","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.117.124","url":null,"abstract":"Mid-ocean ridge basalt (hereafter, MORB) is a final product of melt generated from the partial melting of mantle peridotite, following reaction with mantle and/or lower crustral rocks, fractionation at a shallower crust and other processes en route to seafloor. Therefore, it is difficult to estimate melting processes at the upper mantle solely from any investigations of MORB. In contrast to the restricted occurrence of peridotite of mantle origin in particular tectonic settings (e.g., ophiolites, fracture zones, or oceanic core complexes), the ubiquitous presence of MORB provides us with a key to understanding global geochemical variations of the Earth's interior in relation to plate tectonics. In fact, MORB has been considered to show a homogeneous chemical composition. In terms of volcanic rocks from other tectonic settings (e.g., island arc, continental crust, ocean island), this simple concept seems to be true. However, recent investigations reveal that even MORB has significant chemical variations that seem to correspond to location (Pacific, Atlantic, and Indian Oceans). These observations suggest that the mantle beneath each ocean has a distinct chemical composition and an internally heterogeneous composition. In this paper, global geochemical variations of MORB in terms of major and trace element compositions and isotope ratios are examined using a recently compiled database. The compilation suggests that MORB has heterogeneous compositions, which seem to originate from a mixture of depleted mantle and some enriched materials. Coupled with trace element compositions and Pb-isotope ratios, there seems to be at least two geochemical and isotopic domain of the upper most mantle: equatorial Atlantic-Pacific Oceans and southern Atlantic-Indian Ocean. Material (melt and/or solid) derived from plume, subducted slab, subcontinental crust, or fluid added beneath an ancient subduction zone is a candidate to explain the enrichment end-member to produce heterogeneous MORB. Because MORB is heterogeneous, using a tectonic discrimination diagram that implicitly subsumes homogeneous MORB or its mantle sources should be reconsidered. Further investigations, particularly of off-axis MORB, are needed to understand the relationship between heterogeneous compositions of MORB and geophysical parameters (e.g., degree of melting, temperature, spreading rate, crustal thickness, etc). In addition, the role of the MOHO transitional zone should be investigated to interpret the chemical characteristics of MORB.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128471118","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.117.110
S. Arai, N. Abe
This article reviews interpretations of the geological and petrological nature of the Moho, which is defined as a discontinuity in terms of Vp, with a view to preparing for the Mohole on the ocean floor in IODP. We strongly propose discarding non-seismic terms for the Moho, such as “petrologic Moho”. The nature of the Moho has been controversial for a long time; an isochemical phase transition boundary between gabbro (crust) and eclogite (mantle) was favored for the Moho by some researchers, while a chemical boundary between mafic rocks (crust) and peridotite rocks (upper mantle) is now favored by a majority of researchers. Boundaries between completely or partially serpentinized peridotite and fresh peridotite may be applicable as the Moho at some parts of the ocean floors of a slow-spreading ridge origin. Antigorite serpentinite can be expected to be observed at the lowermost crust if the Moho is the serpentinization front at the stability limit of serpentine. The Moho beneath the Japan arcs can be estimated using mafic-ultramafic xenoliths in Cenozoic volcanics. Peridotitic rocks scarcely mix with feldspathic rocks, indicating that the Moho at that location is the boundary between feldspathic rocks (mostly mafic granulites ; crust) and spinel pyroxenites (mantle). Possible fossil Mohos are observed in wellpreserved ophiolites, such as the Oman ophiolite. Two types of Moho are distinct in the Oman ophiolite ; gabbro-in-dunite Moho, where a gabbro band network in dunite changes upward to the layered gabbro within a few to several tens of meters, and dunite-in-gabbro Moho, where late-intrusive dunites intruded into gabbros. The former is of a primary origin at a fast-spreading ridge, and the latter is of a secondary origin at a subduction-zone setting in the obduction of the oceanic lithosphere as an ophiolite. The gabbro/peridotite (dunite) boundary as the primary Moho forms in embryo as a wall of melt conduit at fast-spreading ridges as well as at the segment center of slow-spreading ridges. The oceanic primary Moho is modified to various degrees by magmatism, metamorphism and tectonism in subsequent arc and continental environments. The gabbro-in-dunite Moho formation in the Oman ophiolite is an embryo of this modification. We expect in-situ sampling across the primary oceanic Moho formed at a fast-spreading ridge through the Mohole of IODP. Ultra-deep drilling at gabbro/peridotite complexes exposed on the ocean floor is indispensable for our understanding of the suboceanic upper mantle. Studies on appropriate ophiolites and deep-seated xenoliths from oceanic areas should complement the Mohole and other ultra-deep drillings to grasp the whole picture of the oceanic upper mantle. * 金沢大学自然科学研究科地球学教室 ** 海洋研究開発機構地球内部変動研究センター * Department of Earth Sciences, Graduate School of Natural Science and Technology, Kanazawa University ** Institute for Research on Earth Evolution (IFREE), Independent Administrative Institution/Japan Agency for MarineEarth S
{"title":"Investigation of the Petrologic Nature of the Moho toward the Mohole","authors":"S. Arai, N. Abe","doi":"10.5026/JGEOGRAPHY.117.110","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.117.110","url":null,"abstract":"This article reviews interpretations of the geological and petrological nature of the Moho, which is defined as a discontinuity in terms of Vp, with a view to preparing for the Mohole on the ocean floor in IODP. We strongly propose discarding non-seismic terms for the Moho, such as “petrologic Moho”. The nature of the Moho has been controversial for a long time; an isochemical phase transition boundary between gabbro (crust) and eclogite (mantle) was favored for the Moho by some researchers, while a chemical boundary between mafic rocks (crust) and peridotite rocks (upper mantle) is now favored by a majority of researchers. Boundaries between completely or partially serpentinized peridotite and fresh peridotite may be applicable as the Moho at some parts of the ocean floors of a slow-spreading ridge origin. Antigorite serpentinite can be expected to be observed at the lowermost crust if the Moho is the serpentinization front at the stability limit of serpentine. The Moho beneath the Japan arcs can be estimated using mafic-ultramafic xenoliths in Cenozoic volcanics. Peridotitic rocks scarcely mix with feldspathic rocks, indicating that the Moho at that location is the boundary between feldspathic rocks (mostly mafic granulites ; crust) and spinel pyroxenites (mantle). Possible fossil Mohos are observed in wellpreserved ophiolites, such as the Oman ophiolite. Two types of Moho are distinct in the Oman ophiolite ; gabbro-in-dunite Moho, where a gabbro band network in dunite changes upward to the layered gabbro within a few to several tens of meters, and dunite-in-gabbro Moho, where late-intrusive dunites intruded into gabbros. The former is of a primary origin at a fast-spreading ridge, and the latter is of a secondary origin at a subduction-zone setting in the obduction of the oceanic lithosphere as an ophiolite. The gabbro/peridotite (dunite) boundary as the primary Moho forms in embryo as a wall of melt conduit at fast-spreading ridges as well as at the segment center of slow-spreading ridges. The oceanic primary Moho is modified to various degrees by magmatism, metamorphism and tectonism in subsequent arc and continental environments. The gabbro-in-dunite Moho formation in the Oman ophiolite is an embryo of this modification. We expect in-situ sampling across the primary oceanic Moho formed at a fast-spreading ridge through the Mohole of IODP. Ultra-deep drilling at gabbro/peridotite complexes exposed on the ocean floor is indispensable for our understanding of the suboceanic upper mantle. Studies on appropriate ophiolites and deep-seated xenoliths from oceanic areas should complement the Mohole and other ultra-deep drillings to grasp the whole picture of the oceanic upper mantle. * 金沢大学自然科学研究科地球学教室 ** 海洋研究開発機構地球内部変動研究センター * Department of Earth Sciences, Graduate School of Natural Science and Technology, Kanazawa University ** Institute for Research on Earth Evolution (IFREE), Independent Administrative Institution/Japan Agency for MarineEarth S","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115798811","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}
Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.119.519
R. Kataoka
Possible influences of cosmic rays on terrestrial climate have been studied by many researchers since a good correlation between neutron monitor counts and global cloud amount was reported by Svensmark and Friis-Christensen in 1997. The cosmic ray-cloud relationship may be best tested during Forbush decrease events, in which cosmic rays largely decrease for several days associated with coronal mass ejections. Some cloud parameters are likely to respond to the transient decrease of cosmic rays with a typical time delay of several days, although we do not know the physics behind the cosmic-ray cloud relationship.
{"title":"Cosmic Rays and Cloud Formation: Does Cloud Ammount Decrease during Forbush Decreases?","authors":"R. Kataoka","doi":"10.5026/JGEOGRAPHY.119.519","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.119.519","url":null,"abstract":"Possible influences of cosmic rays on terrestrial climate have been studied by many researchers since a good correlation between neutron monitor counts and global cloud amount was reported by Svensmark and Friis-Christensen in 1997. The cosmic ray-cloud relationship may be best tested during Forbush decrease events, in which cosmic rays largely decrease for several days associated with coronal mass ejections. Some cloud parameters are likely to respond to the transient decrease of cosmic rays with a typical time delay of several days, although we do not know the physics behind the cosmic-ray cloud relationship.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"223 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127627219","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：