Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.119.VII
S. Kiyokawa
山西省東縁に位置する太行山脈は南北に 400 kmにわたり,標高は 1,500~ 2,000 m山脈をつくる.ここでは,先カンブリア紀から 古生代にかけての連続した地層が侵食により切り立った風光明媚な地形をしており,地質公園として広く保護されている.本口絵は東 京地学協会主催の海外巡検時に訪れた公園内の地形・地質を紹介する(清川, 2010). Taihang Mountains are located eastern margin of the Shanxi Province, central China. It is more than 400 km long and is formed 1,500-2,000 m high mountain ranges. These mountain ranges are formed spectacle view of Precambrian to Paleozoic sedimentary sequence and they are taken into protective by National Geoparks in China (Kiyokawa, 2010).
位于山西省东缘的太行山脉南北绵延400公里，海拔1500 ~ 2000米。由于古生代的连续地层侵蚀，形成了陡峭的风光明媚的地形，作为地质公园受到广泛保护。本插图介绍东京地理学协会主办的海外巡检时访问的公园内的地形·地质(清川，2010). taiang Mountains are located eastern margin of the Shanxi Province，central China. It is more than 400公里long and is formed 1500 -2,000米high mountain ranges. Thesemountain ranges are formed spectacle view of Precambrian to Paleozoic sedimentary sequence and theyare taken into protective by National Geoparks in China (Kiyokawa, 2010)。
{"title":"Pictorial 2: Topographical-Geological Field Trip to Geopark in Taihang Mountains, China","authors":"S. Kiyokawa","doi":"10.5026/JGEOGRAPHY.119.VII","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.119.VII","url":null,"abstract":"山西省東縁に位置する太行山脈は南北に 400 kmにわたり,標高は 1,500~ 2,000 m山脈をつくる.ここでは,先カンブリア紀から 古生代にかけての連続した地層が侵食により切り立った風光明媚な地形をしており,地質公園として広く保護されている.本口絵は東 京地学協会主催の海外巡検時に訪れた公園内の地形・地質を紹介する(清川, 2010). Taihang Mountains are located eastern margin of the Shanxi Province, central China. It is more than 400 km long and is formed 1,500-2,000 m high mountain ranges. These mountain ranges are formed spectacle view of Precambrian to Paleozoic sedimentary sequence and they are taken into protective by National Geoparks in China (Kiyokawa, 2010).","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":"129407602","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.118.472
Shizuo Nakaya, Yoshihiro Hamada
The Lower Miocene Tanabe Group, exposed on the southern Kii Peninsula, is a thick pile of fore-arc basin sediments, which clino-unconformably covers the Paleogene Shimanto accretionary complex. Many mud diapirs and mud dykes intrude into the Tanabe Group. Several thick sequences of bedded breccia are found at Tanoi and Fukuro in Shirahama-cho, Wakayama Prefecture. In this paper, bedded breccias with shallow-marine sediments are described. The facies analysis shows that the bedded breccias are mud-volcanic deposits, and that two submarine mud volcanoes were involved in the southern Tanabe Group. The Tanoi sequences, which reach a thickness of 490 m, are mainly composed of sand-matrix, bedded breccia associated with mud-matrix, and bedded breccia. The bedded breccias range from 5 to 150 cm in thickness. They contain angular to sub-rounded clasts consisting of sandstone and mudstone from granule to cobble in size. The bedded breccia is matrix-supported with scattered clasts, which develop with inverse grading. It is considered to be a subaqueous debris flow deposit. The Fukuro sequences are mainly composed of mud-matrix, bedded breccias associated with clast-bearing sandstone of 1 ⊖ 15 cm thickness, which have turbidite-like sedimentary structures. The bedded breccias range from 5 to 150 cm in thickness. They contain angular to sub-rounded clasts consisting of mudstone and sandstone from granule to cobble in size. The bedded breccias are matrix-supported with scattered clasts, which develop with inverse grading. It is considered that the cause is a subaqueous debris flow deposit. The upper part of the clast-bearing sandstone is likely to have been reworked later by storm waves and tidal currents. The paleocurrent deduced from the sole marks of mud-matrix, bedded breccia flowed from northeast and east. The shallow-marine sediments develop wave ripple, planar cross-stratification, trough-type cross-stratification, chevron structure, off-shooting foreset, and hummocky cross-stratification, which indicate that the Fukuro mud-volcanic products were deposited at a depth near the lower limit of the storm wave base from the lower shoreface to the shelf. During the Early Miocene, submarine mud volcanism took place at Tanoi and Fukuro in the southern Tanabe Group. It is believed that the Tanoi mud volcano caused the Tanoi mud-volcanic deposits to erupt from the Tanoi mud diapir, and that the Fukuro mud volcano caused the Fukuro mud-volcanic deposits to erupt from the Migusagawa-Hirukawadani mud diapir.
{"title":"Paleo-mud-volcanoes of the Lower Miocene Tanabe Group on the Southern Kii Peninsula, Southwest Japan","authors":"Shizuo Nakaya, Yoshihiro Hamada","doi":"10.5026/JGEOGRAPHY.118.472","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.472","url":null,"abstract":"The Lower Miocene Tanabe Group, exposed on the southern Kii Peninsula, is a thick pile of fore-arc basin sediments, which clino-unconformably covers the Paleogene Shimanto accretionary complex. Many mud diapirs and mud dykes intrude into the Tanabe Group. Several thick sequences of bedded breccia are found at Tanoi and Fukuro in Shirahama-cho, Wakayama Prefecture. In this paper, bedded breccias with shallow-marine sediments are described. The facies analysis shows that the bedded breccias are mud-volcanic deposits, and that two submarine mud volcanoes were involved in the southern Tanabe Group. The Tanoi sequences, which reach a thickness of 490 m, are mainly composed of sand-matrix, bedded breccia associated with mud-matrix, and bedded breccia. The bedded breccias range from 5 to 150 cm in thickness. They contain angular to sub-rounded clasts consisting of sandstone and mudstone from granule to cobble in size. The bedded breccia is matrix-supported with scattered clasts, which develop with inverse grading. It is considered to be a subaqueous debris flow deposit. The Fukuro sequences are mainly composed of mud-matrix, bedded breccias associated with clast-bearing sandstone of 1 ⊖ 15 cm thickness, which have turbidite-like sedimentary structures. The bedded breccias range from 5 to 150 cm in thickness. They contain angular to sub-rounded clasts consisting of mudstone and sandstone from granule to cobble in size. The bedded breccias are matrix-supported with scattered clasts, which develop with inverse grading. It is considered that the cause is a subaqueous debris flow deposit. The upper part of the clast-bearing sandstone is likely to have been reworked later by storm waves and tidal currents. The paleocurrent deduced from the sole marks of mud-matrix, bedded breccia flowed from northeast and east. The shallow-marine sediments develop wave ripple, planar cross-stratification, trough-type cross-stratification, chevron structure, off-shooting foreset, and hummocky cross-stratification, which indicate that the Fukuro mud-volcanic products were deposited at a depth near the lower limit of the storm wave base from the lower shoreface to the shelf. During the Early Miocene, submarine mud volcanism took place at Tanoi and Fukuro in the southern Tanabe Group. It is believed that the Tanoi mud volcano caused the Tanoi mud-volcanic deposits to erupt from the Tanoi mud diapir, and that the Fukuro mud volcano caused the Fukuro mud-volcanic deposits to erupt from the Migusagawa-Hirukawadani mud diapir.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"171 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133391086","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.XXI
T. Urabe, J. Ishibashi
{"title":"Pictorial 1: Diversity of Subseafloor Fluid Circulation and Biosphere","authors":"T. Urabe, J. Ishibashi","doi":"10.5026/JGEOGRAPHY.118.XXI","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.XXI","url":null,"abstract":"","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"75 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":"133155070","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.118.7
R. Matsumoto
Gas hydrate, an ice-like solid compound composed of methane and water molecules, was “rediscovered” from ocean sediments in the mid-20 century, while it had been known as a chemical material to chemists and chemical engineers even in the early 19 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, stratigraphictype 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 * 東京大学大学院理学系研究科地球惑星科学専攻 * Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo
{"title":"Overview of Gas Hydrate: Impact of the Discovery of a Large Ice-like Carbon Reservoir under the Seafloor","authors":"R. Matsumoto","doi":"10.5026/JGEOGRAPHY.118.7","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.7","url":null,"abstract":"Gas hydrate, an ice-like solid compound composed of methane and water molecules, was “rediscovered” from ocean sediments in the mid-20 century, while it had been known as a chemical material to chemists and chemical engineers even in the early 19 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, stratigraphictype 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 * 東京大学大学院理学系研究科地球惑星科学専攻 * Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"23 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":"131262399","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.119.333
S. Otoh, Masanori Shimojo, K. Aoki, Takaaki Nakama, S. Maruyama, S. Yanai
We measured the 206Pb/238U age distribution of detrital zircons in five psammitic schist samples from the Sanbagawa Belt in east-central Shikoku and the western Kii Peninsula to constrain their depositional age. The age-distribution diagrams for the five psammitic schist samples all show that detrital zircons of 100 to 90 Ma are most abundant and the age of the youngest zircon in each sample is less than 80 Ma. Considering the age of the retrogressive metamorphism of these psammitic schists, ca. 80-60 Ma, the protoliths age of the psammitic schists is constrained to 75-70 Ma, correlative to the age of the sandstone of the Middle Shimanto Belt (Yanai, 1984). A similar age-distribution has already been reported for two psammitic schist samples from the Central Unit of the Sanbagawa Belt in the Kanto Mountains (Tsutsumi et al., 2009). Thus the Sanbagawa Belt is most widely occupied by metamorphic rocks originating from rocks of the Middle Shimanto Belt. We also measured the 206Pb/238U age distribution of detrital zircons in Turonian sandstone from the Northern Shimanto Belt in the central Kii Peninsula. The age-distribution diagram shows that detrital zircons of around 128 Ma are most abundant and the age of the youngest zircon in the sample is about 100 Ma. A similar age-distribution has already been reported from a psammitic schist sample from the Southern Unit of the Sanbagawa Belt in the Kanto Mountains, overlying the Central Unit (Tsutsumi et al., 2009). The protolith age is still younger than the metamorphic age of the eclogites in central Shikoku, ca. 120-110 Ma (Okamoto et al., 2004), which occupy the uppermost portion of the Sanbagawa Belt. Although some previous studies suggested that the Sanbagawa Belt consists of metamorphosed Late Jurassic to Early Cretaceous accretionary complex, the present study shows that the belt is largely occupied by metamorphosed Late Cretaceous rocks: the Shimanto Metamorphic Rocks of Aoki et al. (2007). As a result, the Sanbagawa Belt consists of the following three units with different protolith ages: (1) Lower Unit of Shimanto Metamorphic Rocks with protoliths ages of 75-70 Ma and metamorphic ages of 70-60 Ma, (2) Upper Unit of Shimanto Metamorphic Rocks with protoliths ages of 95-85 Ma and metamorphic ages of 85-75 Ma, and (3) Sanbagawa Metamorphic Rocks (s.s.) with protoliths ages of Late Jurassic to Early Cretaceous and metamorphic ages of 120-110 Ma. The protoliths of the Upper and Lower units of the Shimanto Metamorphic Rocks are most likely rocks of the Northern Shimanto and Middle Shimanto belts, respectively.
测定了四国中东部三巴川带和Kii半岛西部5个沙质片岩样品中碎屑锆石的206Pb/238U年龄分布，以约束其沉积时代。5个沙质片岩样品的年龄分布图均显示100 ~ 90 Ma的碎屑锆石最为丰富，各样品中最年轻的锆石年龄均小于80 Ma。考虑到这些沙质片岩的退变质年龄约为80 ~ 60 Ma，沙质片岩的原岩年龄限制在75 ~ 70 Ma，与中石曼托带砂岩的年龄相关(Yanai, 1984)。在关东山脉三川带中央单元的两个沙质片岩样品中已经报道了类似的年龄分布(Tsutsumi et al.， 2009)。因此，三八川带最广泛地发育了源自中石曼托带岩石的变质岩。测量了Kii半岛中部北石曼托带土伦系砂岩碎屑锆石的206Pb/238U年龄分布。年龄分布图显示，128ma左右的碎屑锆石最丰富，样品中最年轻的锆石年龄约为100ma。在关东山脉三巴川带南段的沙质片岩样本中已经报道了类似的年龄分布，该样本覆盖在中部单元上(Tsutsumi et al.， 2009)。原岩年龄仍小于四国中部榴辉岩的变质年龄，约为120 ~ 110 Ma (Okamoto et al.， 2004)，它们位于三巴川带的最上部。虽然已有研究认为三巴川带由晚侏罗世-早白垩世变质增生杂岩组成，但本研究表明，三巴川带主要为晚白垩世变质岩:Aoki et al.(2007)的Shimanto变质岩。结果表明，三巴川变质带由3个不同原岩年龄的单元组成:(1)石曼托变质岩下单元，原岩年龄为75 ~ 70 Ma，变质年龄为70 ~ 60 Ma;(2)石曼托变质岩上单元，原岩年龄为95 ~ 85 Ma，变质年龄为85 ~ 75 Ma;(3)三巴川变质岩上单元，原岩年龄为晚侏罗世~早白垩世，变质年龄为120 ~ 110 Ma。石曼托变质岩上单元和下单元的原岩极有可能分别属于石曼托北部带和石曼托中部带。
{"title":"Age Distribution of Detrital Zircons in the Psammitic Schist of the Sanbagawa Belt, Southwest Japan","authors":"S. Otoh, Masanori Shimojo, K. Aoki, Takaaki Nakama, S. Maruyama, S. Yanai","doi":"10.5026/JGEOGRAPHY.119.333","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.119.333","url":null,"abstract":"We measured the 206Pb/238U age distribution of detrital zircons in five psammitic schist samples from the Sanbagawa Belt in east-central Shikoku and the western Kii Peninsula to constrain their depositional age. The age-distribution diagrams for the five psammitic schist samples all show that detrital zircons of 100 to 90 Ma are most abundant and the age of the youngest zircon in each sample is less than 80 Ma. Considering the age of the retrogressive metamorphism of these psammitic schists, ca. 80-60 Ma, the protoliths age of the psammitic schists is constrained to 75-70 Ma, correlative to the age of the sandstone of the Middle Shimanto Belt (Yanai, 1984). A similar age-distribution has already been reported for two psammitic schist samples from the Central Unit of the Sanbagawa Belt in the Kanto Mountains (Tsutsumi et al., 2009). Thus the Sanbagawa Belt is most widely occupied by metamorphic rocks originating from rocks of the Middle Shimanto Belt. We also measured the 206Pb/238U age distribution of detrital zircons in Turonian sandstone from the Northern Shimanto Belt in the central Kii Peninsula. The age-distribution diagram shows that detrital zircons of around 128 Ma are most abundant and the age of the youngest zircon in the sample is about 100 Ma. A similar age-distribution has already been reported from a psammitic schist sample from the Southern Unit of the Sanbagawa Belt in the Kanto Mountains, overlying the Central Unit (Tsutsumi et al., 2009). The protolith age is still younger than the metamorphic age of the eclogites in central Shikoku, ca. 120-110 Ma (Okamoto et al., 2004), which occupy the uppermost portion of the Sanbagawa Belt. Although some previous studies suggested that the Sanbagawa Belt consists of metamorphosed Late Jurassic to Early Cretaceous accretionary complex, the present study shows that the belt is largely occupied by metamorphosed Late Cretaceous rocks: the Shimanto Metamorphic Rocks of Aoki et al. (2007). As a result, the Sanbagawa Belt consists of the following three units with different protolith ages: (1) Lower Unit of Shimanto Metamorphic Rocks with protoliths ages of 75-70 Ma and metamorphic ages of 70-60 Ma, (2) Upper Unit of Shimanto Metamorphic Rocks with protoliths ages of 95-85 Ma and metamorphic ages of 85-75 Ma, and (3) Sanbagawa Metamorphic Rocks (s.s.) with protoliths ages of Late Jurassic to Early Cretaceous and metamorphic ages of 120-110 Ma. The protoliths of the Upper and Lower units of the Shimanto Metamorphic Rocks are most likely rocks of the Northern Shimanto and Middle Shimanto belts, respectively.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"151 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":"124205493","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.VI
C. Aoyama, Maki Suzuki, R. Matsumoto
{"title":"Pictorial 6: Observation and Analysis of Methane Plume","authors":"C. Aoyama, Maki Suzuki, R. Matsumoto","doi":"10.5026/JGEOGRAPHY.118.VI","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.VI","url":null,"abstract":"","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"59 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":"116243120","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.118.1265
K. Arai
Investigations of disasters caused by past earthquakes are useful when taking measures against earthquake disasters that may occur in the near future. In western Saitama Prefecture, there have been few reports so far on damage caused by earthquakes occurring beneath the Tokyo metropolitan area; however, a remarkable description was found in the annual report of the Central Meteorological Observatory of Japan. According to the report, a slope in Hanno town failed over a width extending 640-660 m caused by the 1894 Meiji Tokyo earthquake. The author investigated the location of the failed slope and details of damage. A family in Kusumi, Hanno city (Hanno town at that time), suffered from a landslide caused by a past earthquake which is considered to be the 1894 Meiji Tokyo earthquake. The slope beside their residence extends for about 700 m to the east along the Hirayama ridge, and descends steeply toward the Iruma River. Many scars from small landslides are left on the entire surface of the slope. These topographical features suggest that several landslides occurred on this slope following the 1894 Meiji Tokyo earthquake. As a result, the author has come to the conclusion that the failed slope reported by the Central Meteorological Observatory of Japan was located along the Hirayama ridge, and several landslides occurred on this slope. It is possible to recognize that a strong quake shook Hanno town, which is located far from the epicenter.
{"title":"Slope Failure Caused by 1894 Meiji Tokyo Earthquake in Hanno Town, Koma County, Saitama Prefecture","authors":"K. Arai","doi":"10.5026/JGEOGRAPHY.118.1265","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.1265","url":null,"abstract":"Investigations of disasters caused by past earthquakes are useful when taking measures against earthquake disasters that may occur in the near future. In western Saitama Prefecture, there have been few reports so far on damage caused by earthquakes occurring beneath the Tokyo metropolitan area; however, a remarkable description was found in the annual report of the Central Meteorological Observatory of Japan. According to the report, a slope in Hanno town failed over a width extending 640-660 m caused by the 1894 Meiji Tokyo earthquake. The author investigated the location of the failed slope and details of damage. A family in Kusumi, Hanno city (Hanno town at that time), suffered from a landslide caused by a past earthquake which is considered to be the 1894 Meiji Tokyo earthquake. The slope beside their residence extends for about 700 m to the east along the Hirayama ridge, and descends steeply toward the Iruma River. Many scars from small landslides are left on the entire surface of the slope. These topographical features suggest that several landslides occurred on this slope following the 1894 Meiji Tokyo earthquake. As a result, the author has come to the conclusion that the failed slope reported by the Central Meteorological Observatory of Japan was located along the Hirayama ridge, and several landslides occurred on this slope. It is possible to recognize that a strong quake shook Hanno town, which is located far from the epicenter.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"19 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":"124656751","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.119.568
Hidetsugu Yoshida
The Japanese Islands are tectonically active and humid. Thus, erosion and deposition are the primary processes controlling geomorphic development. Catastrophic sector collapses at volcanoes should be considered significant in this context. This study examines the geomorphological role of volcanic sector collapses in Japan, introducing 58 cases with their respective occurrence ages and volumes (≥ 1×108 m3). We find that the frequency of sector collapses becomes exponentially higher as the collapse magnitude decreases. The total volume of the dissected volcanic edifice caused by catastrophic collapses amounts to ca. 6.4 km3 (640×108 m3) during the last 500 years. This value can be translated into an annual denudation rate of 0.53 mm/y per unit area of the Quaternary volcanoes (ca. 24000 km2), which is comparable to the contemporary denudation rate of non-volcanic mountains in Japan. Therefore, although volcanic sector collapses occur intermittently, we have to consider them as sediment sources that are indispensable to an understanding of geomorphology in Japan.
{"title":"Catastrophic Sector Collapses of Quaternary Volcanoes as Significant Sediment Sources in Japan","authors":"Hidetsugu Yoshida","doi":"10.5026/JGEOGRAPHY.119.568","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.119.568","url":null,"abstract":"The Japanese Islands are tectonically active and humid. Thus, erosion and deposition are the primary processes controlling geomorphic development. Catastrophic sector collapses at volcanoes should be considered significant in this context. This study examines the geomorphological role of volcanic sector collapses in Japan, introducing 58 cases with their respective occurrence ages and volumes (≥ 1×108 m3). We find that the frequency of sector collapses becomes exponentially higher as the collapse magnitude decreases. The total volume of the dissected volcanic edifice caused by catastrophic collapses amounts to ca. 6.4 km3 (640×108 m3) during the last 500 years. This value can be translated into an annual denudation rate of 0.53 mm/y per unit area of the Quaternary volcanoes (ca. 24000 km2), which is comparable to the contemporary denudation rate of non-volcanic mountains in Japan. Therefore, although volcanic sector collapses occur intermittently, we have to consider them as sediment sources that are indispensable to an understanding of geomorphology in Japan.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"21 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":"132334712","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.119.279
K. Kunugiza, A. Goto
This paper examines the early stage of the geotectonic history of the Japanese Islands on the basis of finding hydrothermal jadeitite including zircons of ca. 520 Ma in serpentinite melange of the Itoigawa-Omi area of the Hida-Gaien belt, Central Japan. Hydrothermal jadeitite contains euhedral jadeite in natrolite veins and patches, and consists of jadeite-albite and jadeite-natrolite without quartz. These minerals were crystallized from an aqueous fluid phase at the low-pressure and high-temperature side of the reaction boundary of albite = jadeite + quartz in the system NaAlSiO4-SiO2-H2O. The occurrence of rounded relict hornblende mantled by omphacite rimmed by fine-grained aggregates of jadeite in the matrix of jadeite and albite suggests a pervasive hydrothermal fluid flow, through which metabasite was extensively replaced by jadeitite. This rather high-temperature hydrothermal activity of ca. 520 Ma did not occur in an ordinary subduction zone but in a newly-formed mantle wedge suffering severe hydration from a subducting slab. Recently accumulated U-Pb ages of zircon of ca. 450-500 Ma from paleozoic sediments and granitic rocks of the Hida-Gaien belt were due to initiation of subduction followed by subduction zone magmatism. Protolith of serpentinite in the Hida-Gaien belt includes highly depleted harzburgite, thus requiring tectonic setting of a high-temperature-rift zone rather than a low-temperature-slow spreading ridge. Subduction was initiated at ca. 520 Ma along the boundary between low-density harzburgitic rift zone peridotite and lherzolitic spreading ridge peridotite with a slightly higher density, resulting in the common occurrence of harzburgitic serpentinite in the oldest part of the accretionary complex of Southwest Japan. An area including the Japanese Islands was born around the Yangtze block by the breaking up of the Rodinia supercontinent, because the oldest K-Ar age of biotite actinolit rock of 672 Ma (Matsumoto et al., 1981) and the subduction initiation of ca. 520 Ma are in accord with the paleogeographic history of the Yangtze block, and because ca. 300 Ma Renge schists of the Hida-Gaien belt did not suffer the ca. 280-200 Ma collision-type metamorphism of the Hida metamorphic belt that is an eastern extension of the suture between the Sino-Korea and Yangtze blocks.
本文通过在日本中部飞驒-盖园带伊藤川-尾尾地区的蛇纹岩混杂岩中发现含锆石约520 Ma的热液翡翠岩，对日本列岛早期大地构造史进行了研究。水热硬岩体在钠石脉和斑块中含有自形硬石，由硬石-钠长石和硬石-钠长石组成，不含石英。这些矿物在NaAlSiO4-SiO2-H2O体系中钠长石=硬石+石英反应边界的低压高温侧由水相结晶而成。在硬玉和钠长石的基质中，出现了以辉长石为包覆的圆形残余角闪石，边缘为细粒硬玉集合体，表明热液流体普遍存在，其中辉长石被硬玉广泛取代。约520 Ma的高温热液活动并非发生在普通的俯冲带，而是发生在俯冲板块剧烈水化作用下新形成的地幔楔中。飞达-盖延带古生代沉积物和花岗质岩石中锆石的最近累积U-Pb年龄约为450 ~ 500 Ma，这是由俯冲带岩浆作用引起的。Hida-Gaien带蛇纹岩原岩中含有高度亏缺的辉锌矿，因此要求构造背景为高温裂谷带而非低温慢扩张脊。约520 Ma时，沿密度稍高的低密度辉闪质裂谷带橄榄岩与密度稍高的辉闪质扩张脊橄榄岩的分界线开始俯冲，导致辉闪质蛇纹岩在日本西南增生杂岩最古老部分普遍赋存。由于672 Ma (Matsumoto et al.， 1981)的最古老黑云母放光岩K-Ar年龄和约520 Ma的俯冲起始时间与扬子地块的古地理历史相吻合，Rodinia超大陆的分裂在扬子地块周围形成了包括日本列岛在内的区域。因为约300 Ma的飞驒-盖恩带的仁阁片岩没有受到约280-200 Ma的碰撞变质作用，而飞驒变质带是中朝-扬子地块缝合线的东延。
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Pub Date : 1900-01-01DOI: 10.5026/JGEOGRAPHY.117.948
T. Minami
The present study represents an attempt to determine the sources of vermilion found in ancient Japanese burial mounds prior to the emergence of the ancient Yamato dynasty. For this purpose, cinnabar ores were collected from Chinese and Japanese mines, and samples of vermilion were also collected from ancient tombs. When the vermilion collected from the tombs was studied morphologically, different particle sizes were observed. However, the particle size of the artificial vermilion was found almost same. The metal contents of cinnabar ores were different for each Japanese mine: Niu (Mie Pref.), Yamato Mercury (Nara Pref.), Sui (Tokushima Pref.), and Itomuka (Hokkaido Pref.) mines. Arsenic (As) content was highest in cinnabar ore from Niu mine; Mn and Fe contents were highest in Yamato Mercury mine; and, the Ba, Ca, Co, Cr, and Sr contents were highest in Sui mine. When analyzing the metal contents of vermilion collected from ancient tombs in Nara Prefecture, vermilion collected from Kurozuka, Kamotsuba, and Tomio-Maruyama tombs showed a high As content, and vermilion from Tenjinyama tomb showed a high Mn content. Thus, the possibility was suggested of identifying the original vermilion mine from the metal contents. However, it is difficult to set borderlines for the metal contents of vermilion to identify the source mine. So, the ratios of sulfur isotope (δ34S) in ores and vermilion were compared. A high δ34S value of +22.6 ± 3.6‰ was found for the ore of Wanshan of Guizhou and from +6 to +10.6‰ for Xunyang of Shaanxi in China, as opposed to low values ranging from -7.3 ± 1.9 to -2.1 ± 1.6‰ for Japanese mines. It is thought that δ34S values are suitable for determining the sources of vermilion found in ancient tombs. In addition, high ratios from +7.4 to +22.8‰ were found in 1st- and 2nd-century burial sites in northern Kyushu and San'in, and lower ratios from -8.4 to -2.0‰ were found in burial sites of the 2nd through 6th centuries in central Japan. Therefore, powerful local chiefs living in northern Kyushu and San'in areas might have obtained vermilion through relations with China, but chiefs living in central Japan might have used vermilion collected from Japanese mines. In conclusion, the sources of vermilion collected in ancient tombs can be determined by measuring δ34S values. An additional analysis of a lead isotope ratio, for example, might also be necessary to determine the source of vermilion.
{"title":"Sources of Vermilion Collected from Ancient Japanese Tombs","authors":"T. Minami","doi":"10.5026/JGEOGRAPHY.117.948","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.117.948","url":null,"abstract":"The present study represents an attempt to determine the sources of vermilion found in ancient Japanese burial mounds prior to the emergence of the ancient Yamato dynasty. For this purpose, cinnabar ores were collected from Chinese and Japanese mines, and samples of vermilion were also collected from ancient tombs. When the vermilion collected from the tombs was studied morphologically, different particle sizes were observed. However, the particle size of the artificial vermilion was found almost same. The metal contents of cinnabar ores were different for each Japanese mine: Niu (Mie Pref.), Yamato Mercury (Nara Pref.), Sui (Tokushima Pref.), and Itomuka (Hokkaido Pref.) mines. Arsenic (As) content was highest in cinnabar ore from Niu mine; Mn and Fe contents were highest in Yamato Mercury mine; and, the Ba, Ca, Co, Cr, and Sr contents were highest in Sui mine. When analyzing the metal contents of vermilion collected from ancient tombs in Nara Prefecture, vermilion collected from Kurozuka, Kamotsuba, and Tomio-Maruyama tombs showed a high As content, and vermilion from Tenjinyama tomb showed a high Mn content. Thus, the possibility was suggested of identifying the original vermilion mine from the metal contents. However, it is difficult to set borderlines for the metal contents of vermilion to identify the source mine. So, the ratios of sulfur isotope (δ34S) in ores and vermilion were compared. A high δ34S value of +22.6 ± 3.6‰ was found for the ore of Wanshan of Guizhou and from +6 to +10.6‰ for Xunyang of Shaanxi in China, as opposed to low values ranging from -7.3 ± 1.9 to -2.1 ± 1.6‰ for Japanese mines. It is thought that δ34S values are suitable for determining the sources of vermilion found in ancient tombs. In addition, high ratios from +7.4 to +22.8‰ were found in 1st- and 2nd-century burial sites in northern Kyushu and San'in, and lower ratios from -8.4 to -2.0‰ were found in burial sites of the 2nd through 6th centuries in central Japan. Therefore, powerful local chiefs living in northern Kyushu and San'in areas might have obtained vermilion through relations with China, but chiefs living in central Japan might have used vermilion collected from Japanese mines. In conclusion, the sources of vermilion collected in ancient tombs can be determined by measuring δ34S values. An additional analysis of a lead isotope ratio, for example, might also be necessary to determine the source of vermilion.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"26 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":"126171508","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}
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