著者
磯崎 行雄
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.114, no.3, pp.410-418, 2005-12-25 (Released:2009-11-12)
参考文献数
14

Current trends in research on history of life are briefly reviewed. Since the 1990s study on deep past focusing on early life on Earth and Mars has become popular. This trend often called astrobiology will be a main stream in earth science in this century because it involves the latest human issues, such as global environment, energy, food, world population, and search for habitable planets outside the solar system, in addition to conventional studies on the evolution of Earth and life. Studies on chemofossils of nanometric scale and on geochemical proxies for evaluating paleoenvironments will be the most important targets in this research field. Inevitable in Japan are overhaul of the current domestic-oriented atmosphere in the geological community and deployment of a new research style under a long-term scope.
著者
堤 之恭 沢田 輝 磯﨑 行雄
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.127, no.5, pp.723-734, 2018-10-25 (Released:2018-11-14)
参考文献数
47
被引用文献数
3 3

Zircon is the only candidate of Hadean terrestrial material that can be collected because it can survive physically and chemically, as well as maintain its U–Pb age system during omnigenous geological events. However, Hadean zircons are rare, so many age analyses of zircons are required to isolate Hadean zircon grains. There are two ways to improve the analyses; decrease the time required for pre-analyzing processes and decrease the time required for age analysis. New equipment, high-voltage pulse power fragmentation device and automatic zircon pick-up system are effective for crushing rock sample and separating zircon grains, respectively, in a short time. Another potential age analysis, the 207Pb/206Pb age screening analysis, shows good performance in selecting old zircons quickly. Integrative operation of equipment and methods will result in successfully finding numerous Hadean zircons.
著者
道林 克禎
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.93-109, 2008-02-25 (Released:2010-02-10)
参考文献数
74
被引用文献数
9 9

Peridotites derived from the uppermost mantle consist dominantly of olivine and subsequently of pyroxene, spinel, garnet, and plagioclase. Crystal-plastic flow of mantle rocks results in various types of structure within peridotite being developed to varying degrees, depending upon the structure sensitivity of the different mineral phases. Plastic deformation leads to the simultaneous development of shape-preferred orientations and crystal-preferred orientations. A shape-preferred orientation is the expression of the average orientation of flattening (foliation) and elongation (lineation) directions, as defined by the orientations of individual grains. A crystal-preferred orientation (CPO) is the expression of crystallographic orientations of grains within the rock, as developed via dislocation creep and recrystallization. During intense homogeneous plastic deformation of a peridotite composed of minerals with a dominant slip system, the preferred orientation of the slip plane and slip direction tends to coincide with the plane of plastic flow and the flow direction, respectively. Recently, a new olivine CPO classification (A, B, C, D, and E types) has been proposed by Karato and co-workers to illustrate the roles of stress and water content as controlling factors of olivine slip systems. An additional CPO type (AG) has also been proposed in recognition of its common occurrence in nature. Given that olivine and the other constituent minerals in peridotites contain intrinsic elastic anisotropies, the development of CPO within peridotite during plastic deformation gives rise to seismic anisotropy in the upper mantle. Thus, the anisotropic properties of mantle rocks derived from the upper 100 km of the mantle, such as Ichinomegata peridotite xenoliths from the northeast Japan arc, have been calculated and applied with the aim of understanding the seismic anisotropy of the Earth's mantle.
著者
新谷 俊一 田中 和広
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.3, pp.340-349, 2009-06-25 (Released:2010-03-26)
参考文献数
20
被引用文献数
12 12

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.
著者
増田 隆一
出版者
公益社団法人 東京地学協会
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.105, no.3, pp.354-363, 1996-06-25
参考文献数
29
被引用文献数
1

The richness of fauna diversity is seen on the Japanese Islands, which range through 3, 000 km. When and from where have theanimals immigrated to Japan? Also, for understanding natural history of the Japanese Islands, it is very importantto investigate evolutinary history and origin of animals distributed on each island. While the evolutionary questions have been paleontologically and geologically examined so far, some of them are still unclear. Recent development of molecular phylogenetic study provides a reliable sight to understanding evolutionary history and origin of species. Advantageously, molecular study can analyze phylogeny of living species without fossil data.<BR>In Japan, two wildcats, the Iriomote cat and the Tsushima cat, live on the Iriomote Island and the Tsushima Island, respectively, where land bridges between the Asian continent and the Japanese Islands were present in the past time. To know evolution of these wildcats gives us useful information for better understanding of natural history of the Japanese Islands. Moreover, because both the wildcats are now endangered, it is now strongly needed to understand phylogenetic status of them for conservation and management. For the reason, we investigated molecular phylongeny of the two wildcats based on mitochondrial DNA sequences, and revealed that both the wildcats are very closely related to the leopard cat <I>Felis bengalensis</I>, which is widespread throughout Asia. Furthermore, from the DNA data, the Iriomote cat and the Tsushima cat were estimated to have diverged from the continental leopard cat approximately 200, 000 and 100, 000 years before present, respectively. The dates estimated by molecular data were in concordance with formation dates of the Ryukyu Arc and the Tsushima Island, respectively. These results suggest that geographic barrier has led fixation of some unique morphological characters into each cat population, while the two Japanese wildcats are still genetically close to the continental leopard cat.
著者
村上 亮 飛田 幹男 矢来 博司 小澤 慎三郎 西村 卓也 中川 弘之 藤原 智
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.109, no.6, pp.944-956, 2000-12-25 (Released:2009-11-12)
参考文献数
23
被引用文献数
1 1

The power of interferometric Synthetic Aperture Radar (SAR) when applied to studies of crustal deformation has been fully demonstrated by Massonnet et al. (1993, 1994) and Zebker et al. (1994) for the Landers, California earthquake of June 28, 1992. This method is unique in its capability of providing a two-dimensional representation of a deformation with a dense spatial coverage over most of the globe. Since 1994, the Geographical Survey Institute (GSI) has been conducting a study on applications of differential InSAR (Interferometric SAR) for the detection of crustal deformations associated with earthquakes and volcanic activities. Crustal deformations of many episodes were mapped by InSAR, such as those due to the 1994 Northridge earthquake, the 1995 Hyogo-ken Nanbu earthquake, the 1995 Neftegorsk earthquake, and volcanic deformations of Mt. Iwate and Mt. Usu. These interferograms played an important role in constructing geophysical models.
著者
岩森 光
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.116, no.1, pp.174-187, 2007-02-25 (Released:2009-11-12)
参考文献数
56
被引用文献数
1

To understand the transportation and the circulation of water in subduction zones and the mantle, the maximum H2O content of rocks under variable pressure-temperature conditions was reviewed. The maximum H2O content is also important for assessing the potential storage of H2O in the mantle, which shows that the mantle can contain 4.6 to 12.5 times more H2O than the current ocean mass, assuming a standard geothermal gradient. Although the estimation has a large degree of uncertainty, the mantle is a significant storage, and plays an important role in global water circulation, especially due to the unexpectedly high capacities of nominally anhydrous minerals (NAMs). Based on this information, water circulation in subduction zones (especially in the Japanarcs) and the mantle has been discussed with the relevant numerical modeling and geophysical and geological observations. Consequently, the following points have been clarified : (1) breakdown depths of the major hydrous minerals within and around the subducting slab depend on the thermal structure (deeper for colder environments); (2) when a hot slab, including a spreading mid-ocean ridge, subducts, both water and heat are supplied to the forearc region, contributing to the formation of regional metamorphic belts; (3) both high-pressure-type and high-temperature-type metamorphism occur within a limited time in a single forearc domain associated with ridge subduction ; (4) arc magmatism and regional metamorphism are regarded as a series of geological events corresponding to different stages of a temporal change in the thermal state of a subduction zone; (5) although major dehydration of subducting slabs occurs at depths shallower than 200 km, triggering arc magmatism or regional metamorphism, the subducting slab and the bottom portion of the overlying mantle wedge above the slab transport several 100 to several 1000 ppm of H2O with NAMs to the transition zone ; (6) the influx of H2O into the transition zone by this mechanism is comparable to or exceeds outgassing by magmatism at mid-ocean ridges and hotspots; (7) the influx was suppressed in the past where the potential temperature was high (hot-dry regime), while it will be enhanced in the future as the Earth cools (cold-wet regime), resulting in stabilization and prolongation of mantle convection; and, (8) considering the presence of very cold subduction zones such as central Japan, where a significant amount of water is exceptionally transported to the deep mantle, the present-day Earth is probably in a transition from a hot-dry regime to a cold-wet regime. In any case, the maximum H2O content in NAMs in the upper mantle controls the influx, which needs to be constrained tightly for more accurate estimations of global water circulation.
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.131, no.3, pp.Cover03_01-Cover03_02, 2022-06-25 (Released:2022-07-08)
参考文献数
2

西南日本から連続する中央構造線(MTL)は,群馬県西部下仁田地域を通過し,北側に領家帯の白亜紀花崗岩類や美濃・丹波帯(=足尾帯)のジュラ紀付加体が,南側に三波川帯の白亜紀高圧型片岩が広く露出する.MTLのすぐ南側には,低角度断層を介して三波川変成岩の上に特異な岩石・地層群がクリッペとして累重する.「跡倉クリッペ」はペルム紀花崗岩やホルンフェルス,非変成の白亜系–古第三系礫岩・砂岩など,どれも少量だが多様な岩石から構成される.1950年代から研究されはじめたが,その起源は長らく謎であった.写真は,下仁田南方の南牧川沿いに露出する逆転した跡倉層の下部白亜系砂岩・泥岩交互層である.近年,同層を含む関東山地の白亜紀砂岩中の砕屑性ジルコンのU–Pb年代が測定され(中畑ほか, 2015, 2016),跡倉層には原生代(25-15億年前)粒子が大量に含まれることが判明した.同じ関東山地でも約10 km南方の秩父帯の同時代砂岩とは大きく異なる後背地をもつこと,また西南日本では飛騨帯と舞鶴帯にのみ知られるペルム紀花崗岩を随伴することから,跡倉クリッペは関東でできた岩石群ではなく,もともと中生代日本の大陸側に起源をもち,二次的に長距離(最大100 km程度)移動してきた岩体と推定される.こんにゃくとネギで有名な下仁田地域の地質には,日本列島のルーツに関する秘密が隠されている.地元を走る上信電鉄の車体に大きくペイントされた「跡倉クリッペ」の文字をみて嬉しくなるのは「撮り鉄」ファンだけではないだろう.(写真・解説:磯﨑行雄)
著者
ビルンド エリック 岩田 修二
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.90, no.2, pp.112-121, 1981-04-25 (Released:2010-11-18)
被引用文献数
1

フィンランド・ノルウエー・スウェーデンの北部に35, 000人ほどいるラップ人のうち, 山地の森林限界以上に居住する山地ラップ人と, 低地の森林に居住する森林ラップ人とは, 暮らし方がかなりちがっている。森林ラップ人の生活は古い時代のラップ人の生活様式を色濃く残している。ごく最近まで, 森林ラップ人は狩猟や漁労 (これらはラップ人の古い生業形態である) を生業にしていた。トナカイの飼育を始めたのは最近で, 飼っている頭数も少なく, 移動範囲もせまい。山地ラップ人が牧畜を始めたのもそれほど古いことではなく, 16-17世紀である。そして, およそ100年前には完全に牧畜(移牧)だけに依存するようになった。夏には高山地域へ, 冬には森林地域へ移動し, 春と秋は亜高山帯で過す。移動距離は数100kmにも達している。山地ラツプ人の生活基盤は牧畜業にあると考えられがちであるが, 現在では牧畜だけで生活しているラップ人の数はたいへん少数になった。スウェーデンの場合, ラップ人口のうちの7%ないし25%にすぎない。17世紀後半には, ラップランドにはラップ人だけが居住していた。そこへ, 南からの移住農民が侵入するにつれて, いろいろの問題がおこり始めた。これに対する政府の立場は, スウェーデンの場合, 土地は広大であり, 移住農民と牧畜ラップ人とは生活の場が異なるから摩擦は起きないであろうというものであった。しかし, 現実には多くの問題が起き, ラップ人はいつも不利益をこうむってきた。政府が長年ラップ人を保護し, 生活水準・教育水準を高めてきたとはいうものの, 少数民族であることと, 牧畜という不安定な生業に依存していることとのために問題の根本解決はなされていない。ラップランドからの人口流出が20世紀半ばから始まったことによって, ラップ人がラップランドとその周辺でスウェーデン人に雇用される機会が減った。いっぽう, ラップ人に対する人種偏見は減り, ラップ人がスウェーデン社会にとけこみやすくなった。しかし, これがラップの固有文化の崩壊をはやめることになった。現在では都市で生活しているラップ人も多い。
著者
W. G. ERNST
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.106, no.5, pp.735-738, 1997-10-25 (Released:2009-11-12)

The strategic justification for supporting scientific activities has largely depending on the understanding that research provided both national security in a time of global hostility involving the improvement of the economy, greater social equity, better health, better race relations, and enhancement of environmental quality, and widespread health benefits. In terms of curriculum in the Earth Sciences, the important point here is that study courses must evolve to accommodate the changing, enlarging body of knowledge as well as the ultimate career needs of the future degree holders. Growing subdisciplines needed in America include hydrology, hydrogeology, neotectonics, continental margin oceanography, engineering geology, geologic hazards, environmental science, aqueous geochemistry, and material sciences. Metamorphic petrologists are especially well-equipped with the fundamental knowledge from physics and chemistry as well as geology to treat the problems society wishes to address and solve. The situation provides us with a natural advantage, but to realize it, we must move our emphasis away from the traditional topics of metamorphic petrology.
著者
代田 寧 大場 武 谷口 無我 十河 孝夫 原田 昌武
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.130, no.6, pp.783-796, 2021-12-25 (Released:2022-01-28)
参考文献数
24
被引用文献数
2 2

Earthquake swarms have occurred with volcanism repeatedly at Hakone volcano in Kanagawa prefecture, Japan. In 2015, a phreatic eruption took place about two months after the start of an earthquake swarm. Hakone volcano is a popular tourist destination. If it is possible to forecast at the early stages of an earthquake swarm whether or not an eruption will occur, the forecast could contribute to preventing disasters involving tourists. At Hakone volcano, increases in the ratio of components (CO2/H2S) contained in the volcanic gas from fumaroles were observed in synchronization with earthquake swarms and ground deformation in 2013 and 2015. Similar increases in CO2/H2S ratio were also observed in 2017 and 2019, although the increases in the CO2/H2S ratio in 2017 and 2019 were not as sharp as those in 2013 and 2015. Furthermore, the maximum values of the CO2/H2S ratio in 2017 and 2019 were lower than the values in 2013 and 2015. These differences in the CO2/H2S ratio may be related to the limited and smaller scale of volcanic activity in 2017 and 2019 relative to 2013 and 2015. Another explanation for the difference is a possible irreversible change in the underground structure of the Owakudani area, which is a geothermal area around Hakone volcano, because the phreatic eruption took place in the Owakudani area in 2015. During all four seismically active periods in 2013, 2015, 2017, and 2019, the CO2/H2S ratio decreased simultaneously with decreases in the number of volcanic earthquakes. The lower limit of CO2/H2S ratios after the peak of the CO2/H2S ratio time series was about 20 in all periods. This implies that subsequent unrest would not start until the CO2/H2S ratio drops to about 20. The CO2/H2S ratio might be an effective tool for forecasting activity at Hakone volcano. During the active periods in 2013, 2015, 2017, and 2019, extensions of the baseline across Hakone volcano were observed by GNSS with increases in the CO2/H2S ratio. A good correlation was found between the extensional velocity of the baseline length and the increasing rate of the CO2/H2S ratio. These variations could be examined at the early stage of unrest. The findings argue that the CO2/H2S ratio is a promising tool for predicting and evaluating volcanic activity at Hakone volcano.

1 0 0 0 OA 鉱物と宝石

著者
宮田 雄史
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.131, no.2, pp.275-288, 2022-04-25 (Released:2022-05-13)
参考文献数
20
被引用文献数
2

Gems must meet three requirements: be beautiful, be durable, and be rare. The concept beauty depends on personal values. It is, therefore, not something that is objective and separate from human society. Gems have relationships with society and have requirements. That is, it must be determined whether a gem is genuine or fake. Gems are essentially natural materials. They are generally minerals that are naturally occurring solids formed by geological processes. However, gems have a cultural aspect depending on how they are used. In a historical review, how these two aspects of gems have become the subject of scholarship is briefly elucidated. Currently, artificial gem materials are classified according to their growth history, and whether they are synthetic, man-made, imitations or composites. The task of defining these categories, in addition to natural gems and treated gems, is gem identification, which is based on gem variety, genesis (natural or artificial), treatments applied, (quality) origin (locality) and individual recognition. The development and current status of gemology is reviewed from the viewpoint of mineralogy.
著者
赤井 純治
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.131, no.2, pp.213-233, 2022-04-25 (Released:2022-05-13)
参考文献数
62
被引用文献数
2

One of the most significant developing fields in mineralogy during the last quarter century involves interactions between microbes and minerals in the environment. A mineral evolution has been suggested. The fundamentals of biominerals, interactions between biosphere and minerals, and expanding knowledge of the biosphere are presented. Interactions between minerals and microbes are closely related to the evolution of the Earth's surface environment, and they suggest keys for solving environmental problems on the Earth. They are also related to the search for extraterrestrial life. This review sketches a brief history of mineralogy, referring to TEM methods, concerning regularity, irregularity, and interactions of minerals.
著者
土`山 明 松野 淳也
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.131, no.2, pp.193-211, 2022-04-25 (Released:2022-05-13)
参考文献数
32
被引用文献数
2

Chondritic-porous interplanetary dust particles (CP IDPs) originating from comet and carbonaceous chondrites of asteroids are primitive materials in the solar system. This paper reviews our recent research by mineralogical approach on the primitive materials, which include reproduction experiments of glass with embedded metal and sulfide (GEMS) in CP IDPs, detailed three-dimensional structures of GEMS, and discoveries of ultra-porous lithology as a “fossil of ice” in primitive carbonaceous chondrites and CO2-rich fluid inclusions in calcites of an aqueously-altered carbonaceous chondrite based on multi-scale three-dimensional observations. From the results, together with recent dynamic models of solar system formation, a new united model of the formation and evolution of primitive materials in the solar system is proposed as a working hypothesis. In this model, GEMS or GEMS-like materials corresponding to matrices of carbonaceous chondrites form due to the evaporation of precursors followed by condensation and chondrules due to melting followed by solidification in the highest temperature and moderately-high temperature regions, respectively, through a single local heating event. These local events occur at different distances from the sun and the high-temperature products were aggregated into comets and parent bodies of carbonaceous chondrites with ice and organic materials.
著者
大谷 栄治
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.131, no.2, pp.179-192, 2022-04-25 (Released:2022-05-13)
参考文献数
63
被引用文献数
2

Various phase transitions occur in the Earth's interior. They cause discontinuities in seismic velocity and density profiles. The 410 km and 660 km discontinuities are explained by the olivine–wadsleyite transformation and the decomposition of ringwoodite into ferropericlase and bridgmanite, respectively. The major transitions in the lower mantle are the spin transition in mantle minerals containing ferric and ferrous irons, the post-perovskite transition of bridgmanite, i.e., the transformation of bridgmanite into a post-perovskite phase with a CaIrO3 structure. The former transition may occur at the shallow lower mantle, whereas the latter transition occurs at the bottom of the lower mantle, which may correspond to the D″ layer at the core–mantle boundary. There are several important seismic velocity anomalies. These include low-velocity anomalies associated with hot rising mantle plumes and oceanic ridge areas, and high-velocity anomalies associated with cold slab subduction. Ocean water is returned into the mantle by hydrous minerals stored in the slabs. Some hydrous minerals such as the solid solution of hydrous phase δ and phase H, AlOOH-MgSiO4H2 are stable along the normal geotherm to the core–mantle boundary, and bring water into the base of the lower mantle. Another interesting region is located at the base of the lower mantle. These anomalies are called the Large Low Shear Velocity Provinces (LLSVP) and the Ultra-Low Velocity Zones (ULVZ). An LLSVP is considered to be a region with iron enrichment. This region may be caused by accumulations of the high-pressure hydrous phases. A ULVZ with very low compressional and shear velocities and high densities is observed at the core–mantle boundary. This region may contain dense iron rich melts. The Earth's core is composed of a molten outer core and a solid inner core. It consists mainly of iron–nickel alloy with small amounts of light elements, such as Si, O, S, C and H. The inner core is considered to be composed of an hcp phase. However, some enigmatic properties of the inner core, such as low shear velocity and anisotropy, may not be explained only by this phase. Some experimental and theoretical studies suggest the existence of a bcc phase at a high temperature region approaching the melting temperature. Therefore, the inner core may be composed of a bcc phase or a mixture of hcp and bcc (or B2 phase which is an ordered form of the bcc structure). Further studies are necessary to achieve a better understanding of the Earth's core.