Gold Mineralization in Izu Peninsula,Central Japan,during Crustal Extension in Response to Double Subduction     

Keiko Hattori  Ken‐ichi Kano 《Resource Geology》2019,69(2):167-175

Izu Peninsula in central Japan, the northern tip of the Izu‐Bonin arc, hosts numerous epithermal Au–Ag vein deposits of low‐sulfidation style. All have similar vein textures, mineralogy, and alteration. Geochemical data from fluid inclusions in vein quartz, the mineralogy and mineral chemistry of alteration, and stable isotope data indicate that auriferous hydrothermal activity occurred under subaerial conditions. The K–Ar ages of auriferous vein minerals are <1.5 Ma, indicating that the mineralization took place after extensive submarine volcanism for the host rocks. These observations suggest that Au–Ag mineralization was synchronous with the development of an extensional regime of the Izu block after its collision with the Honshu arc after 1.5 Ma. This collision resulted in the shifting of the Izu block far from the trench to the rear position, and the subduction of the Izu block along the Suruga trough to the west and along the Sagami trough to the east. The reararc position of the Izu block and double subduction resulted in crustal extension, upwelling of asthenospheric mantle, and tholeiitic magmatism reflected by mafic dyke swarms and subsequent monogenetic volcanic activity in the Izu peninsula. The timing of the Au mineralization in the Izu Peninsula during the beginning of lithospheric extension is similar to that of the Sado Au–Ag deposit on Sado island in the Japan Sea. Two mineralization events coincide with extensive tholeiitic mafic volcanism and injections of dyke swarms related to the back‐arc opening of the Japan Sea. The geological setting of the Au–Ag mineralization in Izu and Sado is also similar to that of the epithermal Au–Ag deposits in northern Nevada, where mineralization was contemporaneous with crustal extension and tholeiitic mafic magmatism derived from the asthenospheric mantle. This study suggests that epithermal Au mineralization at shallow crustal depths is a product of large‐scale lithospheric evolution.  相似文献   

The impact of the Wangara experiment   总被引：1，自引：0，他引：1  

G. D. Hess  B. B. Hicks  Tetsuji Yamada 《Boundary-Layer Meteorology》1981,20(2):135-174

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Random response analysis of a non-linear soil-suspension bridge pier     

Y. Yamada  H. Takemiya  K. Kawano 《地震工程与结构动力学》1979,7(1):31-47

The structure analysed herein is a tower and pier system of a long-span suspension bridge. The tower shaft is modelled to allow classical normal modes decomposition in order to reduce higher modes. The pier is assumed to be rigid body free to translation as well as to rocking motion, being reacted by the surrounding soil compliance that is derived from a continuum mechanics approach. Linear and non-linear soil and structural dynamic interaction is dealt with by random vibration theory with use of the linearization technique and complex modal analysis. Primary interest is placed on the investigation of the dynamic characteristics of the total interaction system and the rms response with change of the soil condition and input excitation level. Also discussed is the approximate response analysis, using classical normal modes for the interaction system, for purposes of practical design.  相似文献   

PBL similarity profiles determined from a level-2 turbulence-closure model     

Tetsuji Yamada 《Boundary-Layer Meteorology》1979,17(3):333-351

A diagnostic model for the determination of similarity profiles of turbulence and mean-wind gradient in the planetary boundary layer is developed. Vertical profiles of a turbulence length scale and the flux Richardson number are formulated through the extension of the relationships for the constant flux layer. These profiles together with a turbulence energy equation and a similarity profile empirically determined for heat or momentum flux are used to compute the turbulence energy. Relationships previously derived from a turbulence closure model are used to compute second moments of turbulence.  相似文献   

Seismic damage estimation for low- and mid-rise buildings in japan     

C. Scawthorn  H. Iemura  Y. Yamada 《地震工程与结构动力学》1981,9(2):93-115

While much effort has been spent on analysis of individual structures, building class seismic damage estimators, of value in disaster planning, code-writing, city planning, national hazards policy formulation, etc., have been little investigated. Based largely on data from Sendai City, Japan in the 12 June, 1978 Miyagiken-oki earthquake (M_L = 7.4), estimators of seismic damage for low- and mid-rise buildings in urban Japan have been determined. For low-rise buildings, based on damage to over 60,000 buildings, damage ratios for onset of damage and collapse and for cost of damage are found to correlate best with response spectra at 0.75 s. Using published test data and average building properties, a seismic damage model explains the low-rise building behaviour and permits examination of the effect of structural changes on the estimated damage. For mid-rise buildings, damage states (0: none, 4: total) are determined as a function of maximum storey displacement, based on published natural period determinations (pre- and post-earthquake) for 189 mid-rise buildings in Sendai. The effects of structural changes on expected damage can also be estimated. With these two building class damage estimators, a large part of future seismic damage to urban Japan can be estimated, as well as the effects of various mitigation measures.  相似文献   

Contributions from mafic alkaline magmas to the Bingham porphyry Cu–Au–Mo deposit, Utah, USA   总被引：1，自引：0，他引：1  

Daniel T. Maughan  Jeffrey D. Keith  Eric H. Christiansen  Tamalyn Pulsipher  Keiko Hattori  Noreen J. Evans 《Mineralium Deposita》2002,37(1):14-37

The Bingham porphyry Cu-Au-Mo deposit, Utah, may only be world-class because of substantial contributions of sulfur and metals from mafic alkaline magma to an otherwise unremarkable calc-alkaline system. Volcanic mafic alkaline rocks in the district are enriched in Cr, Ni, and Ba as well as Cu, Au, platinum group elements (PGE), and S. The bulk of the volcanic section that is co-magmatic with ore-related porphyries is dacitic to trachytic in composition, but has inherited the geochemical signature of high Cr, Ni, and Ba from magma mixing with the mafic alkaline rocks. The volcanic section that most closely correlates in time with ore-related porphyries is very heterogeneous containing clasts of scoriaceous latite, latitic, and minette, and flows of melanephelinite, shoshonite, and olivine latite in addition to volumetrically dominant dacite/trachyte. Bingham ore-related porphyries show ample evidence of prior mixing with mafic alkaline magmas. Intrusive porphyries that have not been previously well-studied have several chemical and mineralogical indications of magma mixing. These "mixed" lithologies include the hybrid quartz monzonite porphyry, biotite porphyry, and minette dikes. Even some of the more silicic latite and monzonite porphyries retain high Cr and Ba contents indicative of mixing and contain trace amounts of sapphire (<1 mm). The heterogeneous block and ash flow deposits also contain sapphire and are permissively correlated with the intrusions based on chemical, mineralogical, and isotopic data. Magma mixing calculations suggest about 10% of the monzonitic/latitic ore-related magma may have been derived from mafic alkaline magma similar to the melanephelinite. If the original S content of the mafic magma was about 2,000-4,000 ppm, comparable with similar magmas, then the mafic magma may have been responsible for contributing more than half of the S and a significant portion of the Cu, Au, and PGE in the Bingham deposit.  相似文献   

Life Recovery of 1995 Kobe Earthquake Survivors in Nishinomiya City: A Total-Quality-Management-Based Assessment of Disadvantaged Populations     

Takeda  Joe  Tamura  Keiko  Tatsuki  Shigeo 《Natural Hazards》2003,29(3):567-585

The main objectives of this study were (1) to examine what has beenrecovered and what has not yet been recovered in Nishinomiya City five years after the GreatHanshin-Awaji Earthquake, and (2) to find current service needs for the earthquake survivors,especially for the disadvantaged populations. Disadvantaged populations are minorities in society, andtheir needs and opinions are often ignored and not reflected in the services or mitigation policy,despite the fact that they are the ones who are affected most by various hazards. At the same time, becauseof their unique characteristics and positions in society, their needs differ from the majorityof the society. Six hundred eighty-six opinion cards were collected in nine grassroots workshopsessions with various disadvantaged groups in Nishinomiya City, such as the physically challenged,the visually impaired, the elderly living in public housing, junior and senior high school students,mothers with small children, and those who lost their own homes because of the earthquake. Theseopinion cards were sorted out and analyzed by using a TQM(Total Quality Management)-basedassessment method. Since the TQM-based assessment method allows bottom-up integration ofopinions from each individual, it helps us identify unique needs of the disadvantaged groupsand reflect their opinions in mitigation plan and policies. The main findings of this study include (1)the city redevelopment cannot be achieved without integrating the viewpoints of thedisadvantaged; (2) the social support was a key resource for both mental health and community development;and (3) disaster experiences and adaptation produced civic mindedness among people in a community.  相似文献   

Estimation of water requirement per unit carbon fixed by Eucalyptus camaldulensis in semi-arid land of Western Australia     

T.Kojima  Y.Tanaka  S.Katoh  K.Tahara  N.Takahashi  K Yamada 《中国科学D辑(英文版)》2002,45(Z1)

Afforestation in arid land is a promising method for carbon fixation, but the effective utili-zation of water is highly important and required. Thus, the evaluation of the amount of water perunit carbon fixed with the tree growth is required to minimize the amount of water supplied to theplants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water andnutrients from roots, and CO2 as the carbon source from leaves with outflow of water vapor fromleaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutri-tional elements are dissolved in water flow in trees. They do not flow out by these reactions, butare accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluatethe water/carbon ratio. Assuming that nutrient concentration is constant in sap, and the differences in the ratios ofnutrient to carbon in living trees and dead (i.e. litter fall, etc.) are negiected, the ratio of the usedwater to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratioof nutrient to water in sap. However, some nutrients are translocated and concentrated within thetree and some may be discarded through litter fall. Thus it is important to examine which nutrientelement is the most suitable as the tracer. In this paper, the results of the above method applied to Eucalyptus camaldulensis in semi-arid land of Western Australia are shown. The value of water requirement per unit carbon fixationdetermined from potassium balance is between 421 kg-H2O/kg-C for mature trees and 285kg-H2O/k9-C for young trees, while the values from calcium balance are much larger than these.The cause of the discrepancy between these values is discussed based on the measured elementconcentrations in sap and trees and the plant physiology. Finally, the actual average value throughthe life of a tree is suggested to fall between the two values.  相似文献   

Volcanic Sequences Related to Kuroko Mineralization in the Hokuroku District, Northeast Japan     

Ryoichi Yamada  Takeyoshi Yoshida 《Resource Geology》2004,54(4):399-412

Abstract. Kuroko deposits are a representative volcanic‐hosted massive sulfide deposit and the Hokuroku district is economically the most important Kuroko containing province in Japan. There are two cycles of the bimodal volcanic sequence in the Hokuroku district. The pre‐ore volcanism started with basaltic activity and was followed by intensive felsic hyaloclas‐tic activity under bathyal conditions. The post‐ore sequence also began with basaltic activity intercalated with mudstone and was followed by alternating beds of pumice tuff with several lava flows and mudstone. Kuroko deposits are situated in the final period of the pre‐ore felsic volcanic sequence of the first bimodal volcanic cycle. Based on a detailed investigation of existing age data, it was concluded that the felsic volcanic sequences in the pre‐and post‐Kuroko formation can be divided into a pre‐ore dacite group (16–13.5 Ma), a D2 dacite group (lower unit of the post‐ore volcanic sequence, 12.7±0.6～ ll Ma) and a Dl dacite group (upper unit of the post‐ore sequence including quartz‐porphyry and granitoid, 11sim;10 Ma) in ascending order. Field and microscopic observations show that the pre‐ore dacite is characterized by aphyric to plagioclase‐phyric lava and the post‐ore dacitic rocks are characterized by quartz‐plagioclase‐phyric aphanitic lava and dome. These three dacite groups are petrochemically discriminated by SiO₂‐Al₂O₃ and CaO‐TiO₂ diagrams, excluding altered specimens. The distribution of the normative compositions on the Q‐An‐Ab‐Or diagram suggests that the pre‐ore dacites trend on the 5 kb cotectic line (equilibrated to 10—15 km deep) and those of the post‐ore trend along the 1 kb line (a few km deep). The secular variation of the major elements indicates that the rhyolitic members genetically related to the Kuroko formation could be the most differentiated products in the pre‐ore felsic volcanism. The distribution of Nb against SiO₂ content in the pre‐ and post‐ore bimodal volcanic cycles indicates that these two volcanisms could have been generated by different magmatic origins. The difference would have been caused by the tectonic conversion from a back‐arc to an island‐arc setting.  相似文献   

First Report of Sapphirine+Quartz Assemblage from Southern India: Implications for Ultrahigh-temperature Metamorphism   总被引：1，自引：0，他引：1  

Keiko Tateishi  Toshiaki Tsunogae  M. Santosh  A.S. Janardhan 《Gondwana Research》2004,7(4):899-912

We report here for the first time, the occurrence of sapphirine+quartz assemblage in textural equilibrium from quartzo-feldspathic and pelitic granulites from southern India. The sapphirine-bearing rocks occur as layered gneisses associated with pink granite within massive charnockite in Rajapalaiyam area in the southern part of Madurai Block. Sapphirine occurs in three associations: (i) fine-grained subhedral mineral associated with quartz enclosed in garnet, (ii) intergrowth with Al-rich orthopyroxene (up to 9.7 wt.% Al₂O₃), and (iii) in symplectitic intergrowth with orthopyroxene (Al₂O₃= 5.9–6.7 wt.%) and cordierite surrounding garnet. The sapphirine in association with quartz is slightly magnesian (X_Mg = 0.79–0.80) and low in Si content (1.55–1.56 pfu) as compared with those associated with orthopyroxene and cordierite (X_Mg= 0.77–0.79, Si = 1.59–1.63 pfu). The sapphirine+quartz assemblage suggests that the granulites underwent T>1050 °C peak metamorphism. Cores of porphyroblastic orthopyroxene in the sapphirine-bearing rocks shows high-Al₂O₃ content of up to 9.7 wt.%, suggesting T = 1040–1060°C and P = 8 kbar. FMAS reaction of sapphirine+quartz→garnet+sillimanite+cordierite indicates a cooling from sapphirine+quartz stability field after the peak ultrahigh-temperature metamorphism. Slightly lower temperature estimates from ternary feldspar and sapphirine-spinel geothermometers (T = 950–1000°C) also support a post-peak isobaric cooling. Corona textures of orthopyroxene+cordierite (±sapphirine), orthopyroxene+sapphirine, and cordierite+spinel around garnet suggest subsequent decompression. The sapphirine-quartz association and related textures reported in this study have important bearing on the ultrahigh-temperature metamorphism and exhumation history of the Madurai Block as well as on the tectonic evolution of the continental deep crust in southern India.  相似文献