Off-scraped Permian-Jurassic bedded chert thrust on Jurassic-early Cretaceous accretionary prism: Radiolarian evidence from le Island, central Ryukyu Island Arc     

Gaoping  Shen  Hiroshi  Ujilé Katsuo  Sashida 《Island Arc》1996,5(2):156-165

Abstract The pre-Neogene basement of the central Ryukyu Island Arc shows zonal structures analogous to those of the outer belt of southwest Japan. The innermost terrane (Iheya Zone) consists of isoclinally folded beds dipping northwestward; the anticlinal cores are composed mainly of Permian chert, whereas the synclinal parts are represented by Jurassic to Cretaceous sandstone-rich alternating siliceous shale and chert, bearing appropriate radiolarian fossils. At the east-central area of Ie Island, the basement rocks are exposed as a 172 m high peak, Tattyu. The flank area of Tattyu is composed of latest Jurassic to Berriasian siliceous shale and chert as part of an accretionary prism, while most of Tattyu is composed of a continuous and very compact sequence of Norian through Kimmeridgian (?) bedded chert which is rather gently inclined. Beyond an unexposed part below the Norian chert, Guadalupian chert is recognized. It is inferred that this pelagic chert (Tattyu sequence) was off-scraped and thrust on to the accretionary prism which developed on its flank area in an accretion process after the Early Cretaceous.  相似文献   

Pre-accretionary mineralization of Japan     

Kohei  Sato Katsuo  Kase 《Island Arc》1996,5(3):216-228

Abstract The metallogeny of Japan can be grouped into four environments: (1) Paleozoic-Mesozoic stratiform Cu and Mn deposits within accretionary complexes, (2) Cretaceous-Paleogene post-accretionary deposits related to felsic magmatism in a continental-margin are environment, (3) Miocene epigenetic and syngenetic deposits related to felsic magmatism during back-arc opening, and (4) late Miocene-Quaternary volcanogenic deposits in an island-are environment. Group (1) deposits were a major source of Cu and Mn for the Japanese mining industry, and this style of mineralization is reviewed here. The stratiform Cu and Mn deposits were formed on the sea floor during the late Paleozoic to Mesozoic, and were subsequently accreted to active continental margins mainly in Jurassic to Cretaceous age. The Cu sulfide deposits, termed Besshi type, are classified into two subtypes: the Besshi-subtype deposit is related to basaltic volcanism, probably at a mid-oceanic ridge or rise; the Hitachi subtype is related to bimodal volcanism, probably in a back-arc or continental rift. Most of the Besshisubtype deposits occur in the Sanbagawa metamorphic belt, with some occurrences in weakly metamorphosed Jurassic and Cretaceous accretionary terrains. This subtype is divided into two groups: the sediment-barren group is hosted by basalt-chert sequences; whereas the sedimentcovered group is hosted by basalt-shale sequences. Both subtypes are characterized by S isotope trends similar to those of sea-floor sulfide deposits now forming at mid-oceanic ridges. The Hitachi-subtype deposits occur in late Paleozoic volcanic-sedimentary sequences and lack pelagic sediments. These deposits are characterized by association of sphalerite- and barite-rich ores. The Mn deposits occur mainly in Middle Jurassic to Early Cretaceous accretionary complexes containing abundant chert beds of Triassic to Jurassic age. Their locations are well separated from those of the Cu sulfide deposits. The Mn deposits are divided into two types: the Mn type, hosted by chert, and the Fe-Mn type, sandwiched between chert and basaltic volcanic rocks. The Mn-type ores appear to have deposited on the deep-sea floor further from the site of hydrothermal activity than the Fe-Mn type. Primary Mn precipitates may have been transformed to rhodochrosite and other Mn-minerals during diagenesis. Many of the Mn deposits were significantly metamorphosed during intrusion of Cretaceous granitoids, resulting in a very complex mineralogy.  相似文献   

Intensity oscillation in Hα-fine structure     

Arvind Bhatnagar  Katsuo Tanaka 《Solar physics》1972,24(1):87-97

Using a new technique of directly measuring the intensity variation from the 16 mm time-lapse filtergram movies taken in the blue wing and in the line center of H, we found periodic intensity oscillations in the center of H-supergranulation network, in rosette centers and in plage granules. The oscillatory period of intensity in the network is of the order of 170 ± 44 seconds while in regions of stronger magnetic field, such as in plages and in rosettes, the period was found to be longer, on the order of 300 ± 50 seconds. It is suggested that observed intensity oscillation in the rosette center is related to the shooting out of dark mottles from rosettes. Oscillatory intensity fluctuations have been also observed in the sunspot umbra.  相似文献   

Spatial distribution,sources and risk assessment of potentially toxic trace elements and rare earth elements in soils of the Langtang Himalaya,Nepal     

Lekhendra Tripathee  Shichang Kang  Dipesh Rupakheti  Qianggong Zhang  Roshan Man Bajracharya  Chhatra Mani Sharma  Jie Huang  Ayush Gyawali  Rukumesh Paudyal  Mika Sillanpää 《Environmental Earth Sciences》2016,75(19):1332

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Ore Mineralogy and Mineral Chemistry of the Ashanti Gold Deposit at Obuasi, Ghana     

Shiloh OSAE  Katsuo KASE  Masahiro YAMAMOTO 《Resource Geology》1999,49(1):1-11

Abstract: The gold deposit at Ashanti occurs in the Proterozoic Birimian formation of Ghana. Two main ore types mined from the deposit are gold-bearing quartz veins, and gold-sulfide disseminations in metasediments and metavolcanics. The main sulfide minerals in the gold-sulfide disseminated ores are arsenopyrite, pyrite and pyrrhotite, and to a very minor extent, sphalerite and tetrahedrite. Carbonate alteration and sericitization are prominent in the metavolcanics and the metasediments, respectively. In the quartz veins, pyrite and arsenopyrite commonly occur in small amounts, but gold mostly occurs in contact with tetrahedrite, chalcopyrite, galena, aurostibite, and sphalerite. Pyrrhotite is absent in the quartz veins.
Microprobe studies indicate that As content of homogeneous arsenopyrite grains ranges from 27. 0 to 31. 7 atm%, and gives mineralization temperatures from 170 to 430°C, although mostly from 300 to 400°C. Chlorite geothermometry using temperature dependence of substitution of Al for Si in the tetrahedral site gives formation temeratures of 330 to 400°C, comparable to the arsenopyrite temperatures. Applying sphalerite–pyrite–pyrrhotite geobarometry to sphalerite with FeS contents from 13. 6 to 12. 5 mol%, the pressure was estimated to be in a range from 5. 9 to 7. 0 kb at the stage of elevated temperatures.
Mineralogical observations, especially absence of pyrrhotite in the quartz veins, together with microprobe data for gold and associated minerals suggest that the fluids having ascended through fissures in the Ashanti deposit were reduced by the reaction with carbonaceous materials in the metasediments during the declining stage of the regional metamorphism.  相似文献   

Modelling Wet and Dry Spells with Mixture Distributions   总被引：1，自引：0，他引：1  

I. Dobi-Wantuch  J. Mika  L. Szeidl 《Meteorology and Atmospheric Physics》2000,73(3-4):245-256

Summary The object of the study is to develop a discrete precipitation model which is able to simulate local, daily series of precipitation occurrences. The model is fitted to the observed data of two stations, Szeged and Szombathely, in Hungary (1951–1995), with pronounced attention to the reproduction of long dry periods, as characteristic features of the climate in Central Europe. The point of the approach is to model the duration of consecutive dry and wet series, i.e., spells, instead of individual wet or dry days. After having comparisons of three different aspects performed, the selected precipitation threshold is 0.1 mm. This threshold keeps the duration of dry and wet periods more or less balanced, whereas the value of the threshold does not fundamentally influence either the conditional distribution of macrocirculation types or the local weather statistics related to the so defined wet or dry days. The duration of both wet and dry spells are found to be independent of the length of either the preceding (opposite) or the last, but one (identical) state. It is also demonstrated that mixed distributions fairly fit to the wet and dry spells, whereas the simple geometric does not, especially due to the erroneous lack of long dry sequences. Weighted sum of two geometric distributions, as well as that of one geometric and one Poisson distribution exhibits good fitting for the dry spells, whereas only the latter one can be advised to employ for the wet periods. Parameters of the distributions obviously depend on the season and the site, in question. Received June 30, 1999 Revised February 3, 2000  相似文献   

Lithostratigraphy of Permian marine sequences, Khao Pun Area, central Thailand: Paleoenvironments and tectonic history     

Vichai Chutakositkanon  Punya Charusiri and  Katsuo Sashida 《Island Arc》2000,9(2):173-187

Geologic mapping and subsurface lithostratigraphic investigations were carried out in the Khao Pun area (4 km²), central Thailand. More than 250 hand specimens, 70 rock slabs, and 70 thin sections were studied in conjunction with geochemical data in order to elucidate paleoenvironments and tectonic setting of the Permian marine sedimentary sequences. This sedimentary succession (2485 m thick) was re‐accessed and re‐grouped into three lithostratigraphic units, namely, in ascending order, the Phu Phe, Khao Sung and Khao Pun Formations. The Lower to lower Upper Permian sedimentary facies indicated the transgressive/regressive succession of shelf sea/platform environment to pelagic or abyssal environment below the carbonate compensation depth. The sedimentological and paleontological aspects, together with petrochemical and lithological points of view, reveal that the oldest unit might indicate an Early Permian sheltered shallow or lagoonal environment. Then the depositional basin became deeper, as suggested by the prolonged occurrence of bedded chert‐limestone intercalation with the local exposure of shallower carbonate build‐up. Following this, the depositional environment changed to pelagic deposition, as indicated by laminated radiolarian (e.g. Follicucullus sp.) cherts. This cryptic evidence might indicate the abyssal environment during middle Middle to early Late Permian; whereas, previous studies advocated shelf‐facies environments. Following this, the depositional condition might be a major regression on the microcontinent close to Indochina, from the minor transgressive/regressive cycles that developed within a skeletal barrier, and through the lagoon with limited circulational and anaerobic conditions, on to the tidal flat to the sheltered lagoon without effective land‐derived sediments.  相似文献   

Nickel–bearing Djerfisherite in Gehlenite-Spurrite Skarn at Kushiro, Hiroshima Prefecture, Japan     

Yasushi TAKECHI  Isao KUSACHI  Yoshihiro NAKAMUTA  Katsuo KASE 《Resource Geology》2000,50(3):179-184

Abstract: Djerfisherite occurs intimately intergrown with troilite and pentlandite in gehlenite-spurrite skarn at Kushiro, mainly as inclusions in gehlenite and andradite grains. The mode of occurrence indicates that the djerfisherite formed in the culminated stage of the contact metamorphic-metasomatic process. The chemical compositions of the mineral are approximately represented by a formula of K₆Na(Fe, Ni, Cu)₂₄S₂₆Cl with Ni up to 4. 85. It is likely that high temperature condition corresponding to the formation of gehlenite-spurrite skarn as well as low f_O2 and f_S2 conditions are responsible for the formation of djerfisherite in the potassium-rich chemical environments.  相似文献   

Laboratory annealing experiments of refractory silicate grain analogs using differential scanning calorimetry     

Yuki KIMURA  Joseph A. NUTH III  Katsuo TSUKAMOTO  Chihiro KAITO 《Meteoritics & planetary science》2011,46(1):92-102

Abstract– Exothermic reactions during the annealing of laboratory synthesized amorphous magnesium‐bearing silicate particles used as grain analogs of cosmic dust were detected by differential scanning calorimetry (DSC) in air. With infrared spectroscopy and transmission electron microscopy, we show that cosmic dust could possibly undergo fusion to larger particles, with oxidation of magnesium silicide and crystallization of forsterite as exothermic reactions in the early solar system. The reactions begin at approximately 425, approximately 625, and approximately 1000 K, respectively, and the reaction energies (enthalpies) are at least 727, 4151, and 160.22 J g⁻¹, respectively. During the crystallization of forsterite particles, the spectral evolution of the 10 μm feature from amorphous to crystalline was observed to begin at lower temperature than the crystallization temperature of 1003 K. During spectral evolution at lower temperature, nucleation and/or the formation of nanocrystallites of forsterite at the surface of the grain analogs was observed.  相似文献   

Airborne remote sensing of spatiotemporal change (1955–2004) in indigenous and exotic forest cover in the Taita Hills,Kenya     

Petri K.E. Pellikka  Milla Lötjönen  Mika Siljander  Luc Lens 《International Journal of Applied Earth Observation and Geoinformation》2009

We studied changes in area and species composition of six indigenous forest fragments in the Taita Hills, Kenya using 1955 and 1995 aerial photography with 2004 airborne digital camera mosaics. The study area is part of Eastern Arc Mountains, a global biodiversity hot spot that boasts an outstanding diversity of flora and fauna and a high level of endemism. While a total of 260 ha (50%) of indigenous tropical cloud forest was lost to agriculture and bushland between 1955 and 2004, large-scale planting of exotic pines, eucalyptus, grevillea, black wattle and cypress on barren land during the same period resulted in a balanced total forest area. In the Taita Hills, like in other Afrotropical forests, indigenous forest loss may adversely affect ecosystem services.  相似文献