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151.
152.
Kenji Shimizu Takaaki Itai Minoru Kusakabe 《Geostandards and Geoanalytical Research》2006,30(2):121-129
A simple and accurate method to determine fluorine and chlorine contents in small amounts (∼ 30 mg) in rock has been developed using ion chromatography after extraction by alkaline fusion. Powdered sample was mixed with sodium carbonate and zinc oxide at a mass ratio of 1:3:1, and was fused in an electric furnace at 900 °C for 30-40 minutes. An aqueous solution obtained by dissolving the fused silicate rock was diluted to the appropriate concentration of sodium carbonate (< ∼ 24 mmol l-1 ) to minimise the tailing effect on F- during ion chromatography caused by the large amount of carbonate species originating from the flux. Fluorine and chlorine contents were then determined by a standard additions method. Based on the relative standard deviation of the backgrounds, detection limits of both fluorine and chlorine were ∼ 4 μg g-1 , when 30 mg test portions were fused and diluted by a factor of 1200. We also report new fluorine and chlorine contents in nine GSJ (Geological Survey of Japan) reference materials, including peridotite (JP-1), granite (JG-1a), basalts (JB-1b, 2 and 3), andesites (JA-1 and 2) and rhyolites (JR-1 and 2). Fluorine and chlorine contents in the reference materials in this study were consistent with previously reported values. Reproducibilities were < 10 % for samples with F and Cl concentrations of > 20 μg g-1 and < 20 % with F and Cl < 20 μg g-1 . 相似文献
153.
A monitoring GPS array recently developed in Japan can yield nationwide maps of active inland tectonic zones (ATZs) on a mesoscale, approximately 70 to several hundred kilometers in lateral extent. But it has been difficult to characterize ATZs in Japan, as they are in fact operational on multiple scales and our efforts are often hindered by various irregularities in the data. The key to overcoming these problems would be to gain an insight into the available data before any precise kinematic modeling is performed with indefinite assumptions. In this study, horizontal velocity fields, deduced from the nationwide GPS array, were treated with a set of techniques in robust smoothing and exploratory data analysis that brought out exceptionally powerful mesoscale ATZs, and made them easier to characterize. The resolved ATZs were then retrospectively monitored to study their regional and temporal variations, using a set of approx. 840 observation stations, about 30 km apart, for a 4-year series of fixed observation time-intervals, 810 days each. The smoothing operation involved three steps: (1) imputation of the velocity fields for the purpose of anti-aliasing, (2) robust smoothing of the velocity fields with the median operative, and (3) visualization of deformation-rate distributions in several coordinate independent parameters, and post-filtering. The geometrical resolvability of mesoscale ATZs was confirmed by calibrating the smoothing scheme against synthetic tectonic boundary models before it was applied to the case study in Japan. ATZs in Japan, which are essentially visible as systematic deviations in the velocity fields on the International Terrestrial Reference Frame (ITRF) and as strain rate anomalies, were highlighted sharply along some known tectonic zones, chains of active volcanoes, and areas above low seismic velocity anomalies in the crust and upper mantle, all of which generally paralleled the offshore trench axes. The geometrical agreements among the mapped ATZs and the physical anomalies in the crust are presumably due to their common structural weakness on the mesoscale. In the four main islands of Japan, all but 30–40% of the strain rate anomalies persisted during the entire 6 years of the case study period, while the rest sporadically appeared or disappeared in a period from several months to a few years. The transient shifts in the deformation rates were remarkably synchronous with some nearby major tectonic episodes: large earthquakes and slow events. Differential plate coupling strengths along the subduction zones can also be inferred from the persistent pattern of rotational strain rate anomalies forming clockwise and counterclockwise pairs along the Pacific. Our empirical observations suggest that the first-order features of interseismic crustal deformations in Japan can be characterized as collateral processes behaving in response to fluctuations of the tectonic stresses on multiple scales, likely influenced by changes of plate coupling strengths on the contiguous subduction faults. 相似文献
154.
We performed high-pressure experiments on the crystallization of water ice I and III in the ammonia-water (NH3)x(H2O)(1−x) system, and apply the results to the interiors of icy bodies in the Solar System. Phase equilibrium lines between an entirely liquid solution and a liquid solution in which water ice forms (liquidus lines) were determined for ammonia concentration by mass X equal to 0.034, 0.0472, 0.111, 0.176, and 0.229. Growth-melting of ice I as well as ice III crystals were observed. Application of the results to icy satellites that are potential bearers of ammonia shows that ammonia admixture decreases the depth of the liquidus surface. A shift of the liquidus temperature within a satellite depends on three parameters: the ammonia concentration, X; the temperature gradient, α; and the product of density and gravity, ρg. 相似文献
155.
Takashi Kudo Minoru Sasaki Yoshihiro Uchiyama Akifumi Nozawa Hisashi Sasaki Takeshi Tokizawa Shinji Takarada 《Island Arc》2007,16(1):133-155
Abstract The Hakkoda‐Towada caldera cluster (HTCC) is a typical Late Cenozoic caldera cluster located in the northern part of the Northeast Japan Arc. The HTCC consists of five caldera volcanoes, active between 3.5 Ma and present time. The felsic magmas can be classified into high‐K (HK‐) type and medium‐ to low‐K (MLK‐) type based on their whole‐rock chemistry. The HK‐type magmas are characterized by higher K2O and Rb contents and higher 87Sr/86Sr ratios than MLK‐type magmas. Both magmas cannot be derived from fractional crystallization of any basaltic magma in the HTCC. Assimilation‐fractional crystallization model calculations show that crustal assimilation is necessary for producing the felsic magmas, and HK‐type magmas are produced by higher degree of crustal assimilation with fractional crystallization than MLK‐type magmas. Although MLK‐type magmas were erupted throughout HTCC activity, HK‐type magmas were erupted only during the initial stage. The temporal variations of magma types suggest the large contribution of crustal components in the initial stage. A major volcanic hiatus of 3 my before the HTCC activity suggests a relatively cold crust in the initial stage. The cold crust probably promoted crustal assimilation and fractional crystallization, and caused the initial generation of HK‐type magmas. Subsequently, the repeated supply of mantle‐derived magmas raised temperature in the crust and formed relatively stable magma pathways. Such a later system produced MLK‐type magmas with lesser crustal components. The MLK‐type magmas are common and HK‐type magmas are exceptional during the Pliocene–Quaternary volcanism in the Northeast Japan Arc. This fact suggests that exceptional conditions are necessary for the production of HK‐type magmas. A relatively cold crust caused by a long volcanic hiatus (several million years) is considered as one of the probable conditions. Intensive crustal assimilation and fractional crystallization promoted by the cold crust may be necessary for the generation of highly evolved HK‐type felsic magmas. 相似文献
156.
Tetsuya Yokoyama Festus T. Aka Minoru Kusakabe 《Geochimica et cosmochimica acta》2007,71(7):1835-1854
Precise measurements of 238U-230Th-226Ra disequilibria in lavas erupted within the last 100 yr on Mt. Cameroon are presented, together with major and trace elements, and Sr-Nd-Pb isotope ratios, to unravel the source and processes of basaltic magmatism at intraplate tectonic settings. All samples possess 238U-230Th-226Ra disequilibria with 230Th (18-24%) and 226Ra (9-21%) excesses, and there exists a positive correlation in a (226Ra/230Th)-(230Th/238U) diagram. The extent of 238U-230Th-226Ra disequilibria is markedly different in lavas of individual eruption ages, although the (230Th/232Th) ratio is constant irrespective of eruption age. When U-series results are combined with Pb isotope ratios, negative correlations are observed in the (230Th/238U)-(206Pb/204Pb) and (226Ra/230Th)-(206Pb/204Pb) diagrams. Shallow magma chamber processes like magma mixing, fractional crystallization and wall rock assimilation do not account for the correlations. Crustal contamination is not the cause of the observed isotopic variations because continental crust is considered to have extremely different Pb isotope compositions and U/Th ratios. Melting of a chemically heterogeneous mantle might explain the Mt. Cameroon data, but dynamic melting under conditions of high DU and DU/DTh, long magma ascent time, or disequilibrium mineral/melt partitioning, is required. The most plausible scenario to produce the geochemical characteristics of Mt. Cameroon samples is the interaction of melt derived from the asthenospheric mantle with overlying sub-continental lithospheric mantle which has elevated U/Pb (>0.75) and Pb isotope ratios (206Pb/204Pb > 20.47) due to late Mesozoic metasomatism. 相似文献
157.
Yukinori Tani Kota Kurihara Fumiko Nara Nobuyasu Itoh Mitsuyuki Soma Yuko Soma Atsushi Tanaka Minoru Yoneda Masashi Hirota Yasuyuki Shibata 《Organic Geochemistry》2002,33(12)
Photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of Lake Baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial/post-glacial transition. The sedimentation age of the core spans the last 24 14C ka. Chlorophyll a, its derivatives, carotenoids and total organic carbon (TOC) started to increase after 15 14C ka, and the onset of biogenic silica occurred at 10 14C ka. This indicated that the post-glacial growth of diatoms was preceded by that of other phytoplankton groups. In the record of the pigments and TOC, a temporary decrease was observed in the period 11.5–10.5 14C ka, corresponding to the Younger Dryas cold period. The similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of TOC suggested the important contribution of fecal pellets to sedimentary organic matter in the lake. 相似文献
158.
159.
Ryutaro Sakai Minoru Kusakabe Masami Noto Teruaki Ishii 《Earth and Planetary Science Letters》1990,100(1-3)
Many serpentinite seamounts occur over a region 20–120 km west of the trench axis in the Izu-Ogasawara-Mariana forearc regions. The hydrogen and oxygen isotopic compositions of serpentine from these regions indicate that there are at least two kinds of waters responsible for serpentinization: seawater and water derived from dehydration of the descending slab. Serpentine from two Mariana and two Torishima samples with microscopically ductile and sheared texture (sheared-type) have lowerδD(−63to−52‰) and slightly higherδ18O values (+6.1 to +8.2‰) than that of other nine Ogasawara samples with mesh texture (mesh-type) (δD= −43to−49‰ andδ18O= +5.8to+6.7‰). This suggests that the sheared-type serpentine with lowerδD and slightly higherδ18O values was formed within the wedge mantle by interaction with water derived from a descending slab. The sheared texture is likely to have been produced during diapiric uplift. The unaltered portion of the ultramafic bodies later interacted with seawater after emplacement at or near the seafloor, resulting in formation of the mesh-type serpentine with higherδD values. 相似文献
160.
Oxygen isotope exchange between BaSO4 and H2O from 110 to 350°C was studied using 1 m H2SO4-1 m NaCl and 1 m NaCl solutions to recrystallize the barite. The slow exchange rate (only 7% exchange after 1 yr at 110°C and 91% exchange after 22 days at 350°C in 1 m NaCl solution) prompted the use of the partial equilibrium technique. However, runs at 300 and 350°C were checked by complete exchange experiments. The temperature calibration curve for the isotope exchange is calculated giving most weight to the high temperature runs where the partial equilibrium technique can be tested. Oxygen isotope fractionation factors (α) in 1 m NaCl solution (110–350°C), assuming a value of 1.0407 for αCO2H2O at 25°C, are: .These data, when corrected for ion hydration effects in solution (Truesdell, 1974), give the fractionation factors in pure water: .In the 1 m H2SO4-1 m NaCl runs, sulfur isotope fractionation between HSO?4 and BaSO4 is less than the detection limit of 0.4%. A barite-sulfide geothermometer is obtained by combining HSO?4H2S and sulfide-H2S calibration data.Barite in the Derbyshire ore field, U.K., appears to have precipitated in isotopic equilibrium with water and sulfur in the ore fluid at temperatures less than 150°C. At the Tui Mine, New Zealand, the barite-water geothermometer indicates temperatures of late stage mineralization in the range 100–200°C. A temperature of 350 ± 20°C is obtained from the barite-pyrite geothermometer at the Yauricocha copper deposit, Peru, and oxygen isotope analyses of the barite are consistent with a magmatic origin for the ore fluids. 相似文献