Pyroxenes in the system Mg₂Si₂O₆-CaMgSi₂O₆ at high pressure     

Takeshi Mori  David H. Green 《Earth and Planetary Science Letters》1975,26(3):277-286

The enstatite-diopside solvus in the system Mg₂Si₂O₆-CaMgSi₂O₆ has been experimentally determined within the pressure range 5–40 kbars and the temperature range 900–1500°C. Experiments involving reversal of the phase boundaries by unmixing from glass starting material and by reaction of pure clinoenstatite and diopside showed difficulty in achieving equilibration due to persistence of metastable, subcalcic clinopyroxene and to the sluggishness of reaction rate. The experimental data showed that the temperature dependence of the diopside limb is less than previously accepted. At 1500°C and 30 kbars subcalcic diopside found by Davis and Boyd (1966) is shown to be metastable with respect to enstatite and more calcic diopside of composition En_42.3Di_57.7. The solvus widens with increasing pressure between 5 and 40 kbars at 1200°C, but at 900°C the pressure effect on the solvus is very small. The stability relationships of the four pyroxenes, protoenstatite, enstatite, iron-free pigeonite and diopside are summarized, based on data from the literature and the present study.  相似文献   

Early Permian ammonoids from the Kaeng Krachan Group of the Phatthalung-Hat Yai area, southern peninsular Thailand   总被引：1，自引：1，他引：1  

Masayuki Fujikawa  Katsumi Ueno  Apsorn Sardsud  Wirote Saengsrichan  Yoshihito Kamata  Ken-ichiro Hisada 《Journal of Asian Earth Sciences》2005,24(6):739

An Early Permian small ammonoid fauna consisting of Neocrimites sp., Agathiceras suessi Gemmellaro, A. girtyi Böse, Agathiceras? sp., and Miklukhoceras sp. was found in nodules of a fine sandstone bed exposed in the Phatthalung-Hat Yai area of southern peninsular Thailand. The ammonoid-bearing bed belongs stratigraphically to the uppermost part of the Kaeng Krachan Group, which is essentially a clastic-dominant, Late Carboniferous (?) to Early Permian stratigraphic unit, widely distributed in western and peninsular Thailand. This ammonoid fauna is considered to be of Bolorian (Kungurian) age and includes Agathiceras girtyi Böse, which is described for the first time from Thailand. The present discovery of Bolorian ammonoids suggests that the uppermost part of the Kaeng Krachan Group is slightly younger than previously considered and around the latest Early Permian. This further implies that the continental margin environment of the Sibumasu Block drastically changed at around Bolorian time from a cool, clastic-dominant shelf condition to a temperate to subtropical, carbonate platform due to rapid northward drift after middle Artinskian rifting.  相似文献   

Stability and P–V–T equation of state of KAlSi3O8-hollandite determined by in situ X-ray observations and implications for dynamics of subducted continental crust material     

Norimasa Nishiyama  Robert Paul Rapp  Tetsuo Irifune  Takeshi Sanehira  Daisuke Yamazaki  Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2005,32(8-9):627-637

In situ X-ray diffraction measurements of KAlSi₃O₈-hollandite (K-hollandite) were performed at pressures of 15–27 GPa and temperatures of 300–1,800 K using a Kawai-type apparatus. Unit-cell volumes obtained at various pressure and temperature conditions in a series of measurements were fitted to the high-temperature Birch-Murnaghan equation of state and a complete set of thermoelastic parameters was obtained with an assumed K′_300,0=4. The determined parameters are V _300,0=237.6(2) Å³, K _300,0=183(3) GPa, (?K _T,0/?T) _P =?0.033(2) GPa K^?1, a ₀=3.32(5)×10^?5 K^?1, and b ₀=1.09(1)×10^?8 K^?2, where a ₀ and b ₀ are coefficients describing the zero-pressure thermal expansion: α _T,0 = a ₀ + b ₀ T. We observed broadening and splitting of diffraction peaks of K-hollandite at pressures of 20–23 GPa and temperatures of 300–1,000 K. We attribute this to the phase transitions from hollandite to hollandite II that is an unquenchable high-pressure phase recently found. We determined the phase boundary to be P (GPa)=16.6 + 0.007 T (K). Using the equation of state parameters of K-hollandite determined in the present study, we calculated a density profile of a hypothetical continental crust (HCC), which consists only of K-hollandite, majorite garnet, and stishovite with 1:1:1 ratio in volume. Density of HCC is higher than the surrounding mantle by about 0.2 g cm^?3 in the mantle transition zone while this relation is reversed below 660-km depth and HCC becomes less dense than the surrounding mantle by about 0.15 g cm^?3 in the uppermost lower mantle. Thus the 660-km seismic discontinuity can be a barrier to prevent the transportation of subducted continental crust materials to the lower mantle and the subducted continental crust may reside at the bottom of the mantle transition zone.  相似文献   

Interactions of uranium with bacteria and kaolinite clay     

Toshihiko Ohnuki  Takahiro Yoshida  Takuo Ozaki  Mohamad Samadfam  Naofumi Kozai  Kunio Yubuta  Toshiaki Mitsugashira  Takeshi Kasama  Arokiasamy J. Francis 《Chemical Geology》2005,220(3-4):237-243

We assessed the accumulation of uranium (VI) by a bacterium, Bacillus subtilis, suspended in a slurry of kaolinite clay, to elucidate the role of microbes on the mobility of U(VI). Various mixtures of bacteria and the koalinite were exposed to solutions of 8 × 10^− 6 M- and 4 × 10^− 4 M-U(VI) in 0.01 M NaCl at pH 4.7. After 48 h, the mixtures were separated from the solutions by centrifugation, and treated with a 1 M CH₃COOK for 24 h to determine the associations of U within the mixture. The mixture exposed to 4 × 10^− 4 M U was analyzed by transmission electron microscope (TEM) equipped with EDS. The accumulation of U by the mixture increased with an increase in the amount of B. subtilis cells present at both U concentrations. Treatment of kaolinite with CH₃COOK, removed approximately 80% of the associated uranium. However, in the presence of B. subtilis the amount of U removed was much less. TEM–EDS analysis confirmed that most of the U removed from solution was associated with B. subtilis. XANES analysis of the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both revealed that it was present as U(VI). These results suggest that the bacteria have a higher affinity for U than the kaolinite clay mineral under the experimental conditions tested, and that they can immobilize significant amount of uranium.  相似文献   

Fluctuation in proteinaceous labile organic matter verified with degradation rate constants of terrestrial biochemical indicators     

Junya Kudo  Kensei Kobayashi  Katsumi Marumo  Yoshinori Takano   《Organic Geochemistry》2006,37(12):1655

Biogenic amino acids, taken as representative of organic matter, were analyzed to determine the apparent degradation rate constant in boreal terrestrial sediment. Age determination using ¹⁴C dating gave two rate constants: the initial degradation rate constant for glycine (k_{GLY 1}), the simplest amino acid, was 1.5 × 10⁻³ yr⁻¹ (r = 0.97) until about 2200 yr BP. After the inflection point, the rate constant k_{GLY 2} was 9.1 × 10⁻⁵ yr⁻¹ (r = 0.73). The degradation of amino acids in the labile organic matter in the sediment was markedly affected by rapid processes. After the inflection point, the rate constant profiles for sub-surface amino acids were shown to have discontinuous relationships with sediment age. One pattern which emerged in the vertical distribution is that the biogenic amino acid degradation rate constant k was far greater in the labile organic matter phase than that in the refractory organic matter over the past 10,000 years.  相似文献   

Collision structure in the upper crust beneath the southwestern foot of the Hidaka Mountains, Hokkaido, Japan as derived from explosion seismic observations     

Takeo Moriya  Hiroshi Okada  Takeshi Matsushima  Shuzo Asano  Toshikatsu Yoshii  Akira Ikami   《Tectonophysics》1998,290(3-4):181-196

The P-wave velocity structure of the upper crust beneath a profile ranging from Niikappu to Samani in the southwestern foot of the Hidaka Mountains, Hokkaido, Japan was obtained through analysis of refraction and wide-angle reflection data. The mountains are characterized by high seismicity and a large gravity anomaly. The present profile crosses the source region of the 1982 Urakawa-oki earthquake (M_s 6.8). The length of the profile is 66 km striking northwest and southeast. Along the profile, 64 vertical geophones were set up and 5 shot points were chosen. For each shot, a 400–600 kg charge of dynamite was detonated. The studied area is composed of four major geological belts: Neogene sedimentary rocks, the Kamuikotan belt, the Yezo Group, and the Hidaka belt. The measurement line crosses these geological trend at an oblique angle. The structure obtained is characterized by remarkable velocity variations in the lateral direction and reflects the surface geological characteristics. A thin, high-velocity layer (HVL) was found between low-velocity materials in the central part of the profile, beneath the Kamuikotan Metamorphic Belt, at a depth ranging from 0.5 to 6 km, overthrusting toward the west on the low-velocity materials consisting of Neogene sedimentary rocks, and forming gentle folds. Outlines of the velocity structure of the Hidaka Mountains yielded by other studies have shown a large-scale overthrust structure associated with the collision of the Outer Kurile and the Outer Northern Honshu Arcs. The shallow velocity structure inferred by the present study showed a similar (although small scale) overthrust structure. The obtained structure shows that the composite tectonic force, comprising westward movement of the Outer Kurile Arc and northward movement of the Outer Northern Honshu Arc, plays an important role in the evolution of the tectonic features of the crust and upper mantle in a wide depth range beneath the Hidaka Mountains.  相似文献   

Observational tests of x-matter models     

Takeshi Chiba  Naoshi Sugiyama  & Takashi Nakamura 《Monthly notices of the Royal Astronomical Society》1998,301(1):72-80

We study gravitational lensing statistics, matter power spectra and the angular power spectra of the cosmic microwave background (CMB) radiation in x-matter models. We adopt an equation of state of x-matter which can express a wide range of matter from pressureless dust to the cosmological constant. A new ingredient in this model is the sound speed of the x-component, in addition to the equation of state w ₀ =  p _x0/ρ_x0. Except for the cosmological constant case, the perturbations of x-matter itself are considered. Our primary interest is in the effect of non-zero sound speed on the structure formation and the CMB spectra. It is found that there exist parameter ranges where x-matter models are consistent with all current observations. The x-matter generally leaves imprints in the CMB anisotropy and the matter power spectrum, which should be detectable in future observations.  相似文献   

Thermal structure and uplift of the Cretaceous Shimanto Belt, Kii Peninsula, Southwest Japan: An illite crystallinity and Mite b_o, lattice spacing study     

M. Aslam  Awan Katsumi  Imura 《Island Arc》1996,5(1):69-88

Abstract Illite crystallinity (IC) and illite b, lattice spacing were measured across the Cretaceous Shimanto Belt, Kii Peninsula, Southwest Japan. For the IC survey, 103 samples of argillaceous rocks were analyzed from the central area and the western area of the belt. Values of IC (Kubler Index) vary between 0.28 and 0.71 Δ°2θ and indicate diagenetic and anchizone metamorphism respectively. The IC distribution reveals two contrasting patterns of thermal maturity. The Hanazono Formation, exposed in the northern area of the belt, generally dips north, but IC values increase systematically from 0.28 Δ°2θ in the north to 0.54 Δ°2θ in the south and indicate an inverted thermal structure. Values in other formations vary widely in the southern area of the belt ranging between 0.45 and 0.71 Δ°2θ, but the values do not show any systematic change from north to south and on average remain almost constant. Illite b_o, lattice spacing values for 56 samples vary between 9.006 and 9.041 Å corresponding to intermediate pressure conditions of the metamorphic facies. These values, combined with paleotemperatures estimated from IC, indicate paleogeothermal gradients of 22 and 31°C/km for the northern and southern areas of the belt, respectively. The inverted thermal structure of the Hanazono Formation, together with a lower paleogeothermal gradient, possibly is a result of the subduction of a relatively cold oceanic plate during the Late Cretaceous. The higher geothermal gradient could be a product of late thermal overprinting caused by the later subduction of a comparatively younger and hotter oceanic plate during the Eocene.  相似文献   

Irrigation related arsenic contamination of a thin,alluvial aquifer,Madison River Valley,Montana, U.S.A.     

John L. Sonderegger  Takeshi Ohguchi 《Environmental Geology》1988,11(2):153-161

The arsenic concentration in 13 water samples from wells in the thin, alluvial aquifer of the Madison River Valley, Montana, U.S.A. ranged from 26 to 150 μg/l. The Madison River, which originates in Yellowstone National Park, has a mean arsenic concentration of 51 μg/l (σ=26 μg/l), based upon very limited sampling in the study area during the main irrigation period. Groundwater arsenic concentration increases down the valley can be best correlated with the intensity of ditch irrigation in this semiarid area. No other sources of dissolved arsenic as concentrated as that of the river water have been identified. Evaporative concentration of river-derived irrigation water is believed to have been the overwhelming factor in the contamination of this shallow aquifer.  相似文献   

Iron oxidation state of a 2.45-Byr-old paleosol developed on mafic volcanics     

Satoshi Utsunomiya  Takashi Murakami  Takeshi Kasama 《Geochimica et cosmochimica acta》2003,67(2):213-221

The 2.45-Byr-old weathering profile developed on early Proterozoic mafic volcanics located near Cooper Lake, Ontario, Canada, was examined geochemically and mineralogically for a better understanding of the atmospheric oxygen evolution. Ferrous to ferric ion, Fe(II) and Fe(III), respectively, ratios of the bulk rock samples were analyzed by Mössbauer spectrometry. The total Fe (Fe(T)) and Fe(II) concentrations decrease from 12.0 and 11.2 wt.% to 1.85 and 0.89 wt.%, respectively, from the bottom to the top of the weathering profile. The Fe(T) and Fe(II) concentrations normalized to Ti and Zr, as well as the Fe(II)/Fe(III) ratio of raw data, linearly decrease with depth toward the top, while the Fe(III) concentration remains nearly constant throughout the profile. The linear decrease of Fe(II), accompanied by the nearly constant distribution of Fe(III), is difficult to be explained by the scenario of oxidizing weathering and subsequent reducing hydrothermal alteration. The behaviors of Fe(II) and Fe(III) can be simply explained by anoxic weathering. The anoxic weathering suggests that the 2.45-Ga atmosphere was anoxic. The slight increase of Fe/(Fe+Mg) in the octahedral sites of chlorite toward the top and no Ce anomaly in the REE patterns are also consistent with anoxic weathering.  相似文献