Petrographic features of a high-temperature granite just newly solidified magma at the Kakkonda geothermal field, Japan     

Munetake Sasaki  Koichiro Fujimoto  Takayuki Sawaki  Hitoshi Tsukamoto  Osamu Kato  Ryo Komatsu  Nobuo Doi  Masakatsu Sasada 《Journal of Volcanology and Geothermal Research》2003,121(3-4):247-269

A 3729-m-deep geothermal research well, WD-1a, provides us with a unique opportunity to study initial petrographic features of a high-temperature granite just after solidification of magma. The well succeeded in collecting three spot-cores of the Kakkonda Granite that is a pluton emplaced at a shallow depth and regarded as a heat source of the active Kakkonda geothermal system. The core samples were collected at the present formation temperatures of 370, 410 and over 500°C. These samples are granodiorite to tonalite consisting mainly of plagioclase, quartz, hornblende, biotite and K-feldspar. A sample collected at a formation temperature of over 500°C possesses the following remarkable petrographic features compared to the other two samples. Interstitial spaces are not completely sealed. K-feldspar exhibits no perthite by the exsolution of albite lamella. Quartz includes glassy melt inclusions without devitrification. Hornblende is less intensively altered to actinolite, and biotite is not altered. This study directly confirmed that perthite in K-feldspar is a recrystallization texture formed at 410–500°C based on a comparison of the in situ temperatures of the samples. Chemical compositions of minerals were analyzed to compare temperatures determined from geothermometers in several publications to the in situ temperatures of the samples.  相似文献   

Multifractal analysis of spatial distribution of microearthquakes in the Kanto region   总被引：5，自引：0，他引：5  

Takayuki Hirata  Masajiro Imoto 《Geophysical Journal International》1991,107(1):155-162

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The spatial distribution of earthquakes is a fractal, which is characterized by a fractal dimension. However, if a spatial distribution has a heterogeneous fractal structure, a single value of fractal dimension [e.g. D_o (capacity dimension) or D ₂ (correlation dimension)] is not enough to characterize it. From a multifractal viewpoint, we analysed the spatial distribution of microearthquakes in the Kanto region by using a local density function. Generalized dimensions, D_q , of the spatial distribution were calculated from the slopes of generalized correlation integrals, C_q(r) versus distance r , on a log-log plot, examining the self-similarity of the spatial distribution of microearthquakes. Self-similar structures are held well at scales from 1.26 to 12.6 km. Our results suggest that the spatial distribution of microearthquakes in the Kanto region is not a homogeneous fractal structure but a heterogeneous one with generalized dimensions D₂ = 2.2 ≤ D ₃≤…≤ D _∞= 1.7. The value of D _∞, the lower limit of fractal dimension, is the fractal dimension of the most intensive clustering in the heterogeneous fractal set. The fractal dimension of the most intensive clustering of microearthquakes in the Kanto region is 1.7.  相似文献   

Constraining atmospheric oxygen and seawater sulfate concentrations during Paleoproterozoic glaciation: In situ sulfur three-isotope microanalysis of pyrite from the Turee Creek Group, Western Australia     

Kenneth H. Williford  Martin J. Van Kranendonk  Takayuki Ushikubo  John W. Valley 《Geochimica et cosmochimica acta》2011,75(19):5686-5705

Previous efforts to constrain the timing of Paleoproterozoic atmospheric oxygenation have documented the disappearance of large, mass-independent sulfur isotope fractionation and an increase in mass-dependent sulfur isotope fractionation associated with multiple glaciations. At least one of these glacial events is preserved in diamictites of the ∼2.4 Ga Meteorite Bore Member of the Kungarra Formation, Turee Creek Group, Western Australia. Outcrop exposures of this unit show the transition from the Boolgeeda Iron Formation of the upper Hamersley Group into clastic, glaciomarine sedimentary rocks of the Turee Creek Group. Here we report in situ multiple sulfur isotope and elemental abundance measurements of sedimentary pyrite at high spatial resolution, as well as the occurrence of detrital pyrite in the Meteorite Bore Member. The 15.3‰ range of Δ³³S in one sample containing detrital pyrite (−3.6‰ to 11.7‰) is larger than previously reported worldwide, and there is evidence for mass-independent sulfur isotope fractionation in authigenic pyrite throughout the section (Δ³³S from −0.8‰ to 1.0‰). The 90‰ range in δ³⁴S observed (−45.5‰ to 46.4‰) strongly suggests microbial sulfate reduction under non-sulfate limiting conditions, indicating significant oxidative weathering of sulfides on the continents. Multiple generations of pyrite are preserved, typically represented by primary cores with low δ³⁴S (<−20‰) overgrown by euhedral rims with higher δ³⁴S (4-7‰) and enrichments in As, Ni, and Co. The preservation of extremely sharp sulfur isotope gradients (30‰/<4 μm) implies limited sulfur diffusion and provides time and temperature constraints on the metamorphic history of the Meteorite Bore Member. Together, these results suggest that the Meteorite Bore Member was deposited during the final stages of the “Great Oxidation Event,” when pO₂ first became sufficiently high to permit pervasive oxidative weathering of continental sulfides, yet remained low enough to permit the production and preservation of mass-independent sulfur isotope fractionation.  相似文献   

SIMS analyses of silicon and oxygen isotope ratios for quartz from Archean and Paleoproterozoic banded iron formations   总被引：1，自引：0，他引：1  

Philipp R. Heck  Jason M. Huberty  Takayuki Ushikubo  John W. Valley 《Geochimica et cosmochimica acta》2011,75(20):5879-5891

Banded iron formations (BIFs) are chemical marine sediments dominantly composed of alternating iron-rich (oxide, carbonate, sulfide) and silicon-rich (chert, jasper) layers. Isotope ratios of iron, carbon, and sulfur in BIF iron-bearing minerals are biosignatures that reflect microbial cycling for these elements in BIFs. While much attention has focused on iron, banded iron formations are equally banded silica formations. Thus, silicon isotope ratios for quartz can provide insight on the sources and cycling of silicon in BIFs. BIFs are banded by definition, and microlaminae, or sub-mm banding, are characteristic of many BIFs. In situ microanalysis including secondary ion mass spectrometry is well-suited for analyzing such small features. In this study we used a CAMECA IMS-1280 ion microprobe to obtain highly accurate (±0.3‰) and spatially resolved (∼10 μm spot size) analyses of silicon and oxygen isotope ratios for quartz from several well known BIFs: Isua, southwest Greenland (∼3.8 Ga); Hamersley Group, Western Australia (∼2.5 Ga); Transvaal Group, South Africa (∼2.5 Ga); and Biwabik Iron Formation, Minnesota, USA (∼1.9 Ga). Values of δ¹⁸O range from +7.9‰ to +27.5‰ and include the highest reported δ¹⁸O values for BIF quartz. Values of δ³⁰Si have a range of ∼5‰ from −3.7‰ to +1.2‰ and extend to the lowest δ³⁰Si values for Precambrian cherts. Isua BIF samples are homogeneous in δ¹⁸O to ±0.3‰ at mm- to cm-scale, but are heterogeneous in δ³⁰Si up to 3‰, similar to the range in δ³⁰Si found in BIFs that have not experienced high temperature metamorphism (up to 300 °C). Values of δ³⁰Si for quartz are homogeneous to ±0.3‰ in individual sub-mm laminae, but vary by up to 3‰ between multiple laminae over mm-to-cm of vertical banding. The scale of exchange for Si in quartz in BIFs is thus limited to the size of microlaminae, or less than ∼1 mm. We interpret differences in δ³⁰Si between microlaminae as preserved from primary deposition. Silicon in BIF quartz is mostly of marine hydrothermal origin (δ³⁰Si < −0.5‰) but silicon from continental weathering (δ³⁰Si ∼ 1‰) was an important source as early as 3.8 Ga.  相似文献   

Tracing depositional consequences of environmental radionuclides (137Cs and 210Pb) in Slovenian forest soils     

Ryoko Fujiyoshi  Takayuki Yamaguchi  Naoki Takekoshi  Kazumasa Okamoto  Takashi Sumiyoshi  Ivan Kobal  Janja Vaupotič 《Central European Journal of Geosciences》2011,3(3):291-301

Depth distribution profiles of environmental radionuclides (¹³⁷Cs and ²¹⁰Pb) have been investigated in soil to elucidate the underlying environment of semi-natural temperate deciduous and/or coniferous forest soils in Slovenia (?irovski vrh, Idrija, Ko?evski Rog, Pohorie, Gori?nica and Rakitna). Surface enrichment of both nuclides was observed at all the sites investigated in this study, suggesting that the soils had undergone little natural or anthropogenic disturbance for at least the last several decades. Apparent annual burial rates of ¹³⁷Cs (0.1–0.2 cm y^??1) were estimated to be about 1.3 times higher than those of ²¹⁰Pb at individual sites of different lithology, which suggests strong affinity of ²¹⁰Pb to soil organic matter. Variability of the vertical distribution profiles of these nuclides depends not only on “in situ” pedology but also on geographical and meteorological conditions, especially precipitation and wind direction.  相似文献   

Vegetation development and carbon storage on a glacier foreland in the High Arctic, Ny-Ålesund, Svalbard     

Shinpei Yoshitake  Masaki Uchida  Toshiyuki Ohtsuka  Hiroshi Kanda  Hiroshi Koizumi  Takayuki Nakatsubo 《Polar Science》2011,5(3):391-397

The distribution of organic carbon and its relationship to vegetation development were examined on a glacier foreland near Ny-Ålesund, Svalbard (79°N). In a 0.72-km² area, we established 43 study plots on three line transects along primary succession from recently deglaciated area to old well-vegetated area. At each plot, we measured the type and percent coverage of vegetation types. The organic carbon content of vegetation, organic soil, and mineral soil samples was determined based on their organic carbon concentration and bulk density. Cluster analysis based on vegetation coverage revealed five types of ground surfaces representing variations in the amounts and allocation patterns of organic carbon. In the later stages of succession, 7%–24% and 31%–40% of organic carbon was contained in the organic and deeper soil layers, respectively. Organic carbon storage in the later stages of succession ranged from 1.1 – 7.9 kg C m⁻². A larger amount of organic carbon, including ancient carbon in a raised beach deposit, was expected to be contained in much deeper soil layers. These results suggest that both vegetation development and geological history affect ecosystem carbon storage and that a non-negligible amount of organic carbon is distributed in this High Arctic glacier foreland.  相似文献   

Fractal structure of spatial distribution of microfracturing in rock   总被引：10，自引：0，他引：10  

Takayuki Hirata  Takashi Satoh  Keisuke Ito 《Geophysical Journal International》1987,90(2):369-374

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Correlated δ18O and [Ti] in lunar zircons: a terrestrial perspective for magma temperatures and water content on the Moon     

John W. Valley  Michael J. Spicuzza  Takayuki Ushikubo 《Contributions to Mineralogy and Petrology》2014,167(1):1-15

Zircon grains were separated from lunar regolith and rocks returned from four Apollo landing sites, and analyzed in situ by secondary ion mass spectrometry. Many regolith zircons preserve magmatic δ¹⁸O and trace element compositions and, although out of petrologic context, represent a relatively unexplored resource for study of the Moon and possibly other bodies in the solar system. The combination of oxygen isotope ratios and [Ti] provides a unique geochemical signature that identifies zircons from the Moon. The oxygen isotope ratios of lunar zircons are remarkably constant and unexpectedly higher in δ¹⁸O (5.61 ± 0.07 ‰ VSMOW) than zircons from Earth’s oceanic crust (5.20 ± 0.03 ‰) even though mare basalt whole-rock samples are nearly the same in δ¹⁸O as oceanic basalts on Earth (~5.6 ‰). Thus, the average fractionation of oxygen isotopes between primitive basalt and zircon is smaller on the Moon [Δ¹⁸O(WR-Zrc) = 0.08 ± 0.09 ‰] than on Earth (0.37 ± 0.04 ‰). The smaller fractionations on the Moon suggest higher temperatures of zircon crystallization in lunar magmas and are consistent with higher [Ti] in lunar zircons. Phase equilibria estimates also indicate high temperatures for lunar magmas, but not specifically for evolved zircon-forming melts. If the solidus temperature of a given magma is a function of its water content, then so is the crystallization temperature of any zircon forming in that melt. The systematic nature of O and Ti data for lunar zircons suggests a model based on the following observations. Many of the analyzed lunar zircons are likely from K, rare earth elements, P (KREEP)-Zr-rich magmas. Zircon does not saturate in normal mafic magmas; igneous zircons in mafic rocks are typically late and formed in the last most evolved portion of melts. Even if initial bulk water content is moderately low, the late zircon-forming melt can concentrate water locally. In general, water lowers crystallization temperatures, in which case late igneous zircon can form at significantly lower temperatures than the solidus inferred for a bulk-rock composition. Although lunar basalts could readily lose H₂ to space during eruption, lowering water fugacity; the morphology, large size, and presence in plutonic rocks suggest that many zircons crystallized at depths that retarded degassing. In this case, the crystallization temperatures of zircons are a sensitive monitor of the water content of the parental magma as well as the evolved zircon-forming melt. If the smaller Δ¹⁸O(zircon–mare basalt) values reported here are characteristic of the Moon, then that would suggest that even highly evolved zircon-forming magmas on the Moon crystallized at higher temperature than similar magmas on Earth and that magmas, though not necessarily water-free, were generally drier on the Moon.  相似文献   

Fluid Inclusion Studies from the Wyanad Gold Field, S. India: Evidence for Nature, Composition, Density and P-T Conditions of Ore Fluids     

S.S. Binu-Lal  Takayuki Sawaki  Hideki Wada  M. Santosh 《Gondwana Research》2001,4(4):578-579

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The layered structure of lunar maria: Identification of the HF-radar reflector in Mare Serenitatis using multiband optical images     

Shoko Oshigami  Shinya Okuno  Yasushi Yamaguchi  Makiko Ohtake  Junichi Haruyama  Takao Kobayashi  Atsushi Kumamoto  Takayuki Ono 《Icarus》2012,218(1):506-512

Comparison of the Lunar Radar Sounder (LRS) data to the Multiband Imager (MI) data is performed to identify the subsurface reflectors in Mare Serenitatis. The LRS is FM-CW radar (4–6 MHz) and the 2 MHz bandwidth leads to the range resolution of 75 m in a vacuum, whereas the sampling interval in the flight direction is about 75 m when an altitude of the spacecraft with polar orbit is nominal (100 km). Horizontally continuous reflectors were clearly detected by LRS in limited areas that consist of about 9% of the whole maria. The typical depth of the reflectors is estimated to be a few hundred meters. Layered structures of mare basalts are also discernible on some crater walls in the MI data of the visible bands (VIS). The VIS range has nine wavelengths of 415, 750, 900, 950, and 1000 nm, and their spatial resolution is 20 m/pixel at a nominal altitude. The stratigraphies around Bessel and Bessel-H craters in Mare Serenitatis are examined in this paper. It was revealed that the subsurface reflectors lie on the boundaries between basalt units with different chemical compositions. In addition, model calculations using the simplified radar equation indicate that the subsurface reflectors are not compositional interfaces but layer boundaries with a high-porosity contrast. These results suggest that the detected reflectors in Mare Serenitatis are regolith accumulated during so long hiatus of mare volcanisms enough for chemical composition of magma to change, not instantaneously. Therefore combination of the LRS and MI data has a potential to reveal characteristics of a series of magmatism forming each lithostratigraphic unit in Mare Serenitatis and other maria.  相似文献