Annual fluctuation in the stable carbon isotope ratio of coral skeletons: The relative intensities of kinetic and metabolic isotope effects     

Tamano Omata  Atsushi Suzuki  Mineo Okamoto 《Geochimica et cosmochimica acta》2005,69(12):3007-3016

Stable carbon and oxygen isotope measurements of biogenic carbonate provide information for reconstructing past oceanic environments. In particular, ¹⁸O/¹⁶O ratios correlate with the temperature and salinity of seawater and ¹³C/¹²C is a proxy for dissolved inorganic carbon in seawater and symbiont photosynthesis. Here, we report ¹³C/¹²C and ¹⁸O/¹⁶O values for skeletons of corals (genus Porites) with various growth rates. In faster-growing corals, ¹³C/¹²C and ¹⁸O/¹⁶O showed out-of-phase annual fluctuations. In slower-growing corals, the isotopes fluctuated in phase. We developed a simple vector notation to show two patterns of ¹³C/¹²C annual fluctuation, each with a different offset in relation to ¹⁸O/¹⁶O annual fluctuation. The phase offset between ¹³C/¹²C and ¹⁸O/¹⁶O annual fluctuations depends on the relative intensities of kinetic isotope effects on calcification and metabolic isotope effects such as photosynthesis. This model might improve our ability to infer past climate and oceanographic conditions from coral skeletons.  相似文献   

Application of differential thermodynamics (Gibbs' method) to amphibole zonings in the metabasic system     

Atsushi Okamoto  Mitsuhiro Toriumi 《Contributions to Mineralogy and Petrology》2001,141(3):268-286

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Mineral distribution within polymineralic veins in the Sanbagawa belt,Japan: implications for mass transfer during vein formation     

Atsushi Okamoto  Taketo Kikuchi  Noriyoshi Tsuchiya 《Contributions to Mineralogy and Petrology》2008,156(3):323-336

Pelitic schists of the Sanbagawa metamorphic belt contain several types of polymineralic veins that formed during the late stages of exhumation. The vein mineral assemblages are quartz + albite + K-feldspar + chlorite ± calcite (Type I, II) and quartz + albite + calcite (Type III). Type I and II veins contain quartz and albite with stretched-crystal and elongate-blocky textures, respectively. The mineral species within Type I veins vary with compositional bands within the host rocks. Type III veins are characterized by euhedral to subhedral quartz grains with concentric zoning and a homogeneous distribution along the vein length. The vein textures vary depending on the crack aperture during multiple crack-seal events: <0.08 mm for Type I, and 0.5–10 mm for Type III. Type II veins show intermediate features between Type I and III veins in terms of mineral distribution (weak dependence on the host rock composition) and apparent crack aperture (less than 1–15 mm). These observations suggest a transition in the dominant transport mechanism of vein components with increasing crack aperture, from diffusion from host rocks to fluid advection along cracks.  相似文献   

The roles of fluid transport and surface reaction in reaction-induced fracturing,with implications for the development of mesh textures in serpentinites     

Hiroyuki Shimizu  Atsushi Okamoto 《Contributions to Mineralogy and Petrology》2016,171(8-9):73

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Characterization of serpentinization in olivine-orthopyroxene-H2O system revealed by thermogravimetric and multivariate statistical analyses     

Atsushi Okamoto  Shuhei Tanaka  Masaoki Uno  Otgonbayar Dandar  Kazuki Yoshida 《Island Arc》2024,33(1):e12519

Thermogravimetric (TG) analyses were used to characterize the products and quantify the extent of serpentinization as a stepwise weight loss during heating (TG loss) or its derivative (DTG). Multivariate analyses are powerful tools for extracting information from complicated spectrum data; however, no studies have applied them to characterize serpentinites. In this study, hydrothermal experiments of olivine-H₂O, olivine–orthopyroxene-H₂O and orthopyroxene-H₂O were conducted at 250–400°C and under vapor-saturated pressure. The product minerals observed were serpentine+brucite+magnetite in the olivine-H₂O experiments and serpentine±talc in the orthoyroxene-H₂O and olivine-orthopyroxene-H₂O experiments. These results are consistent with those of previous studies; however, the positions and width of DTG peaks for individual minerals were varied depending on the experimental conditions. To extract systematics from the TG spectra, non-negative matrix factorization (NMF), an unsupervised machine learning technique, was applied to the DTG spectra of the experimental products. NMF revealed that the DTG profiles were explained by a linear combination of six basis spectra, which corresponded to the characteristic products, including three types of serpentine minerals (low-, medium-, and high-T), two types of brucite (low-and high-T), two type of talc (talc+serpentine mixture, well-crystallized talc) with different crystallinity, and noise during the TG measurement. Systematic changes in the factor loading revealed that, in the olivine-H₂O systems, the products changed from medium-T serpentine+low-T brucite to high-T serpentine+high-T brucite as serpentinization progressed. In the olivine-orthopyroxene system, low-T serpentine or poorly crystallized talc+serpentine mixture was initially formed, followed by the formation of well-crystallized talc, resulting in dehydration. Applying NMF to DTG showed the mineralogical differences between olivine and orthopyroxene systems and increases of the crystallinity during the progress of serpentinization, suggesting its potential for characterizing various serpentinites within oceanic lithospheres that suffer from several stages of alteration and weathering at different temperatures.  相似文献   

Fluctuations in isothermal spheres     

Joseph Katz  Isao Okamoto 《Monthly notices of the Royal Astronomical Society》2000,317(1):163-169

Isolated isothermal spheres of N gravitationally interacting points with equal mass are believed to be stable when density contrasts do not exceed 709. That stability limit does not, however, take into consideration fluctuations of temperature near the onset of instability. These are important when N is finite.
Here we correlate global mean quadratic temperature fluctuations with the onset of instability. We show that such fluctuations trigger instability when the density contrast reaches a value near 709×exp(−3.3 N ^−1/3). These lower values of limiting density contrasts are significantly smaller than 709 when N is not very large, and this suggests (i) that numerical calculations with small N may not reflect correctly the onset of core collapse in clusters with large N , and (ii) that a greater number of globular clusters than is normally believed may already be in an advanced stage of core collapse, because most of the observed globular clusters with parameters that fit quasi-isothermal configurations are close to marginal stability.  相似文献   

Acceleration and collimation of magnetized winds     

Isao Okamoto 《Monthly notices of the Royal Astronomical Society》2000,318(1):250-262

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Reply to Comment on ‘Metamorphic olivine after dehydration embrittlement in Serpentinite: Case study from the Shiraga Serpentinite mass in the Sanbagawa high P/T metamorphic belt,central Shikoku,Japan’ by Wallis and Endo,https://doi.org/10.1111/iar.12328     

Seiya Fukumura  Kazuaki Okamoto  Masaru Terabayashi 《Island Arc》2020,29(1)

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Geochemical Characteristics of Apatite in Heavy REE‐rich Deep‐Sea Mud from Minami‐Torishima Area,Southeastern Japan     

Yoshiaki Kon  Mihoko Hoshino  Kenzo Sanematsu  Sayaka Morita  Maiko Tsunematsu  Nobuyuki Okamoto  Nobuhiko Yano  Mikiya Tanaka  Tetsuichi Takagi 《Resource Geology》2014,64(1):47-57

We have conducted geochemical and mineralogical investigations of the rare earth and yttrium (REY)‐rich mud from the Minami‐Torishima area in the Pacific in order to clarify the concentration of REY and their host‐phase in the mud. X‐ray diffraction analysis shows that the mud is mainly composed of phillipsite, fluorapatite, quartz, albite, illite and montmorillonite. Whole‐rock CaO, P₂O₅ and total REY contents of the mud are positively correlated. Relative abundance of apatite is also positively correlated to P₂O₅ and total REY contents. These correlations suggest that apatite is the main host of the P₂O₅ and REY in the mud. We make in situ compositional analyses of constituent minerals in the REY mud. The results show that the apatite is abundant in REY (9300–32,000 ppm) and is characterized by a negative Ce anomaly and enrichment in heavy rare‐earth elements. This abundance and composition of REY of the mud is similar those of fish debris apatites. In contrast, phillipsite is less abundant in REY (60–170 ppm). Therefore we conclude that the main REY host phase of the mud is apatite.  相似文献   

Doppler shifts of metallic lines for a white-light flare     

M. D. Ding  C. Fang  T. Okamoto 《Solar physics》1994,149(1):143-148

In this paper we investigate the Doppler shifts of the metallic lines for a 3B white-light flare on September 19, 1979. The results show that there is no systematic shift at the line center, while there may appear some asymmetry at the line wing. A possible heating process of this flare is proposed to interpret the observed spectral features.  相似文献