查看更多>>摘要：The Pacific coast of Japan has repeatedly suffered earthquakes with magnitudes greater than M-w 8 and accompanying tsunami on coastal areas. Estimating the inundation area of paleotsunami using event deposits in sediment layers can inform and reduce possible damages from future earthquakes and tsunami. In addition to geological and sedimentological analyses, the geochemical signature of sediments can be an effective proxy for identifying event deposits in many cases. However, few geochemical analyses have been applied to study the Pacific coast of middle Japan. Therefore, the geochemical characteristics of paleotsunami deposits (similar to 1000, 3500, and 4000 cal BP) were assessed for core samples from the Shizuoka plain (Oya lowland) on the Pacific coast of middle Japan. In a ternary diagram for (Na2O+CaO)-Al2O3-(Cr+Ni), our data from the paleotsunami deposits from the Shizuoka plain plotted between those of the beach core samples (shoreface and dune deposits) and mud layers in the back marsh deposits. Additionally, vertical and horizontal distributions of titanium normalized values (Na/Ti, Sr/Ti, Ba/Ti, and Cr/Ti atomic ratios) and Si/Al atomic ratios in the cores from the Shizuoka plain provided important clues for discrimination of the paleotsunami deposits from other layers, such as flood deposits from river overflow and mud layers that settled in calm environments. Based on the cluster analysis, the data from the paleotsunami deposits (similar to 3500 cal BP) were discriminated from those of other layers in our case.
查看更多>>摘要：The quartzofeldspathic gneiss of the Shillong Plateau Gneissic Complex has preserved magnetite-centered ocellar texture or fleck structure. Results presented in this work suggest that the intrusion of hot, volatile-rich pegmatitic magma into the thermally elevated quartzofeldspathic gneiss during the late Pan-African tectonothermal event initiated very localized partial melting in the latter forming neosomes. After their formation, the neosomes were infiltrated by the highly-viscous pegmatite magma leading to chaotic mixing between the two magmatic phases. The occurrence of chaotic mixing enabled the pegmatite magma to venture into the neosomes as veins or filaments by stretching and folding dynamics. As the pegmatitic veins traversed through the partially molten rocks or neosomes due to advection, substantial stretching caused the veins to develop sinuous perturbations. Eventually, the perturbations magnified and nascent swirls began to grow on the sinuous filaments by concentrating the high-viscosity pegmatitic veins into globules and impoverishing the areas in between them. Gradually, the globules separated from each other and commingled with the surrounding neosome, producing individual emulsions or ocelli. The viscous swirling phenomenon produced discrete diffusive elements that significantly enhanced the interfacial area between the two magmatic phases, which promoted diffusion and eased mixing between them.
查看更多>>摘要：ERM-CZ120 is a certified reference material (CRM) for fine particulate matter (PM). Still, only a small number of values are available in the literature for its metallic element concentrations and lead isotope ratios. In this study, the elemental composition and lead isotope ratios of 5-10 mg of ERM-CZ120 were analyzed nine times to determine its geochemical characteristics. Inductively coupled plasma mass spectrometry (ICP-MS) was applied to samples after microwave digestion by nitric acid, hydrogen peroxide, and hydrofluoric acid. The average observed values of ERM- CZ120 were 90-110% of the certified values or additional material information values for 29 elements. However, there were clear differences between the observed and certified or additional material information values for Zr, Hf, and Au. The relative uncertainties were measured to be < 10% for 45 elements. However, the relative uncertainties in the observed values for B, Pt, and Au were similar to 50%. The representativeness for the average observed values of B, Zr, Hf, Pt, and Au seemed to be low. The crude samples and grain-size refined samples of NIES CRM No. 8 were analyzed using the same method as that for ERM-CZ120. Observations suggested that grain-size refining did not always reduce bias and dispersion for the nine times analysis of similar to 5-10 mg samples of NIES CRM No. 8. NIES CRM No. 8 has much higher carbon content than ERM-CZ120 and actual PM2.5 samples. The observations may be because of the interference in digestion by incompletely digested carbon in [HNO3 + H2O2 + HF] microwave digestion. Both ERM-CZ120 and NIES CRM No. 8 indicated enriched levels of various metals compared to crustal material, indicating anthropogenic activity contributions. Moreover, B, Se, W, and Pb levels were an order of magnitude higher for NIES CRM No. 8 than for ERM-CZ120. ERM-CZ120 had lower Pb-207/Pb-206 and Pb-208/Pb-206 than NIES CRM No. 8. The lead isotope ratios of ERM-CZ120 coincide with the ratios of
查看更多>>摘要：Recent studies have reported slight but definite differences in.'17O between the lithosphere and hydrosphere. In the present study, we precisely and accurately quantify the.'17O values of geothermal H2O and mid-ocean ridge basalt (MORB) with normalization on the VSMOW- SLAP scale to further substantiate these differences and to discuss the isotopic evolution of the hydrosphere throughout the geologic time scale. With a.'17O value of -60 +/- 13 x 10-6, the.' 17O value of MORB is comparable with that in other silicates reported in previous studies. However, the.'17O value of geothermal H2O tended to decrease from +31 x 10- 6 to -51 x 10-6, which are the usual.'17O values in meteoric water and silicates, respectively, in accordance with the 18O- enrichment. These results imply an active oxygen isotope exchange between silicates and geothermal H2O under high-temperature conditions at depth. This is supported by previous studies which report the 17O- enrichment of silicate altered by hydrothermal H2O. Considering this direct evidence for depletion of 17O, we conclude that the 17O-depleted H2O has been supplied continuously to the hydrosphere. Additionally, low-temperature interaction between the silicates and H2O besides high-temperature hydrothermal interaction must be assumed to explain the observed.'17O of the terrestrial hydrosphere. We conclude that the.' 17O of the terrestrial hydrosphere should have been variable throughout the geologic time scale owing to the various oxygen exchange interaction between the lithosphere and hydrosphere.
NSTL
Geochemical Soc Japan