Rb-Sr ages of biotite from the southern flank of Mt. Everest, eastern Nepal, range from 14.1 to 1.3m.y., the youngest b-iotite coexists with muscovite of 7.3m.y.These different ages for different samples reflect the difference in cooling history related to the uplift of the Himalayas.The biotite ages decrease with increasing distance from the high mountain range, suggesting that the high range, i.e., the northern area, was uplifted earlier than the southern area. The relationship between the ages and altitudes of sampling sites indicates that the uplift rate of the northern area was 0.60 mm/yr.
The chemical and physical features of the deeper part of the Fushime geothermal system (about 1000-2000 m depth), where temperatures exceed 300°C, have been revealed in the course of its explora tion. The fluids discharged from wells are saline, and the maximum Cl concentrations of the reservoir waters are similar to that of seawater. The waters are depleted in Mg and SO4 but are enriched in K, Ca, Fe, Mn, Zn, Pb, Si02, etc., over those of seawater, suggesting that the geothermal fluid originates from high temperature seawater-rock interaction. Relatively long term discharge testing shows that excess en thalpy conditions (i.e. two-phase feed) commonly develop, and that isothermal boiling has also occurred in the high temperature reservoir. The fluid chemical compositions that are the least disturbed by these physical processes caused by testing were selected from the data base for study. They indicate that boil ing and dilution predominate in the undisturbed reservoir. Variations in the K and Ca concentrations of the waters suggest that the precipitation of K-bearing minerals and the dissolution of Ca-bearing minerals occur in the reservoir.Fluid-mineral equilibria for the Fushime reservoir waters were calculated without allowing for redox reactions for dissolved gases (CH4-CO2, H2-H2O and N2-NH3), because allowing for these reac tions results in an extreme discrepancy between analytical CH4, H2 and SO4 concentrations and those calculated. Calculations show that the fluids are close to anhydrite saturation and are close to equilibrium with both Na/K-feldspars. However, apparent undersaturation with respect to calcite is in dicated. Higher pH values are calculated for the reservoir waters in relatively lower temperature wells (the measured pH values are also higher than those of the higher temperature wells). They are approx imately in equilibrium with K-feldspar and K-mica at reservoir conditions. In contrast, the lower pH waters in wells with higher temperature are not calculated to be in equilibrium with this pair. The latter is inconsistent with the observation that these two minerals are common as alteration products. The numerical back titration into the fluids of sphalerite and galena, which are observed in scale deposited in the wells and surface equipment, results in a pH increase in the high temperature reservoir water. This reconciles the disagreement between the observed presence of these minerals and fluid composition of high-temperature wells. Thus, the precipitation of sphalerite and galena is the most likely source of the acidity.
Research and development on geological disposal of high-level radioactive waste have been carried out by Japan Atomic Energy Agency JAEA, previous JNC in Horonobe, the northern Hokkaido. The geology of Horonobe comprises the Neogene siliceous marine sediments which contain saline water. The origin of saline water is one of the most fundamental factors for evaluating geological environments. The synthesis of geo-scientific understanding contributes to develop a performance assessment methodology by providing a basis for setting parameters and constructing conceptual model. Geological environments are also important for exploration of oil fields. This study analysed the various data of JAEA reseach for hydro-geochemistry of Horonobe.The squeezed water and the lifted water from eight boreholes drilled in Horonobe are analyzed on oxygen and hydrogen isotopes and Cl concentration by JAEA. Based on the analytical data, the groundwater is subdivided into three groups derived from the mixtures of meteoric water and different saline waters, which distributions are consistent with the regional geologic situations. 18O, D and Cl of pore water during diagenesis of the siliceous sediments are calculated based on the assumption that water/rock interaction makes redistribution of the isotopes in rocks and pore water during the phase transformations from opal A through opal CT to quartz in open systems, then that water in biogenic silica is expelled to pore-space during the successive compaction in closed systems. The measured data points fall approximately on the mixing lines between the meteoric water and the pore waters calculated on the assumption of the phase transformations. The geological study on the diagenesis of the field shows that the silica phase transformations actually occur near the depth calculated from the porosity reduction, indicating that the transformation and the succeeding compaction contribute to the origin of the saline water.
Granitic and gneissic rocks of the Kangchenjunga range,Eastern Nepal,were analysed for Rb-Sr age and initial87Sr/86Sr ratio.Biotite and muscovite ages are ranging from•£•¥11
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