In this paper we report crystal/groundmass partition coefficients of a large set of major and trace elements for the main phenocryst minerals occurring in the potassium-rich volcanic rocks from the Roman comagmatic province, Central-Southern Italy. Based on these data, the patterns of major and trace element variation during the low-pressure evolution of alkaline potassic magmas are briefly discussed.

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Oceanographic studies including CTD survey of warm sites and bottom photography confirmed several hydrothermal fields on the summit of Loihi Seamount, Hawaii. Warm water venting at these sites forms chimneys sticking out of and veins cutting through older precipitates. The summit is covered with hydrothermal plumes which are extremely rich in methane, helium, carbon dioxide, iron and manganese, the maximum concentration of helium being 91.8nl/l, the highest so far reported for open-ocean water. The ³He/⁴He ratio of helium injected into seawater is 14 times the atmospheric (1.4 × 10^-6) and similar to that reported for Kilauea and other hotspot-volcanic gases. The ³He/heat and CO₂/heat ratios in the plume are one to two orders of magnitude greater than those at oceanic spreading centers, implying a more primitive source region for hotspot volcanism. The Loihi plumes show negative pH anomalies up to half a pH unit from ambient owing to the high injection rate of CO₂.

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A simplified analysis of He, Ne, and Ar dissolved in natural waters is proposed. The principle of this method is the gas chromatographic determination of noble gases contained in a gas phase which is placed in dissolution equilibrium with a sample water. This method does not need any vacuum line or complicated procedure. Although this method is applicable to any gas species dissolved in water, it is useful for routine analyses of He, because high sensitivity of this simplified method enables to determine a He content as low as 50 ppb, the amount of dissolved He in water equilibrated with air.

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A method using pure zinc wire for the preparation of hydrogen gas for the D/H ratio measurement has been developed. Complete conversion of water samples into hydrogen gas is achieved in a reaction vessel made of glass (quartz and Pyrex glass). The statistical treatment suggests that hydrogen derived from zinc and the material of the reaction vessel affects the accuracy of the D/H ratio measurement.

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Comparison of oxygen isotopic ratios in whole rocks and some constituent minerals were made between a small (300m × 100m) hydrothermal alteration area and the surrounding diagenetically altered area in the Tsugaru-Yunosawa geothermal field. The δ¹⁸O values of whole rocks are distinctly higher in the area subjected to hydrothermal alteration than those in the only diagenetically altered area. The oxygen isotope fractionations among the alteration minerals are nearly identical in the two areas. This suggests an isotopic equilibrium between the minerals and waters responsible for alteration. Therefore, the difference of 7‰ in δ¹⁸O values of minerals between hydrothermally and diagenetically altered areas may correspond to the difference in isotopic composition between waters responsible for these two types of alteration. The origin of the water responsible for the hydrothermal alteration seems to be related to the fossil seawater postulated as the source of the hot springs in and around this geothermal field. The δ¹⁸O value of the hydrothermal water responsible for the alteration was estimated to be in a range from about 0 to +7‰, based on the δ¹⁸O values of cristobalites in the hydrothermally altered area, the range of the estimated alteration temperature and the δ¹⁸O values of the present-day hot spring waters. The δ¹⁸O value of the water during the diagenetic alteration is lower by 7‰ than that of the hydrothermal water, but is higher than that of meteoric water.

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