GEOCHEMICAL JOURNAL

Isotopic evidence of paleowaters in the Po sedimentary basin (Northern Italy)

Carlo Gorgni, Giovanni Martinelli, Gian Paolo Sighinolfi

1982 Volume 16 Issue 2 Pages 51-61
Published: April 20, 1982
Released on J-STAGE: April 08, 2008

DOIhttps://doi.org/10.2343/geochemj.16.51

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Stable isotopic composition and radiometric age were measured for groundwaters in the Emilia area of the Po sedimentary basin (Northern Italy). Waters from unconfined shallower aquifers, deep circulating continental waters and sodium chloride waters (relic waters) squeezed out from underlying marine formations during past geological events were considered. Waters from supposed confined aquifers (paleowaters) are usually depleted in 0–18 (δ¹⁸O < -10‰) and their δ¹⁸O–δD relationships are not consistent with their belonging to the present hydrological cycle. Isotope data on sodium chloride waters suggest mixing of relic saline waters with deep circulating continental waters. Processes affecting stable isotope composition of groundwaters in unconsolidated sediments are discussed. Oxygen isotope chemistry is considered to be a rather conservative parameter at least at low temperatures, thus able to give paleoclimatic information. Some ¹⁴C age data on deep circulating groundwaters suggest permanence times within the aquifers greater than 15, 000yrs in some cases. These data agree with paleoclimatological deductions in pointing out the presence of paleowaters in the Po sedimentary basin.

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Variations in chemical and isotopic compositions of fumarolic gases from Showashinzan volcano, Hokkaido, Japan

Yoshihiko Mizutani, Tsutomu Sugiura

1982 Volume 16 Issue 2 Pages 63-71
Published: April 20, 1982
Released on J-STAGE: April 08, 2008

DOIhttps://doi.org/10.2343/geochemj.16.63

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Fumarolic gas samples collected from the hottest fumarole of the Showashinzan volcano on 15 occasions during the period from 1954 to 1978 have been examined for chemical and isotopic compositions. The fumarolic gases considerably changed their composition and temperature with time, owing probably to exhaustion of primary volcanic gases and mixing with water vapor originated from local surface waters soaking into the volcano. It has been also shown that the atmospheric contamination, lowering of temperature and reactions with the surrounding materials were important additional factors involved in the alteration of fumarolic gases. The change in gas composition with time may be considered to be indicative of the history of a volcanic hydrothermal system formed by intrusion of dacite magma.

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D/H fractionation between water and the melts of quartz, K-feldspar, albite and anorthite at high temperature and pressure

Yoshimasu Kuroda, Yu Hariya, Tetsuro Suzuoki, Sadao Matsuo

1982 Volume 16 Issue 2 Pages 73-78
Published: April 20, 1982
Released on J-STAGE: April 08, 2008

DOIhttps://doi.org/10.2343/geochemj.16.73

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Quartz, K-feldspar, albite and anorthite were equilibrated with water vapor in Pt capsules at 20kb and in the temperature range from 800 to 1, 300°C. The water in the capsules during the high temperature and pressure run seems to exist in two states, aqueous fluid and dissolved water (structural water) in the melt. In the process of extracting these waters, four kinds of water were distinguished experimentally: 1) Water extracted by puncturing the capsule in vacuum, 2) Water released from bubbles in quenched products, i.e., glasses, during grinding in an agate mortar, 3) Water extracted from pulverized product in evacuation process at room temperature, and 4) Water extracted in vacuum at high temperature. D/H ratios of waters of 1), 3) and 4) were measured. Taking water 4) to be dissolved water in melt, the fractionation factors between this and other waters from aqueous fluid were estimated. Deuterium is enriched in the dissolved water for albite and K-feldspar melts, D/H is almost the same for the aqueous fluid and dissolved water in the anorthite melt, and deuterium is much depleted in the dissolved water in the quartz melt.

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Sr/Ca-Ba/Ca systematics in Miyakejima, Onoharajima, Mikurajima and Inambajima volcanoes, the Izu Islands, Japan

Masataka Hirano, Naoki Isshiki, Naoki Onuma

1982 Volume 16 Issue 2 Pages 79-87
Published: April 20, 1982
Released on J-STAGE: April 08, 2008

DOIhttps://doi.org/10.2343/geochemj.16.79

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Ca, Sr and Ba contents of basalts and andesites from Miyakejima, Onoharajima, Mikurajima and Inambajima volcanoes, the Izu Islands, Japan, have been determined by an inductively coupled plasma optical emission spectrometer. The data reveal that Miyakejima, Onoharajima and Mikurajima volcanoes gave three different series of Sr/Ca-Ba/Ca systematics, while an Inambajima andesite belongs to Mikurajima systematics. The difference is considered to reflect different degrees of partial melting of a common mantle material with chondritic Sr/Ca and Ba/Ca ratios. The degree of partial melting decreases from Oshima to Miyakejima and is constant from Miyakejima to Mikurajima along the arc, while it decreases from Miyakejima to Onoharajima across the arc. Therefore, there seems to be no relationship between the “degree” of partial melting and the distance from the Izu-Ogasawara Trench in this region.

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Stable isotopes and fluid inclusion study of anhydrite from the East Pacific Rise at 21°N

Minoru Kusakabe, Hitoshi Chiba, Hiroshi Ohmoto

1982 Volume 16 Issue 2 Pages 89-95
Published: April 20, 1982
Released on J-STAGE: April 08, 2008

DOIhttps://doi.org/10.2343/geochemj.16.89

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Six anhydrite samples from the submarine hydrothermal sulphide/sulphate mineral deposits found along the crest of the East Pacific Rise at 21 °N have been examined for filling temperature of fluid inclusions and for ³⁴S/³²S and ¹⁸O/¹⁶O ratios. The anhydrite was precipitated upon mixing of hot (260–350°C), SO₄^2--poor hydrothermal fluids with cold seawater at various proportions, which is reflected in a large variation in the filling temperatures ranging from 180°C to almost the highest exit temperatures. Seawater sulphate origin for anhydrite-sulphur is indicated by the δ³⁴S values that are essentially identical with the present-day seawater sulphate value, whereas the δ¹⁸O values are up to 2‰ higher than the seawater sulphate value. The anhydrites are not in oxygen isotopic equilibrium with the mixed solution at measured exit temperatures of 260 to 350°C. However, this enrichment of ¹⁸O may be attributed to partial equilibration of fine-grained anhydrite with solutions at lower temperatures after deposition. Absence of anhydrite at dead vents suggests that SO₄^2- slightly enriched in ¹⁸O is added to seawater sulphate owing to dissolution of anhydrite after the cessation of a high temperature stage of the hydrothermal activity.

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¹H-NMR T₁ as a possible parameter to diagenesis

Shin-ichi Hirata, Masahiko Akiyama

1982 Volume 16 Issue 2 Pages 97-98
Published: April 20, 1982
Released on J-STAGE: April 08, 2008

DOIhttps://doi.org/10.2343/geochemj.16.97

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