Sadao Matsuo

Partition of chlorine compounds between silicate melt and hydrothermal solutions: I. Partition of NaCl-KCl

Abstract The partition experiments of NaCl and KCl between silicate melts and aqueous chloride solutions were carried at a temperature of 810°C in the pressure range from 0.6 to 6.0 kb. The chloride concentration in the melt (CClm) was constant in certain ranges of chloride concentration in the aqueous phase (CClaq) at 0.6 and 1.2 kb, which reveals the presence of vapor-liquid immiscibility of the aqueous solution. The variation diagram of CClm and CClaq can be applied to the study of aqueous phases as a new method. The partition ratio of chloride ( D Cl m aq = C Cl m C Cl aq ) exhibits a strong negative pressure dependence, which is attributed to the large negative partial molar volume of chlorides in the aqueous phase. The distribution coefficient of Na and K ( D Na K M Aq = ( C Na m C K m / C Na aq C K aq )) is about 0.75 and has little pressure dependence at pressures higher than 2.2 kb. The distribution coefficient, however, has a positive pressure dependence at pressures lower than 1.2 kb.

Oxygen isotope fractionation factors between anhydrite and water from 100 to 550°C

Oxygen isotope exchange between anhydrite and water was studied from 100 to 550°C, using the partial equilibrium method. The exchange rate was extremely low in NaCl solution. In the lower-temperature range, acid solutions were used to produce sufficient reaction to determine the oxygen isotope fractionation factors. The fractionation factors obtained in the present study are definitely different from those given by Lloyd [8]. They are similar to those for the HSO4−-water system studied by Mizutani and Rafter [19], and are consistently 2‰ higher than those of the barite-water system by Kusakabe and Robinson [5]. The temperature dependence of the oxygen isotope fractionation factors was calculated by the least squares method in which the weight was taken to be inversely proportional to the experimental error. The fractionation is given by:103lnαanhydrite-water=3.21×(103/T)2−4.72 Available δ18O values of natural anhydrite were used to test the validity of this expression. It is shown that this newly revised geothermometer can be successfully applied to natural hydrothermal anhydrite.

Hydrogen isotope composition of deep-seated water

D/H ratios of phlogopites and amphiboles from rocks of possible mantle origin and also those of water from (glass?) inclusions in olivines of the olivine nodule and peridotites have been determined. The mantle water seems to have aδD value of —85±10‰ on the basis of results of inclusions in the nodule-olivine.

Hydrogen isotopic fractionation factor between brucite and water in the temperature range from 100° to 510° C

The hydrogen isotopic fractionation factor between brucite and water has been determined in the temperature range of 100°–510° C. Brucite is always depleted in deuterium relative to the coexisting water, and the degree of depletion becomes larger with decreasing temperature. The fractionation factor changes smoothly in the temperature range of 144°–510° C and its temperature dependence was obtained by the method of least square fit in the following form: 103Inα=8.72×106T−2−3.86×104T−1+14.5However, a marked decrease of about 5‰ was observed at 100°–144° C. The D/H fractionation factor for the brucite-water system is not similar to that for serpentine-water system presented by Sakai and Tsutsumi (1978), though all the hydroxyl ions coordinate to magnesium ion in both minerals. This discrepancy cannot be attributed to hydrogen bonding but to distortion of Mg-octahedron of serpentine, in which the Mg-OH bonding length is shorter than the sum of ionic radius of Mg2+ and O2− and there is no distortion in brucite. It is indicated that aside from hydrogen bonding, the structure effect also controls the D/H fractionation between hydrous mineral and water.

D/H ratios of the coexisting phlogopite and richterite from mica nodules and a peridotite in South African kimberlites

The water content and D/H ratio of pairs of phlogopite and richterite in kimberlite samples were measured. The water contents of both minerals were lower than the formula content. On the basis of D/H ratios of the pair, phlogopite and richterite can not be regarded as a simple equilibrium product with respect to hydrogen isotope exchange. It seems impossible to estimate D/H ratio of the mantle water through D/H ratios of the hydrous silicate pairs.

Vapor Pressure of Ice Containing D2O

The vapor pressures of solid D2O and ice containing D2O in various amounts were measured with an oil manometer. The result gives the lowest vapor pressure for D2O ice ever obtained. The observed value for ice with different proportions of D2O and H2O agreed well with the values calculated on the assumption that the vapor pressure of HDO is the geometrical mean of those of H2O and D2O and that the equilibrium constant of isotopic exchange is 4. The fractionation factor of D between ice and vapor phases increases from 1.128 at 0�C to 1.210 at —38�C.

A preliminary study of D/H ratios of chlorites

Chemistry dependence of δD of chlorites is inferred from data for natural chlorites. δD of water equilibrated with those chlorites is estimated to be −2∼−8‰.

D/H study of the magnetite-series granitic plutons from the Kitakami district, Northeast Japan

Abstract δD- and X Fe -values of coexisting biotite and hornblende in the magnetite-series granitic plutons from the Kitakami district were investigated. The slopes of tie-lines of coexisting biotite and hornblende in the δD- X Fe diagram are parallel to those obtained from Suzuoki and Epsteins experimental work of D/H fractionation among biotite- and hornblende-water systems. The δD- and X Fe -values of biotite and hornblende become lower during crystallization, i.e. δD-values vary from −65 to −85% for biotite and −60 to −80% for hornblende, and X Fe from 0.5 to 0.4 for biotite and 0.4 to 0.3 for hornblende. These δD- X Fe relationships are different from those of the ilmenite-series granitic rocks, and are explained by an open-system shallow magma reservoir of comparatively high oxygen fugacity. The estimated δD-values of the magmatic waters are in the range from −60 to −40%.

Deuterium/Hydrogen Ratios and Water Content of Some Silicate Melts at High Pressure

Various approaches have been made by different workers to determine the role of water in the mantle or the lower crust. For example, Kuroda et al. [1] determined the water content of some hydrosilicate minerals under high pressure and high temperature conditions. The stability field of some hydro-silicate minerals was studied by Kushiro [2], Kushiro et al. [3], Lambert and Wyllie [4], Hariya et al. [5,6] and others. The investigations of the role of water on the magma genesis (Allen et al. [7], Kushiro [8], and Burnham and Davis [9]) and the hydrogen and oxygen isotope frac-tionation of hydrous minerals (Kokubo et al. [10], Sheppard and Epstein [11], and Kuroda et al. [12]) also provide valuable information as to the concentration of water in the upper mantle or the lower crust.