GEOCHEMICAL JOURNAL Vol. 51(2017) No. 3

Microinclusions in cuboid diamonds represent the mantle-derived fluid or melt from which they crystallized. The low degree of N aggregation in diamonds with microinclusions (cuboid or coated diamonds) indicates a short mantle residence and suggests that they crystallized shortly before kimberlite eruption. New data on the composition of microinclusions in cuboid diamonds from V. Grib kimberlite pipe (Arkhangelsk province, NW Russia) reveal two contrasting types: carbonatitic and hydrous-silicic. Significant variations in phase relations and in the ratios between different phases in the microinclusions of different diamonds are consistent with the potentially wider compositional variations expected for local volumes of diamond-forming fluids/melts. Compared to the host kimberlites, diamond microinclusions show a strong enrichment in K, a shallower REE profile, and pronounced depletion in Ti, Zr and Y. All microinclusions in diamonds from the V. Grib kimberlite pipe show enrichment in many incompatible elements, which supports their formation by partial melting of metasomatized mantle peridotites and eclogites. These data suggest that the diamonds have crystallized from carbonate-silicate fluids/melts that were derived from a source also common to kimberlites.

Lead species in size-fractionated aerosol particles collected at Higashi-Hiroshima, Japan, were determined by bulk and micro-X-ray absorption fine structure (μ-XAFS) spectroscopy and microbeam X-ray fluorescence (μ-XRF) analysis with thermodynamics calculation. The dominant Pb species in fine aerosol particles were PbSO₄, PbC₂O₄ and Pb(NO₃)₂. The species mixed internally. The Pb species in fine aerosol particles estimated by thermodynamics calculations were consistent with those estimated by XAFS spectroscopy. Results suggest that Pb species in fine aerosol particles were formed by an in-cloud process related to aquatic chemistry. In addition to the in-cloud process, heterogeneous reaction of Pb with NOx, SO₂ and oxalic acid is also an important reaction pathway for dominant Pb species in fine aerosol particles. Lead species in coarse aerosol particles were 2PbCO₃·Pb(OH)₂, Pb(NO₃)₂ and PbC₂O₄. Basic Pb carbonate, a main component of white road paint, the most dominant Pb species. The chemical reaction between 2PbCO₃·Pb(OH)₂ and HNO₃ in the atmosphere forms Pb(NO₃)₂. In addition to these dominant species, μ-XAFS detected minor species overlooked by bulk-XAFS. Thus, the combination of μ-XRF, μ-XAFS, bulk-XAFS and thermodynamics calculation is a powerful strategy for reliable and accurate Pb speciation and source apportionment.

This paper describes an analytical technique for highly precise and accurate determination of radiogenic and stable Sr isotopic composition using double-spike thermal ionization mass spectrometry. Repeated analyses of the in-house isotopic reference Wako-9999 against NIST SRM-987 gave an average δ⁸⁸Sr of +0.32‰, with a long-term 2 SD external reproducibility of ±0.02‰ (n = 15). Detailed evaluation of the Sr isotope fractionation behavior during a column chromatographic Sr separation process using Sr spec resin showed systematic variation of δ⁸⁸Sr in the eluate, from +1.05‰ to –0.64‰, as the Sr elution progressed. The Sr isotope fractionation factor between the Sr spec resin and 0.05M HNO₃ was estimated as 0.999947 ± 0.000001. During the chemical separation procedure, a very small amount of Sr with a highly fractionated isotopic composition was found to be lost in the sample loading and purification stage prior to Sr collection. This may cause a small but significant systematic mass bias in high-precision non-double-spike analyses. The analysis of 11 seawater samples from the Pacific and Atlantic oceans, including four deep seawater samples taken below the carbonate compensation depth (CCD) in the North Pacific Ocean, gave consistent results, with an average δ⁸⁸Sr of 0.407 ± 0.012‰ (2 SD). All analyzed data agreed with literature values, demonstrating the accuracy of the stable Sr analysis in this study. The δ⁸⁸Sr values of deep seawater, which were consistent with those of surface water, showed that seawater stable Sr isotopic composition is homogeneous to depths below the CCD.

We determined the stable carbon and nitrogen isotope compositions of foot tissue, conchiolin opercula, and the shell organic matrix from the marine gastropods Cernina fluctuata (Ampullinidae) and Polinices mammilla (Naticidae) collected in March 2006 from a lower tidal flat on Cuyo Island, the Philippines, together with the seagrass Enhalus acoroides and the macroalga Padina australis. The data from the foot tissue samples confirmed that the food sources for C. fluctuata were autotrophs, such as macrobenthic marine plants and algae, whereas P. mammilla may derive carbon from epiphytes and phytoplankton via their bivalve prey. The δ¹³C and δ¹⁵N values for C. fluctuata foot tissues from specimens collected in 1995 were similar to those from specimens collected in 2006. The δ¹³C values for C. fluctuata shell organics collected in 2006 were approximately 3.6‰ higher than those for P. mammilla shells, which was a similar trend to the relationship for δ¹³C values observed in their foot tissues. However, the mean δ¹³C values for the shell organics from the specimens collected in 1995 showed no significant differences between C. fluctuata and P. mammilla. In all the gastropod specimens analyzed, we observed a large (at least 10‰) δ¹³C depletion in shell organics with respect to the foot tissues of C. fluctuata and P. mammilla, although the reason for this is unclear. The δ¹³C values for the P. mammilla conchiolin opercula were similar to those for the foot tissues, whereas there was a larger δ¹³C depletion in conchiolin opercula with respect to the foot tissues of C. fluctuata. Therefore, gastropod conchiolin opercula should not be used for short-term dietary analyses in some gastropod species, but they may rather reflect the integrated long-term dietary trend.

We carried out equilibrium experiments of the CO₂-H₂O-rhyolite system at 0.1–1.5 GPa and 850 and 1200°C to examine the solubility and speciation of CO₂ in high-SiO₂ rhyolite (SiO₂ > 76 wt%). We observed that both CO₂ molecules (CO_2mol) and carbonate anions (CO₃^2–) are dissolved in the quenched rhyolitic glasses based on infrared spectroscopy. This result contrasts with the general understanding that high-SiO₂ rhyolitic melt dissolves CO_2mol only. The concentrations of CO_2mol and CO₃^2– were 199–9200 ppm and 58–2100 ppm, respectively, as quantified based on the Beer-Lambert’s law and newly determined extinction coefficients of 1192 ± 130 L·cm^–1·mol^–1 and 91 ± 28 L·cm^–1·mol^–1 for CO_2mol and CO₃^2–, respectively. The water content ranged from 2.6 to 6.1 wt%. Using the thermodynamic analysis, we calculated the partial molar volume of CO_2mol to be = 24.9 ± 2.0 cm³/mol and enthalpy of dissolution to be Δ_slnH = –22.2 ± 6.3 kJ/mol. Changes in volume and enthalpy upon the formation reaction of CO₃^2– were calculated to be Δ_rV = –8.6 ± 0.9 cm³/mol and Δ_rH = +1.1 ± 4.4 kJ/mol, respectively.

We investigated the influence of long-term sea-level changes on the groundwater flow system of a mid-latitude coastal granite area. Saline/brackish groundwaters were sampled from deep boreholes in the Hiroshima area, southwestern Japan. The origin of these waters is seawater (but not modern), as indicated by Br^–/Cl^– ratio, δD-δ¹⁸O and ³H concentration. The ³⁶Cl/Cl ratios of the seawater component of sampled water are similar to the present seawater value. The calculated ³⁶Cl ages are not more than 40 ka, indicating that the saline/brackish waters are derived from an incursion of seawater after the Last Glacial Maximum (LGM). Such a “young” seawater component is distributed within the estimated seawater inundated area during the Holocene Jomon transgression (ca. 6 ka). From the distribution of the saline/brackish waters along profiles from the present and the estimated 6 ka coast, we conclude that seawater infiltrated and reached to ~1,700 m during or after the Jomon transgression. This in turn suggests that any older saline waters were flushed out during the last glacial period, which could have been facilitated by the development of a large regional groundwater flow system. The following factors are considered to be important for the seawater incursion in crystalline rock areas: (1) permeability of the pathway (fractures), (2) the density contrast between seawater and the groundwater (freshwater) at the time of transgression, and (3) meteoric flushing during the glacial period.

The contribution of subducted sediments to the compositions of arc magmas is now widely accepted, but ratios of the sediment recycling have not been examined in detail. Here we compare the Be isotopes and B-Ba-K-Be systematics of descending sediments and erupted lavas from a cold subduction zone, the Northeast (NE) Japan Arc, to examine the sediment recycling. The descending sediments were recovered from Japan Trench, and erupted lavas were collected from three active volcanoes on the volcanic front of the NE Japan Arc. Since the subducting slab is cold, the pressure-temperature (P-T) path of its upper surface does not cross the sediment solidus, which means that the sediments would not be melted and release hydrous fluids to the overlying mantle wedge. In addition to the sediment-derived fluid, contributions of fluids from subducted altered oceanic crust (AOC) is proposed to satisfy the Be isotopes and B-Ba-K-Be systematics. Comparisons of NE Japan to other cold subduction zones show that ¹⁰Be input from Japan Trench (¹⁰Be = 488 × 10⁶ atms/g; ¹⁰Be/⁹Be = 471 × 10^–11) is middle range, but ¹⁰Be output from NE Japan volcanoes is lower (¹⁰Be < 0.8 × 10⁶ atms/g; ¹⁰Be/⁹Be <3.1 × 10^–11) than the other arcs (Kurile and Tonga-Kermadec arcs). This fact suggests that the ratio of sediment recycling at the NE Japan Arc is distinctly lower than the other cold subduction zones. The low ratio of sediment recycling is probably due to the lower temperature of descending slab beneath the NE Japan Arc than the other arcs, because cold slab induces both low extraction rate of Be from descending slab and long travel time beneath the arcs. Also, significant scraping of sediments from descending slab is another candidate to explain the low extraction rate of ¹⁰Be.

Ice core samples record information about the geological history of the Earth, including past climate changes. Dome Fuji, situated at the highest point of Queen Maud Land, is considered one of the best drilling locations for procuring samples to reconstruct past climates and environments. We present here fundamental data on the concentrations of dissolved ions in shallow samples, between 7.7 m and 65.0 m depth, from the Dome Fuji ice core drilled in 2001. The measured anions were HCOO^–, CH₃COO^–, CH₃SO₃^–, F^–, Cl^–, NO₂^–, NO₃^–, SO₄^2–, C₂O₄^2–, and PO₄^3–, and the cations were Na⁺, K⁺, Mg²⁺, Ca²⁺, and NH₄⁺. The temporal resolution of the depth profiles of the ion concentrations was less than one year. No significant correlations were observed among the ions except between Na⁺ and Cl^–. The ion balance in the core, based on the averaged ion concentrations of the samples, was different to that of sea salt, a result consistent with the findings of previous studies. In several samples, however, synchronous concentration peaks of Na⁺ and Cl^– were identified, and the Cl^–/Na⁺ ratios of the corresponding samples were close to the sea salt ratio. This observation indicates the possibility that climate conditions were such that precipitation containing sea salt occurred in the Dome Fuji area. The Cl^–/Na⁺ ratio of samples that did not exhibit Na⁺ and Cl^– peaks in the depth profile differed from that previously reported for the covering snow. This result implies that Cl^–, but not Na⁺, was redistributed after deposition. High concentrations of SO₄^2– in some samples may account for this alteration of Cl^–/Na⁺ ratios. To interpret these observations and elucidate the climatic conditions, further studies, such as isotopic analyses of δ¹⁸O and δD, are required.