Helium isotopic ratio in Vulcano island fumaroles: temporal variations in shallow level mixing and deep magmatic supply

Intensive gas emanations occur throughout the island of Vulcano, Italy. Sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source, “crustal” waters. This mixing differs between the beach and crater fumaroles. Gas samples from three crater fumaroles with temperatures ranging from 200 to 550 ° C were sampled repeatedly over a one year period. During the same interval of time, six samples from submarine and subaerial beach fumaroles and water well gases were also sampled. Gases from one crater fumarole (F5) showed variations of (³He/⁴He)_fumarole to (³He/⁴He)_air between 5 and 6 correlated with variations of several chemical species. High ³He/⁴He ratios for the beach fluids, similar to those of crater fluids, suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs. However, temporal changes clearly indicate variable degrees of fluids mixing, and the geographic distribution of the ³He/⁴He ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs, independently related to crater and to beach fumaroles.     

Determination of Chlorine Contents in Geological Survey of Japan Reference Materials by Prompt Gamma Neutron Activation Analysis

We determined chlorine contents in nine GSJ (Geological Survey of Japan) reference materials (JB-1, 1a, 2, 3; JA-1, 2, 3; JR-1, 2) by prompt gamma neutron activation analysis, employing the standard addition method. Pressed powder disks of each reference material were used for neutron irradiation and gammaray measurement, after known quantities (25-200 μl) of sodium chloride solution were added. The influence of the nearby sodium peak overlap was checked, and fluctuations in the chlorine count rate were corrected using silicon as an internal standard. The slopes of calibration lines for seven reference materials (JB-1, 2, 3; JA-1, 2, 3; JR-2) and SiO₂ powders fall within 5% error, and their chlorine values were obtained from the intercepts. Chlorine contents in JB-1 a and JR-1 were also determined by using the calibration lines. Our chlorine values ranged from 26.1 to 934 μg g-¹, which agrees well with the previously reported values.     

Secular variations of carbon and helium isotopes at Izu-Oshima Volcano, Japan

Secular variations in ¹³C/¹²C ratios and chemical compositions of gas samples from October 1986 to July 1992 are reported from a 92–95 °C steam well located about 3 km north of Mt. Mihara, an active volcano on Izu-Oshima Island, Japan. The δ¹³C value steeply increased from −2.97‰ (relative to PDB carbonate) in December 1986 to −1.15‰ in March 1988 and then gradually decreased to −1.75‰ in July 1992. Over the same period, the CO₂ content changed similarly with time, even though the experimental error is relatively large. These variations are consistent with helium isotope changes. Initially rapid and then slow enhancements of ³He/⁴He ratio, δ¹³C value and CO₂ content are invoked by violent eruptions of Izu-Oshima volcano from 15 November to 18 December 1986. After the eruptive activity, depletion of magmatic gas emission and subsequent mixing with crustal fluids in the hydrothermal system may produce the gradual decreases of ³He/⁴He ratio, δ¹³C value and CO₂ content. Taking into account the rates of these decreases, we suggest that helium and carbon isotope ratios will return to the situation of before the magmatic eruption within 15 years.     

Isotope systematics of Li, Sr, Nd, and volatiles in Indian Ocean MORBs of the Rodrigues Triple Junction: Constraints on the origin of the DUPAL anomaly

The DUPAL anomaly, a radiogenic isotope anomaly discovered in the Indian Ocean mantle, has been interpreted as due to a large-scale mantle heterogeneity. To provide new constraints on the DUPAL origin, we analyzed isotope ratios of Li, Sr, and Nd in fresh N-MORB glasses recovered from the Rodrigues Triple Junction in the Indian Ocean, and from the North Atlantic. The Li isotopic compositions of the Indian Ocean DUPAL N-MORBs were comparable to those of the North Atlantic non-DUPAL N-MORBs. The source of the DUPAL signature in Indian Ocean MORBs and the E-MORB-type enriched mantle source have quite different Li isotopic compositions. The ¹⁴³Nd/¹⁴⁴Nd values of both sources are significantly lower than those of the North Atlantic N-MORBs. The δ⁷Li values of most oceanic island basalts with similar low ¹⁴³Nd/¹⁴⁴Nd signatures are also higher than those of the North Atlantic N-MORBs, except for several Koolau lavas. The Li isotope results support the recent proposal that significant amounts of recycled lower continental crust might produce the radiogenic isotope signatures of the Indian Ocean DUPAL source.     

Stress-induced crack path in Aji granite under tensile stress

The double-torsion test using Aji granite was carried out to investigate the interaction between stress-induced crack path and mineral grains. Crack velocities were controlled at range 10^–7 m/s to 10^–1 m/s. After the stressed specimens were dyed, we checked the crack path by thin section analysis, using an optical microscope. The stress-induced crack path was divided into two types, transgranular and intergranular cracks, and each path was subdivided with respect to mineral grains. In spite of the extensive range of crack velocities, the ratios between the transgranular and intergranular crack lengths did not change. The crack paths were all jagged, and often showed detour around the grain boundary when faced with obstacles like hard grains or preexisting cracks. That is to say, quartz grain played an important role as an obstacle. Feldspar grain could change the crack path because of its cleavage plane. Biolite grain had a serious effect on the path even if its constitution ratio is very small. Fractal dimensions of the crack paths were calculated by three methods, as indicators of surface roughness. The fractal dimensions were shown in a slight trend with the change of crack velocity. This trend can be explained from the point of limited cracking rate in stress corrosion.     

Accumulation features of trace elements in mass-stranded harbor seals (Phoca vitulina) in the North Sea coast in 2002: the body distribution and association with growth and nutrition status

Body distribution and growth- and nutritional status-dependent accumulation of 21 trace elements were investigated in harbor seals (Phoca vitulina) stranded in the North Sea coast in 2002. Higher concentrations and burdens of Mn, Se, Mo, Ag, Sn, Hg, and Bi in the liver, Cd in the kidney, As in the blubber, and Co, Sr, and Ba in the bone were observed. Significant positive correlations of hepatic Se, Mo, Ag, Cd, Sn, Hg, Tl, and Bi with standard body length were found, while significant negative relationships were detected for Mn, As, Rb, Sr, and Sb in the liver. Concentrations of Co, Se, Sr, Sn, Hg, and Bi in the liver, V, Sr, Ag, Sn, and Hg in the kidney, V, Mn, Co, Rb, Sr, Sn, Ba, and Pb in the blubber increased with decreasing blubber thickness of harbor seals, indicating enrichment of these elements in the target tissue by emaciation.     

Helium and carbon isotopes in fluorites: implications for mantle carbon contribution in an ancient subduction zone

The concentrations of helium and carbon in fluorite associated with Cretaceous to Neogene (90–13 Ma) granitic magmatism in the Japanese arc have been measured. Concentrations of Li, U, Th and Gd were measured to correct for secondary generated ³He. The CO₂/³He of fluorites are almost uniform (1.5×10¹⁰–4×10¹⁰) and in fair agreement with the range of present island arc volcanic gases. The calculated mantle C contribution in the Mesozoic subduction zone appear to have been identical to the present one (7–19%) indicating that the C flux from the mantle in supra-subduction zone environments has remained fairly constant during the past 70 million years.     

Neutron diffraction study of aluminous hydroxide δ-AlOOD

We have determined the position of deuterium atoms in δ-AlOOD by neutron powder diffraction at ambient pressure. As previously reported by theoretical and experimental studies, the deuterium atoms are located in the tunnel formed by the chains of AlO₆ octahedra. The data are best fit with the P2₁ nm structure, producing bond lengths of D–O1 of 1.552(2) Å, O2–D of 1.020(2) Å and O1–O2 of 2.571(2). This study confirms that the hydrogen bond is asymmetric at ambient conditions in agreement with recent single-crystal synchrotron study for δ-AlOOH.     

Multi-approach characterization of shallow-water carbonates off Minamitorishima and their depositional settings/history

Sedimentological, geochemical, and chronological analyses were carried out on 18 carbonate rock samples collected at depths of 938, 1085, and 3354 m on the western slope of Minamitorishima (Marcus Island), which is located near the western margin of the Pacific Plate. Four groups of carbonate rocks were distinguished: a mollusk-rich limestone, a coral-rich dolomite, a foraminiferal-nannofossil packstone, and a phosphatized mudstone/wackestone. The mollusk-rich limestone is characterized by the dominance of bivalves (including rudists) and gastropod shells. Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) and Mesorbitolina ex gr. texana (a large benthic foraminifer) indicate that the shallow-water carbonates were deposited during the late Aptian–early Albian (ca. 123–111 Ma). The coral-rich dolomite is characterized by abundant scleractinian corals and nongeniculate coralline algae associated with encrusting acervulinid foraminifers. The biotic composition is similar to that of the Oligocene–Pleistocene carbonates reported from other seamounts in the northwestern Pacific. Geochemical data show that the coral-rich carbonates were dolomitized at 9.5–6.8 Ma (Tortonian–Messinian) and that normal seawater was the most likely parent fluid. The foraminiferal-nannofossil packstone is a semi-consolidated foraminiferal-nannofossil ooze and was deposited during the Pleistocene (0.99–0.45 Ma). The phosphatized mudstone/wackestone is marked by the absence of macrofossils and the presence of traces of planktic foraminifers. Although its depositional age is not constrained, the Sr isotope ratios indicate that the phosphatization occurred at 33.2–28.9 Ma. After the deposition of the Cretaceous shallow-water carbonates, including the mollusk-rich limestone, Minamitorishima was drowned and its top was covered with a pelagic cap, represented by the mudstone/wackestone. The late Eocene–early Oligocene volcanism (40.2–33.2 Ma) caused episodic uplift and returned the top of Minamitorishima to a shallow-water environment. After the early Oligocene phosphatization of the pelagic cap, coral reefs flourished on the top of this island. The reef limestone was dolomitized during the Tortonian–Messinian.