Major and trace element abundances, Sr and Nd isotopic ratios, and ²³⁸U-²³⁰Th radioactive disequilibria have been analyzed for samples from five volcanoes, Oshima, Miyakejima, Niijima, Teishi Knoll and Fuji, located in the northern Izu arc to investigate across-arc and regional variations of chemical compositions of mantle and fluids expelled from a subducting slab. The abundances and abundance ratios of both fluid mobile and immobile trace elements show across-arc variations. All samples but one have radioactive disequilibria, with (²³⁸U/²³⁰Th) greater than unity (herein, a ratio in parentheses denotes the activity ratio). The observed disequilibrium is similar to those reported for other arc systems, such as Mariana, Tonga, Kermadec, Chile. It originates from higher mobility of uranium relative to thorium during dewatering of the subducting slab. The degree of radioactive disequilibrium of (²³⁸U/²³⁰Th) decreases with depth to the Wadati-Benioff zone at each volcano. The radioactivity ratios of (²³⁰Th/²³²Th) of the samples from Miyakejima, however, deviate from an across-arc trend formed by Oshima, Niijima, Teishi Knoll and Fuji. The combined data of (²³⁰Th/²³²Th)-(²³⁸U/²³²Th) of the samples from the Izu and the Mariana arc revealed a well defined array in an isochron diagram with the exceptions of the samples from Miyakejima and Alamagan. This finding requires (²³⁰Th/²³²Th) of the sub-arc mantle beneath the arcs of Izu and Mariana except the magma sources of the two islands of Miyakejima and Alamagan was around 1.1 and relatively homogeneous before the final addition of fluid from slab. The homogeneous (²³⁰Th/²³²Th) necessitates input of Th with homogeneous (²³⁰Th/²³²Th) contributed from sediment melt, which dominates the budget of Th in the sub-arc mantle. It also suggests that influence of fluid addition before the final one had not caused a variation in Th isotopic compositions of the sub-arc mantle.

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Two moss genera (Sphagnum and Polytrichum) were collected seasonally in two close (∼0.45 km distance) but environmentally different locations, an Open bog and a Spruce forest at Hala Izerska (the Izerskie Mts./SW Poland), for the stable isotope analyses of plant in-body sulfur. Simultaneously, surface water was collected in places of moss growth and along the creek discharging the bog, for stable isotope analysis of sulfate sulfur (5 locations/5 times in growing seasons). The δ³⁴S value of the analyzed mosses varies from 3.99 to 10.24‰ for Sphagnum and from 4.18 to 6.48‰ for Polytrichum. The δ³⁴S value of aqueous sulfate in creek waters, depending on location and season, ranges from 3.72 to 20.26‰. The significant correlation between the plant in-body sulfur concentration and the isotopic composition was observed for Sphagnum as well as loose correlation between δ³⁴S of sulfates in surface water and moss in-body sulfur. The fractionation factor, possibly caused by two processes of sulfate assimilation by Sphagnum and sulfate reduction by bacteria, calculated based on Rayleigh's distillation model equals about 4‰. The high correlation and simultaneous increase of δ³⁴S(SO₄^2-) and δ¹³C(DIC) values downstream the creek discharging the bog suggest that the lighter isotopes of carbon and sulfur (¹²C and ³²S) are preferentially removed, probably due to assimilation by plants. The present results imply the original signature of the source of sulfur in the environment is greatly altered by the biological activities in bog water.

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Strontium isotopic ratios, calcium and strontium contents of calcites in the eolian dust profile during the last 7 Ma at Lingtai were systematically studied. ⁸⁷Sr/⁸⁶Sr ratios of calcites change with three secondary fluctuations in the Quaternary loess-paleosol sequence: slight fluctuations from L₃₃ to S₁₅, a slight increase from L₁₅ to L₆, and a dramatic decrease from S₅ to L₁. They are usually lower in the Quaternary loess than in the interstratified paleosols. ⁸⁷Sr/⁸⁶Sr ratios of calcites in the Tertiary red clay are relatively stable, mostly higher than in the Quaternary loess and paleosols. Ca²⁺ and Sr²⁺ contents of calcites are relatively high in the Quaternary loess and the Tertiary red clay but low in the Quaternary paleosols. Sr²⁺ is well correlated with Ca²⁺, and can thus be an effective tracer for Ca²⁺. High contents of Ca (Sr) in the Tertiary red clay show that carbonates were poorly leached out of the Tertiary red clay. Like Ca contents, Ca/Sr ratios in the Tertiary red clay are close to those in the Quaternary loess. Elemental ratios and contents have different variations from the Sr isotopic ratios of calcites in the Lingtai profile, implying that isotopic ratios were better proxies for climate change than elemental ratios and contents. Primary carbonate and silicate comprised two endmembers determining the range of the Sr isotopic ratios of calcites, and chemical weathering was an inner driver to induce strontium isotopic variations of calcites in the eolian dust profile. Our isotope data indicate that chemical weathering was strongest in the Tertiary red clay, the second in the Quaternary paleosols, and weakest in the Quaternary loess. Strontium isotopic variations of calcites are in a good agreement with pedogenic characteristics in the Lingtai profile, broadly consistent with a proxy of the summer monsoon—Fe₂O₃(f)/Fe₂O₃(t) ratios, and correlate with variations of Fe²⁺/Fe³⁺ ratios in the Lingtai profile and the dust flux in ODP885/886 during the late Cenozoic. Strontium isotopic variations of calcites are different from the magnetic susceptibility records in the Lingtai profile, further demonstrating that magnetic susceptibility of the Tertiary red clay could not reliably indicate the Tertiary summer monsoon. As a result, strontium isotopic characteristics of calcites in the Lingtai profile indicate that the Quaternary summer monsoon had a glacial-interglacial alternation and weakened with large-amplitude oscillations since 0.5 Ma B.P., and also reveal that the Tertiary summer monsoon was more stable and overall stronger than the Quaternary, nevertheless, similar climates to those in the Tertiary probably occurred during a few paleosol developments of the Quaternary.

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Fluids within fault zones can change the physical and chemical properties of fault materials and have a substantial influence on faulting. Therefore it is important to understand the nature and timing of fluid migration through fault zones. In order to evaluate the timing of fluid infiltration into a deep fault zone on Awaji Island in southern Japan, we attempted to measure U-Th radioactive disequilibrium of carbonate minerals from the Nojima fault, which triggered the 1995 Kobe earthquake. Bulk carbonate samples of vein material have U concentrations of 1.2 to 2 ppm and Th concentrations of 1.6 to 6.5 ppm. The high Th abundances derived from detritus requires correction for initial ²³⁰Th in order to acquire an accurate U-Th age. Bulk carbonate samples plot near the equiline in a (²³⁰Th/²³²Th)-(²³⁴U/²³²Th) diagram, suggesting that they precipitated around or before 450 ka. Monte Carlo simulation with finite-age constraint in the IsoPlot program yields a ²³⁰Th/²³⁴U age of 486 (+380, -190) ka. The presence of radioactive disequilibrium in (²³⁴U/²³⁸U) indicates that the calcite precipitation age was younger than 1 Ma. The results of leaching experiments indicate that a leaching procedure after firing causes considerable laboratory fractionation of U and Th and does not provide usable age information.

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The Iwate-Miyagi Nairiku Earthquake in 2008 (M7.2) occurred on June 14th 2008 in the northeastern Japan, Iwate Prefecture. We collected water and gas samples in hot springs from seven localities around the epicenter of the earthquake on June 21st and 22nd, one week after the earthquake, and measured the ³He/⁴He ratio and He and Ne concentrations of the dissolved gases. We found 10-85% increases in ³He/⁴He ratios in five hot springs, while we found 11-35% decrease in two others. The positive anomalies were interpreted as upwelling of aqueous fluid containing mantle ³He beneath the earthquake region. It is possible that ascending fluids triggered the earthquake.

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