The area that is located in the Tertiary Gampo basin is mainly composed of Cretaceous shale, Tertiary rhyolite, granite, and basalt in ascending order. The mineralogy, isotopic composition (δD and δ¹⁸O) of clay minerals, and chlorite geothermometry were performed to interpret the alteration history of these rocks. Clay minerals occurring in basalt have a limited range and are heavier in δ¹⁸O than the clay minerals in granite and rhyolite. Chlorite occurring in basalt has lower formation temperatures than chlorite in granite or rhyolite. Geochemical studies were carried out to identify the behaviors of major, trace and rare earth elements (REE) during alteration processes. Most major oxides such as SiO₂, Al₂O₃, Fe₂O₃, Na₂O, MgO, TiO₂, MnO, and P₂O₅ of basalt are relatively immobile in most altered zones. In contrast, these oxides in granite and rhyolite are relatively mobile, and show some irregular variations in the most altered zones. Some trace elements in basalt have less prominent variations than in granite and rhyolite. REE distributions of altered basalt and granite do not show prominent variations with increasing alteration degree, whereas rhyolite is enriched in REE and has a positive Eu anomaly. These results indicate that altered basalts that have experienced only low temperature alteration such as weathering, have indistinct variations of major oxides, some trace elements and REE according to alteration intensity. Granite and rhyolite that have experienced both hydrothermal alteration (low temperature) and weathering process are characterized by relatively prominent variations of major oxides, some trace elements and REE according to alteration intensity. The results coincide well with those of mineralogical studies, isotopic compositions of clay minerals, and chlorite geothermometry.

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The presence of highly siderophile elements (Ru, Rh, Pd, Re, Os, Ir, Pt, and Au) in the mantle has been a long standing enigma in the Earth sciences. Highly siderophile elements exhibit extremely low silicate/metal partition coefficients and so should have partitioned into the core, leaving the mantle depleted and fractionated compared with precursor material. Late accretion of undifferentiated material after completion of core formation may have overprinted the residue inherited from metal-silicate equilibrium partitioning. Here, we present a model based on the osmium isotopic composition of the mantle that sheds new light on the distribution of highly siderophile elements in Earth. As the Earth grew from the accretion of chondritic material of unspecified nature, gravitational and radioactive heating permitted early segregation of metal from silicate. This resulted in fractionation of highly siderophile element abundances in the residual mantle relative to chondritic abundances. After completion of core formation, the model supposes that a late carbonaceous veneer delivered biogenic and highly siderophile elements to the Earth. This late veneer was mixed inhomogeneously with the fractionated residue left over after core formation. Part of the deep mantle was isolated early from shallow convection and thus preserved primordial noble gas and highly siderophile element signatures. In this scenario, the contrast between the ¹⁸⁷Os/¹⁸⁸Os ratio of the carbonaceous late veneer and that of fertile lherzolites places strict constraints on the coupled silicate/metal partition coefficients of Re and Os (D^Re = 1.6 ± 1.2 × 10^-4 + D^Os). Similarly, the high ¹⁸⁷Os/¹⁸⁸Os and ¹⁸⁶Os/¹⁸⁸Os ratios observed in certain plumes impose restrictions on the coupled silicate/metal partition coefficients of Pt and Os (D^Pt = 8.0 ± 6.2 × 10^-4 + D^Os)

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Major and trace element and Nd-Sr isotopic data are presented on the granitic rocks known as a basement in the Cheju volcanic island, together with CHIME age data on porphyritic hornblende-biotite granite xenolith from the Byeoldobong area. The CHIME ages from zircon and allanite grains of porphyritic hornblende-biotite granite were determined to be 169 ± 29 Ma and 183 ± 40 Ma, respectively, which are corresponding to a Jurassic age. It is concordant with a K-Ar age of 172.4 ± 5.2 Ma of a biotite granite in the same area, which is comparable to the Daebo granite in the Korean peninsula. Granitic xenoliths from the Byeoldobong area have Nd-Sr isotopic compositions (initial ratio (¹⁴³Nd/¹⁴⁴Nd)i = 0.51156∼0.51158, ε_Nd = −19∼−14 and (⁸⁷Sr/⁸⁶Sr)i = 0.7156∼0.7164, ε_Sr = 101∼179) which are close to those of Jurassic Daebo granite (ε_Nd = −21∼−14, ε_Sr = 104∼171). On the other hand, the micrographic granite from the drilling core in the Hadeokcheon area gives initial ratio (¹⁴³Nd/¹⁴⁴Nd)i = 0.51218 and (⁸⁷Sr/⁸⁶Sr)i = 0.7077), which are comparable to the Cretaceous Bulguksa granite ranging from 0.51184 to 0.51268 in ¹⁴³Nd/¹⁴⁴Nd and 0.7055 to 0.7167 in ⁸⁷Sr/⁸⁶Sr. The T^Nd_DM model ages of 1.0 to 1.7 Ga from the Mesozoic granitic plutons in the Cheju island suggest that the source materials of the plutons in the island have evolved since mid-Proterozoic time as those of the peninsula. In combination with the basement geology and petrochemistry, Nd-Sr isotopes, and radiometric and model ages of granitic rocks, our results imply that the Okchon zone is continuously extended to the Cheju volcanic Island of the southeastern end of the continental margin of the Eurasian plate.

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REE and other trace elements in altered and unaltered phyllites, orebodies and quartz veins in the Yinshan deposit were determined in order to examine behaviors of trace elements during hydrothermal alteration. REE, especially LREE, were selectively leached from the phyllites that had been undergone recrystallization dominantly of the major minerals during hydrothermal alteration. The greater the degree of alteration was, the stronger the leaching of REE would be. LREE were leached from the rocks that are close to the intrusions and re-deposited in the part far away from the intrusions. Nevertheless, Eu was systematically leached from the rocks, resulting in strong negative Eu anomalies in the altered phyllites. The lower total REE contents in the altered rocks close to the intrusions, compared to those from the further part is probably attributed to the dilution of REE-barren minerals (quartz and sulfides), and the removement of REE from the rocks by hydrothermal alteration. REE in the hydrothermal solutions are characterized by enrichment in LREE, strong positive Eu anomalies and (La/Yb)_N ratios much smaller than those of the phyllites. The addition of REE from the hydrothermal solutions into the altered rocks resulted in the observed smaller (La/Yb)_N ratios in the altered phyllites than that of the unaltered equivalent. For other trace elements, Y behaved similarly to HREE. The LIL elements such as Rb, Sr and Ba behaved differently, which may be attributed to the different fates of their main hosting minerals. The ore-forming elements such as Cu, Pb, Zn, Ag and Sn were remarkably added to the altered phyllites, while Hf, Th, U, Nb, and Zr remained rather constantly during hydrothermal alteration. It is suggested by the REE features that ore-forming fluids probably found their ways upwards from the depth through faults to the locus of ore deposition. The degree of REE mobility increases with the sizes of the orebodies. Thus, REE is probably an effective geochemical indicator for distinguishing between small and large orebodies at the later stage of exploration.

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The radioactive disequilibrium measurements between ²³⁸U and ²³⁰Th with a Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS) were applied to igneous standard rocks distributed by Geological Survey of Japan and Geological Survey of the United States. We modified sample dissolution and Th separation method, as well as Th isotope analysis by MC-ICPMS described by Nakai et al. (2001). High sensitivity of our ICP-MS enabled to analyze less than 10 ng Th. The abundances of U and Th were determined by an isotope dilution method, using a ²³⁵U depleted uranium reagent and ²³⁰Th prepared by milking of natural U as spikes. We can determine ²³⁸U/²³²Th abundance ratio with a precision of about 2%. This procedure was applied to (²³⁸U/²³⁰Th) radioactive disequilibrium measurements of igneous standard rock samples. Samples older than 350 Ka were found to attain secular equilibrium, indicating the accuracy of our analysis. On the other hand, young igneous standard rocks were found enriched in ²³⁸U relative to ²³⁰Th, (²³⁸U/²³⁰Th)_{activity ratio} > 1, which is often observed for igneous rocks from subduction zones.

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In order to obtain the mineralization ages of the Dongchuan Copper Deposits, two quartz samples and a siliceous breccia were analyzed using the ⁴⁰Ar-³⁹Ar technique by crushing in vacuum and then by stepped heating of the powders of two of them. The results indicate that the vein-type copper mineralizations took place 780∼700 Ma ago and further show that the ⁴⁰Ar-³⁹Ar technique by crushing is an effective, widely-applicable and promising dating method for the mineralization ages of the hydrothermal deposits. The mineralization ages are in good agreement with the ages of the widely distributed magmatic rocks in the South China, which means that the pulses of anorogenic magmatic activities during the period of the breakup of Rodinia (Park et al., 1995; Li, Z. X. et al., 1999, 2002; Li, X. H. et al., 2002) were accompanied by the copper mineralizations in Dongchuan. Strong differences between the results of the crushing and heating experiments of two samples imply that the gases released by crushing were mainly from the fluid inclusions and those by heating were from the minerals of the samples, which is supported by microscopic observations of the thin sections and the results of EPMA and XRD analyses.

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We present isotopic analyses of helium in fluids collected during two field trips at Satsuma-Iwojima and Shin-Iwojima islands in November 1998 and October 2000. These are the first reported helium measurements at Shin-Iwojima. Copper tubes tightly closed by clamps at both ends were used to sample 1) gases from high and low temperature fumaroles in the summit area of Iwodake cone, 2) gases from a fumarole on Shin-Iwojima, 3) gas bubbling from the sea-floor along Shin-Iwojima where an increasing bubbling intensity was observed between 1998 and 2000, 4) waters from Sakamoto and Higashi hot springs. For gas samples, two types of correction for atmospheric contamination are discussed, using either the neon concentration or just the partial pressure of condensable gases at liquid nitrogen temperature; this latter method turned out to be very efficient for many samples. For all gas samples, we found ³He/⁴He isotopic ratios between 7.1 and 8.2 times the atmospheric ratio, pointing to a magmatic origin for fumaroles both at Iwodake crater and at Shin-Iwojima island. Our measurements show a decrease of the isotopic ratios at Iwodake with decreasing temperature of the fumarole. Comparing the results of both field trips and those published in previous studies, we suggest this volcanic system is undergoing a recent increase of activity.

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Trace, Rare Earth Element (REE), Rb-Sr and Sm-Nd isotope analyses have been carried out on selected basic-ultrabasic rocks of Dhanjori volcanic belt from the Eastern Indian Craton (EIC). The Sm-Nd isotopic data of these rocks yield an isochron age of 2072 ± 106 Ma (MSWD = 1.56). Chondrite normalized REE plots display shallow fractionated REE pattern with LREE enrichment. In primitive mantle normalized plots also these rocks show shallow fractionated pattern with depletion of Nb and Ba and enrichment of LILE like Rb, Th and U. Depletion of Nb, Ba and Zr and enrichment of Rb, Th and U are found in N-MORB normalized plots as well. Compatible elements like Tb, Y and Yb on the other hand, show a flat pattern. Isotope, trace and REE modelling indicate that these were produced by 3–5% partial melting of a spinel lherzolite source. The Nd isotopic data suggest that an enriched (ε_Nd = −2.4) mantle existed below the Dhanjori basin during ∼2.1 Ga. The enrichment was possibly caused by continuous recycling of the earlier crust into the mantle whereby subducted slab derived fluid modified the surrounding mantle. The process also affected the more easily susceptible Rb-Sr systematics producing variable Sr_i (0.702–0.717). The enriched mantle material, part of a thermal plume, pierced through the deep fractures produced due to the cooling and readjustment of the Archaean continental crust and ultimately outpoured within the Dhanjori basin. The plume magmatism was manifested by the extrusion of komatiitic/basaltic flows and basic/ultrabasic intrusives. The residence time of the plume within the upper mantle was possibly very small as no depleted signature (even in Nd isotope) has been obtained. This means a deep plume was fed by a recycled oceanic crust via globally extensive subduction process, already initiated by the end-Archaean period.

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The Kinan Seamount Chain lies close to the extinct spreading center of the Shikoku Basin, one of the largest marginal basins in the western Pacific region. Geochemical and isotopic analyses reveal that basalts from the Kinan Seamount Chain have the following characteristics that differ from the Shikoku Basin tholeiite: 1) more incompatible emelent enriched compositions, 2) lower abundance of the heavy rare earth elements (HREE), and 3) higher ⁸⁷Sr/⁸⁶Sr and lower ¹⁴³Nd/¹⁴⁴Nd ratios. These results indicate: 1) a more enriched mantle source for basalts from the Kinan Seamount Chain, 2) existence of clinopyroxene and/or amphibole in their residual mantle, and 3) mixing of magmas from a normal MORB source with the EMI signature and an ocean-island basalt (OIB) source with the EMII signature; and 4) the latter has a more significant contribution to the Kinan Seamount Chain basalts than the Shikoku Basin tholeiite.

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