Sulfur Isotope Study on Hg and Sb Deposits in Japan

Abstract. Sulfur isotope ratios of cinnabar from Hg deposits and stibnite, jamesonite and berthierite from Sb deposits in Japan are examined in order to understand metallogeneses of Hg and Sb deposits in Japanese island arcs. The studied Hg and Sb deposits include the Hg deposit at Yamato‐suigin (Honshu) and the Sb deposit at Ichinokawa (Shikoku) in the Southwest Japan arc. In addition, Hg deposits including Itomuka and Ryushoden in central Hokkaido and Hg and Sb mineralizations in Northeast Japan arc are examined. The δ³⁴S values of cinnabar from the Hidaka‐Kitami district, central Hokkaido, including the Itomuka and Ryushoden deposits range widely, from ‐10 to +16 %o, the highest values encountered at the Samani deposit. The δ³⁴S values of cinnabar from other areas in Japan range from ‐12 to +5 %o, having δ³⁴S values higher than +2 %o from southwestern Hokkaido (Meiji deposit), Shikoku (Suii deposit) and Kyushu (Hasami and Yamagano deposits). On the other hand, the δ³⁴S values of stibnite from all areas in Japan range from ‐14 to +5 %o, having positive δ³⁴S values higher than +2 %o up to +5 %o from southwestern Hokkaido (Yakumo, Toyotomi and Teine deposits) and eastern‐central Honshu (Hachiman and Daikoku deposits). The variation in δ³⁴S values of Hg and Sb deposits may reflect the variation in δ³⁴S values of country rocks or variation in mixing ratio of sulfur extracted from the country rocks, sulfur derived from seawater sulfate, and sulfur derived from magmatic emanations. The relatively high δ³⁴S values of cinnabar and stibnite higher than +2 %o from southwestern Hokkaido, eastern‐central Honshu and Kyushu are probably caused by contribution of volcanic emanation from arc magmas having positive σδ³⁴S values, whereas the positive δ³⁴S values of cinnabar higher than +2 %o from Suii deposit in Shikoku may be attributed to structurally substituted sulfate in limestone country rocks and/or sulfur derived from seawater sulfate. However, the wide range of the δ³⁴S values of cinnabar from the Hidaka‐Kitami district, central Hokkaido, is difficult to explain at this moment. Other relatively low, negative δ³⁴S values of cinnabar and stibnite, berthierite from other areas in Japan may be attributed to 1) incorporation of isotopically light sedimentary sulfur or sulfur derived from ilmenite‐series silicic magma, or 2) less contribution of volcanic emanation from arc magmas having positive σδ³⁴S values.     

A THEORETICAL STUDY ON THE MULTIPLE EQUILIBRIA OF TROPICAL ATMOSPHERE AND THEIR RELATION TO THE ONSET OF THE SUMMER MONSOON

Multiple equilibria and their stability in tropical atmosphere are investigated through β-plane barotropic models with consideration of heating and dissipation. We have derived the solutions of the model equations corresponding to the multiple equilibria or the steady flows first, and then establish the criteria for the stability of steady flow by use of the Liapunov direct Method. When these criteria are applied to the solutions of equilibria obtained, stable flows, which are closely related to the different patterns of quasi-stationary circulation in the tropical region, are found. The configurations of these stable flows and the shift between two of them as season changes provide quite reasonable explanations to many fundamental problems of tropical circulation features such as the catastrophe mechanism of the onset and the break-active cycle of the Asian summer monsoon. It follows that the onset or the abrupt transition of the Asian summer monsoon could be attributed to the multiple equilibrium property of the tropical circulation resulted from the advective nonlinearity, which provide another explanation among others.     

High‐pressure polymorphs in Yamato‐790729 L6 chondrite and their significance for collisional conditions

Shock pressure recorded in Yamato (Y)‐790729, classified as L6 type ordinary chondrite, was evaluated based on high‐pressure polymorph assemblages and cathodoluminescence (CL) spectra of maskelynite. The host‐rock of Y‐790729 consists mainly of olivine, low‐Ca pyroxene, plagioclase, metallic Fe‐Ni, and iron‐sulfide with minor amounts of phosphate and chromite. A shock‐melt vein was observed in the hostrock. Ringwoodite, majorite, akimotoite, lingunite, tuite, and xieite occurred in and around the shock‐melt vein. The shock pressure in the shock‐melt vein is about 14–23 GPa based on the phase equilibrium diagrams of high‐pressure polymorphs. Some plagioclase portions in the host‐rock occurred as maskelynite. Sixteen different CL spectra of maskelynite portions were deconvolved using three assigned emission components (centered at 2.95, 3.26, and 3.88 eV). The intensity of emission component at 2.95 eV was selected as a calibrated barometer to estimate shock pressure, and the results indicate pressures of about 11–19 GPa. The difference in pressure between the shock‐melt vein and host‐rock might suggest heterogeneous shock conditions. Assuming an average shock pressure of 18 GPa, the impact velocity of the parent‐body of Y‐790729 is calculated to be ~1.90 km s^?1. The parent‐body would be at least ~10 km in size based on the incoherent formation mechanism of ringwoodite in Y‐790729.     

Topotaxic relationships between spinel and pyroxene in kelyphite after garnet in mantle-derived peridotites and their implications to reaction mechanism and kinetics

Kelyphite is a reaction product between garnet and olivine, which was formed by subsolidus reactions upon decompression during the ascent of mantle peridotite. We studied crystallographic relationships among constituent (product) phases of kelyphite ?C orthopyroxene, clinopyroxene, spinel and reactant phases, garnet and olivine, using EBSD and found that, for a relatively high temperature sample (from Czech Moldanubian), spinel and pyroxenes are in a topotaxic relationship in such a way that spinel {111} coincides with pyroxene (100) and spinel {110} coincides with pyroxene (010); while the topotaxy is incomplete or non for a lower-temperature sample (from western Norway). On the basis of the observed microstructural and crystallographic relationships, we propose a hypothesis that the topotaxic relationship may be established at nucleation stages of the onset of the kelyphitization and that the degree of topotaxy may be related to the transformation temperature and the degree of supersaturation of the reaction. The lower the temperature, the higher the supersaturation and, therefore, more rapid the nucleation becomes, resulting in a more disordered state in topotaxic relationship.     

River Water Pollution in Developed and Developing Countries: Judge and Assessment of Physicochemical Characteristics and Selected Dissolved Metal Concentration

To compare water quality in rivers of developed and developing countries, a study based on physicochemical parameters and dissolved metals levels was conducted. Water samples were collected from selected sites in Dhaka, Bangladesh; Hokkaido and Osaka, Japan; Erdenet, Mongolia and West Java, Indonesia. Analysis of least significant differences revealed that most water quality parameters were within comparable low levels in both developed and developing countries. The dissolved metals concentrations were found to be similar and below those of water standards except for manganese and cadmium at every sampling point, and lead in Erdenet, Mongolia. Some metals showed high enrichment factors in the rivers of Osaka, Japan and Erdenet, Mongolia, indicating accumulation possibility of metals in the river‐bed sediments. High concentrations of dissolved organic carbon, Escherichia coli and dissolved metals suggested greater water pollution in some rivers of developing countries than in the rivers of Japan. Principal component analysis showed strong correlations between “dissolved organic carbon and chemical oxygen demand” and “conductivity and total dissolved solids” at each sampling point, and E. coli, nitrate (NO), nitrite (NO), and pH levels were found to be higher in the rivers of Dhaka and Erdenet. In addition, there were high levels of Al and Zn in West Java, Pb in Erdenet, and Mn, Fe, and Cr in the rivers of Dhaka and Japan. Based on pressures and impacts, it is evident that dissolved metal, organic, and fecal pollution in the rivers of developing countries are in somewhat dreadful condition in comparison with the rivers of developed country.     

Fe–Mg partitioning between post-perovskite and ferropericlase in the lowermost mantle

Fe–Mg partitioning between post-perovskite and ferropericlase has been studied using a laser-heated diamond anvil cell at pressures up to 154 GPa and 2,010 K which corresponds to the conditions in the lowermost mantle. The composition of the phases in the recovered samples was determined using analytical transmission electron microscopy. Our results reveal that the Fe–Mg partition coefficient between post-perovskite and ferropericlase (K _D^PPv/Fp) increases with decreasing bulk iron content. The compositional dependence of K _D^PPv/Fp on the bulk iron content explains the inconsistency in previous studies, and the effect of the bulk iron content is the most dominant factor compared to other factors, such as temperature and aluminum content. Iron prefers ferropericlase compared to post-perovskite over a wide compositional range, whereas the iron content of post-perovskite (X _Fe^PPv, the mole fraction) does not exceed a value of 0.10. The iron-rich ferropericlase phase may have significant influence on the physical properties, such as the seismic velocity and electrical conductivity at the core–mantle boundary region.     

Characteristics and Mineralization Age of the Fukusen No. 1 Vein,Hishikari Epithermal Gold Deposits,Southern Kyushu,Japan

The Fukusen No. 1 vein is located in the southeastern part of the Yamada deposit, Hishikari epithermal gold deposits, southern Kyushu, Japan. ⁴⁰Ar/³⁹Ar plateau ages of adularia from the margin and the center of the Fukusen vein are determined to be 0.617 ± 0.024 Ma and 0.606 ± 0.009 Ma, respectively. The Fukusen No. 1 vein shows banding structure composed mainly of quartz, adularia and clay minerals. Colloform texture is displayed by cryptocrystalline to amorphous silica material that is associated with fine-grained electrum and sulfides near the center of the vein. Pyrite in the Fukusen No. 1 vein often shows acicular shape resulting from inversion from marcasite. Near the center of the vein, primary marcasite occurs associated with colloform texture of silica. The Fukusen No.1 vein preserves primary texture and materials which were deposited from the ore-forming hydrothermal solution. The Fukusen No. 1 vein was formed in a short period and is one of the youngest veins in the Hishikari deposits.     

Winter Oceanographic Conditions in the Southwestern Part of the Okhotsk Sea and Their Relation to Sea Ice

In the southwestern part of the Okhotsk Sea, oceanographic and sea-ice observations on board the icebreaker Soya were carried out in February 1997. A mixed layer of uniform temperature nearly at the freezing point extending down to a depth of about 300 m was observed. This is much deeper than has previously been reported. It is suggested that this deep mixed layer originated from the north (off East Sakhalin), being advected along the shelf slope via the East Sakhalin Current, accompanied with the thick first-year ice (average thickness 0.6 m). This vertically uniform winter water, through mixing with the surrounding water, makes the surface water more saline (losing a characteristic of East Sakhalin Current Water) and the water in the 100–300 m depth zone less saline, colder, and richer in oxygen (a characteristic of the intermediate Okhotsk Sea water). The oceanographic structure and a heat budget analysis suggest that new ice zone, which often appears at ice edges, can be formed through preconditioning of thick ice advection and subsequent cooling by the latent heat release due to its melting. This revised version was published online in August 2006 with corrections to the Cover Date.     

Coastal polynyas off East Queen Maud Land observed from NOAA AVHRR data

Coastal polynyas off East Queen Maud Land in Antarctica are examined using NOAA AVHRR infrared data. From image analyses, two locations of coastal polynyas in this region are identified; one in Breid Bay and the other along the shelf break. The areal coverage of the Breid Bay polynya is significantly related to the strength of katabatic winds, which maintain their strength over the coastal sea due to land topography favoring for their confluence, thereby being capable of removing newly formed ice. Land fast ice in the eastern part of the bay also plays an additional role in the formation mechanism. It is also found that the areal coverage of coastal polynyas in this region fluctuate coherently. Moreover, these fluctuations correspond to the synoptic index, which measures the strength of the offshore wind, with their peaks closely associated with the areal peaks. These facts strongly suggest the influence of synoptic scale weather on the formation and maintenance of polynyas in this region.     

MIS11–19 pollen stratigraphy from the 250-m Choshi core, northeast Boso Peninsula, central Japan: Implications for the early/mid-Brunhes (400–780 ka) climate signals

Abstract   The 250-m Choshi core (CHOSHI-1), drilled from hemipelagic muds of the Inubo Group, has been physically, geochemically and tephrochronologically analyzed back to 1 Ma. We provide pollen results for the 19–169 m section of the core (400–780 ka) bracketed by the marker tephra Ty1 (equivalent to J4) and the Brunhes–Matuyama paleomagnetic boundary. The results show good agreement with the corresponding oxygen isotope (δ¹⁸O) profile, with high δ¹⁸O intervals dominated by boreal conifers Picea , Abies , Pinus (subgen. Haploxylon ) and Tsuga ( diversifolia ), whereas low δ¹⁸O intervals are dominated by temperate conifers Cryptomeria , Taxaceae-Cephalotaxaceae-Cupressaceae and Sciadopitys . In order to confirm pollen-climate relations for the relevant taxa, a modern surface pollen dataset for the Japanese archipelago was consulted. In this analysis, the ratios of Cryptomeria / Picea and temperate/boreal conifers serve as proxies for the 100-kyr glacial/interglacial cycle during the Middle Pleistocene. Distinct signals for marine isotope stages (MIS) 11, 12, 13–15, 16, 17 and 18–19 are recognized in accordance with the tephrochronology and δ¹⁸O of the same core. Application of the criteria to an independent pollen record from Lake Biwa provides an integrated pollen stratigraphy for mid-latitude Japan during the past 800 ky. Some degree of uncertainty remains in the chronology of the MIS13–15 interval, relating to the uncertainty in the eruption age of widespread tephra Ks11.