Uranium and thorium diffusion in diopside

This paper presents new experimental data on the tracer diffusion rates of U and Th in diopside at 1 atm and 1150–1300°C. Diffusion couples were prepared by depositing a thin layer of U–Th oxide onto the polished surface of a natural diopside single crystal, and diffusion profiles were measured by ion microprobe depth profiling. For diffusion parallel to [001] the following Arrhenius relations were obtained: log₁₀D_U=(−5.75±0.98)−(418±28 kJ/mol)/2.303RT log₁₀D_Th=(−7.77±0.92)−(356±26 kJ/mol)/2.303RT. The diffusion data are used to assess the extent to which equilibrium is obtained during near fractional melting of a high-Ca pyroxene bearing mantle peridotite. We find that the diffusion rates for both elements are slow and that disequilibrium between solid and melt will occur under certain melting conditions. For near-fractional adiabatic decompression melting at ascent rates >3 cm/yr, high-Ca pyroxene will exhibit disequilibrium effects. High-Ca pyroxene will become zoned in U and Th and the melts extracted will be depleted in these incompatible elements relative to melts produced by equilibrium fractional melting. U and Th diffusivities in high-Ca pyroxene are similar, and diffusive fractionation of these elements will be limited. Numerical solutions to a dynamic melting model with diffusion-controlled chemical equilibration indicate that the activity ratio [²³⁰Th/²³⁸U] in a partial melt of spinel peridotite will be slightly less than 1 for a broad range of melting parameters. This result reinforces the already widely accepted conclusion that melting of spinel peridotite cannot account for ²³⁰Th excesses in mid-ocean ridge and ocean island basalts, and that garnet must therefore be present over part of the melting column.     

Strain geometries in the Sanbagawa Metamorphic Belt inferred from deformation structures in metabasite

Abstract Ductile deformation in the Sanbagawa Metamorphic Belt has been considered to be characterized by uniaxial elongation parallel to the east–west‐trending lineation, based on strain analysis of radiolarian fossils in metachert. However, only limited data were available to test this idea in strongly recrystallized schists. Strain measurements on deformed pillow structures in central Shikoku show uniaxial flattening, whereas pressure shadows around pyrite in the Kanto Mountains indicate constrictional strain. In addition, in the low‐grade part of the Sanbagawa Metamorphic Belt belonging to the Northern Chichibu Belt in the Kanto Mountains, deformed amygdules in pillow lava show flattening strain, which is consistent with the results of strain measurements using radiolarian fossils in the same area. These observations, together with the results of other strain analyses reported so far, indicate that the strain field is not uniform and that the east–west‐trending shearing and stretching were not pervasive in the Sanbagawa Metamorphic Belt.     

Trace element zoning in garnet from the Kwoiek Area,British Columbia: disequilibrium partitioning during garnet growth?

Trace element zoning in garnets from two contact-metamorphosed rocks from the Kwoiek area, British Columbia (Hollister 1969a), was measured with an ion microprobe. Zoning profiles have three distinct parts with chemical breaks defined by co-variation of major and trace elements. Important features of the trace element zoning profiles are: (1) roughly bell-shaped zoning profiles for Y and the HREEs, (2) an abrupt increase in Ti at a point midway through each garnet with inflections in the zoning profiles of other elements (Li, Na, Cr, V, Y, Zr, and the HREE), and (3) irregular Cr and V profiles. Unlike Mn zoning, the zoning profiles of most other trace elements cannot be easily modeled using simple Rayleigh fractionation models. Ti activity in the two samples is buffered by phase relations with ilmenite. Garnets from a continuously heated contact metamorphic environment should display continuous Ti zoning profiles if equilibrium was maintained and provided the Ti buffering assemblage did not change during garnet growth. The irregular Ti profiles suggest disequilibrium behavior. Several elements (Cr, V) may indicate breakdown of a phase enriched in trace elements during metamorphism. The source for the mass excess of these elements is probably the refractory cores of ilmenite grains. Either differing matrix transport rates of trace lements or interface kinetic controlled segregation could explain the unusual trace element behavior at the element inflection point. The preferred explanation involves segregation of elements at the interface of the garnet that were trapped during episodes of rapid garnet growth.     

Formation Process of North Pacific Intermediate Water Revealed by Profiling Floats Set to Drift on 26.7 σθ Isopycnal Surface

Six newly developed floats, which were set to drift on the 26.7 σ_θ isopycnal surface and to profile temperature, salinity and pressure above 1000 dbar once a week, were deployed in the Oyashio and Kuroshio Extension (KE) in order to examine the circulation, formation site and time scale of newly formed North Pacific Intermediate Water (NPIW). The floats were deployed in February or May 2001, and the data from their deployments to December 2002 are analyzed here. Four of the six floats were deployed near the KE axis at around the first meander crest, and they moved eastward to 157°E–176°W at latitudes of 30°N–45°N. The other two floats deployed in the Oyashio water with low-potential vorticity near the south coast of Hokkaido moved southward to reach the KE front and then moved eastward to the same region as the first four floats. The temperature and salinity at 26.7 σ_θ measured by the profiling floats indicate that the source waters of NPIW, Oyashio and Kuroshio waters are drastically mixed and modified in the mixed water region west of 160°E. The floats were separated into the three paths east of 160°E between the Kuroshio Extension front and the north of Water-Mass front (nearly subarctic front). New NPIW is judged to be formed along these three paths since the vertical profiles of temperature and salinity are quite smooth, having a salinity minimum at about 26.7σ_θ along each path. Kuroshio-Oyashio isopycnal mixing ratios of the new NPIW are 7:3, 6:4 and 5:5 at 26.7σ_θ along the southern, middle and northern paths, respectively. Potential vorticity converges to about 14–15 × 10⁻¹¹ m⁻¹s⁻¹ along these paths. The time scale of new NPIW formation is estimated to be 1–1.5 years from the merger of Oyashio and Kuroshio waters to the formation of the new NPIW. This revised version was published online in July 2006 with corrections to the Cover Date.     

Measurements of the Turbulent Energy Dissipation Rate around the Shelf Break in the East China Sea

Using the micro-structure profiler, TurboMAP, large values for the turbulent energy dissipation rate ε were found just above the bottom of the shelf and around the thermocline near the continental shelf break in the East China Sea. The values found above the bottom are produced by the bottom stress due to tidal currents, resulting in a distinct bottom mixed layer where the vertical eddy diffusivity Kz is also large. Distinct maxima in the values of ε detected around the thermocline are located at the depth of the fine-scale shear maxima detected with the moored ADCP. The vertical profiles of ε were compared with those of the current velocity, and it was found that the maxima in ε appear to correspond to those of the shear with fine scale. The magnitude of the observed ε coincided approximately with the ε calculated from the fine-scale shear and the buoyancy frequency according to the parameterization proposed by Gregg (1989), if the large-scale mean shear caused by the Kuroshio is subtracted. However, it is not clear whether the parameterization for the internal wave fields in the open ocean is applicable to the estimation of ε in the shelf break. Whereas the most predominant value of ε was found just above the bottom and around the thermocline, the maxima of ε could be found in the internal area. They could have been caused by the propagation of the vertically high wave number internal tides along the characteristic ray.     

日本北海道Koryu矿山浅成低温热液Au-Ag矿化的成因

Koryu矿山位于北海道南西部,为一浅成低温热液型Au-Ag石英脉型矿床.矿床产于中新世黑色泥岩中的东西向剪切带内.矿床含有8个主要脉体,总体呈东西走向,在水平、垂直方向上均发生结构、构造的变化.1号脉和3号脉中冰长石K-Ar年龄为0.8~1.2 Ma,表明矿化时代为更新世.根据矿脉体的穿插关系和脉内矿物共生关系得出矿区有2期矿化,早期矿化可分3个阶段（即E-Ⅰ,E-Ⅱ,E-Ⅲ）,晚期矿化可分成7个阶段（即L-Ⅰ,L-Ⅱ,L-Ⅲ,L-Ⅳ,L-Ⅴ,L-Ⅵ,L-Ⅶ）.宽矿脉体由多阶段矿化组成,Au-Ag矿化主要与L-Ⅲ阶段矿化密切相关.早期矿化形成的特征矿物为钙菱镁矿、钙锰辉石及少量矿石矿物;晚期矿化形成大量矿石矿物.含AuAg的矿物主要为银金矿、螺状硫银矿-辉硒银矿、硫锑铜银矿-硫砷铜银矿、浓红银矿-淡红银矿、辉铜银矿、马硫铜银矿、碲银矿和黝铜矿.而脉石矿物为绿泥石、蒙脱石、石英.区内许多成矿阶段均含富气相流体包裹体,这表明沸腾作用在整个过程中间歇发生.早期矿化温度（263~283℃）稍高于晚期矿化温度（246~260℃）.成矿溶液盐度为0.5%~6.0% NaCl当量,尽管CO₂含量在晚期矿化阶段达0.4%（质量分数）.这些特征表明成矿流体最大压力为3.1~6.8 M Pa,相当于古潜水面下430~850 m深度.石英形态学结合流体包裹体研究证实流体沸腾作用反复发生,导致SiO₂过饱和,形成结构各异的二氧化硅矿物.在脉体形成过程中,SiO₂重结晶形成石英.稳定同位素资料、矿物共生组合特征、石英结构特征和流体包裹体特征综合研究得出Koryu金-银矿床成矿模式如下：矿床矿化分为明显的两期,即早期和晚期,分别对应类型1和类型2两种热液流体.早期流体具相对高的W¹⁸O值（-5.3‰~-4.7‰）,温度不低于260℃;晚期流体W¹⁸O值相对偏低（-9.3‰~-6.0‰）,温度250℃以上.类型1流体发生深部循环,淋滤Ca和M n元素,在早期矿化过程中形成钙菱镁矿、钙锰辉石.与浅成水混合的类型2流体沿新通道上升,富含Au、Ag元素.在晚期矿化过程中,流体上升至沸腾带（ < 850 m）,金、银在250℃沉淀成矿.     

新疆鄯善碱泉子—巴里坤洛包泉活动断裂带研究

通过对碱泉子—洛包泉活动断裂带中碱泉子、红山口及洛包泉3 条活断层断坎微地貌的实测,尤其是对洛包泉活断层地衣直径及醉汉林胸径的实测,认为碱泉子活断层中全新世以来的垂直活动速率为0.99±0.02 m m /a～1.85±0.03 m m /a;红山口左旋正断层构成顺坡向断层陡坎,坎高1.6～7.0 m ,中全新世以来垂直活动速率为0.26±0.02 m m /a～0.95±0.06 m m /a,按其形成的水系左错1.6～2.8 m 计算,其水平活动速率为0.22±0.01 m m /a～0.38±0.03 m m /a,红山口活断层滑动速率为0.35～1.02 m m /a;洛包泉活断层地表破裂带长13 km ,断坎高3.6～14.8 m ,是由1914 年8 月5 日发生的7 12 级地震造成的。     

GAME-TIBET青藏高原云和降水综合观测概况及初步结果

对中日合作青藏高原能量水分循环试验项目中云和降水的多普勒雷达观测使用的气象观测仪器和获取的资料等情况进行了总结,并给出了那曲地区水的日变化,不同 雨量计测量降水的对比分析,风速对测量降水影响,多普勒雷达资料的个例分析及云的数值模拟的等初步结果。     

Seasonal variations in coastal debris on Awaji Island, Japan

The subject of our study was Awaji Island, an island located in the west of Japan that is surrounded by sea and that has serious problems relating to coastal debris. We conducted a long-term investigation focusing on three beaches and evaluated the results. The study was designed to develop an understanding of the actual situation, to inform local citizens, and raise their concerns about the problem of debris with a view to taking action against it. We obtained the following results: the amount, type, and ratio of debris changed according to weather and ocean conditions; debris also differs according to geographical conditions; social and economic activities of the surrounding area influence the type of debris encountered. Following this study, we have continued our investigation, and are continuing to gather data. At the same time, it is important to spread our ideas and enlighten people so as to encourage them not to dump debris. We hope that these actions manage to raise the level of consciousness among local citizens and to expand their anti-debris activities.