长江口沉积物210Pb分布及沉积环境解释   总被引：19，自引：0，他引：19  

段凌云  王张华  李茂田  潘建明  陈中原  Yishiki Saito  Yutaka kanai 《沉积学报》2005,23(3):514-522

在长江河口潮滩、分流河道和水下三角洲共获得18个柱样,进行沉积学分析和210Pb测定,并对其中6根柱样进行137Cs测定。经研究发现,长江口外在水深25～30m,122°30′N,31°00′E附近存在一个泥质沉积中心,沉积速率达2.0～6.3cm/yr。另外,在潮滩和涨潮槽也获得较高沉积速率,其中南汇和横沙岛潮滩沉积速率(1.03～1.94cm/yr)高于崇明东滩(0.51～0.76cm/yr),涨潮槽沉积速率也达0.86cm/yr。此外,在石洞口、南汇、九段沙潮滩和三角洲前缘有部分柱样未获沉积速率,推测为沉积环境不稳定或沉积速率过快所致。  相似文献   

Rare Earth, Major and Trace Elements in the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan   总被引：1，自引：0，他引：1  

Yasuhiro Kato    Koichiro Fujinaga  Tatsuo Nozaki    Kentaro Nakamura    Ryuji Ono  Hiroshi Osawa 《Resource Geology》2005,55(4):291-300

Abstract. Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today.  相似文献   

Quantitative assessment on the influence of heavy rainfall on the crystalline schist landslide by monitoring system -case study on Zentoku landslide, Japan   总被引：2，自引：1，他引：2  

Yong Hong  Hiromasa Hiura  Kazuo Shino  Kyoji Sassa  Hiroshi Fukuoka 《Landslides》2005,2(1):31-41

On Shikoku Island, which is one of the four main islands of Japan, a large number of large-scale crystalline schist landslides have been revealed and are being monitored by an observation system. Seasonal heavy rainfall is the most active meteorological factor that can threaten the stability of this kind of site-specific landslide. In this paper, on the basis of the study of the rainfall-related behavior of a typical crystalline schist landslide, the Zentoku landslide, by analyzing the precisely and continuously observed piezometric and movement data, a method was developed to quantitatively assess the effect of heavy rainfall on a large-scale landslide. The results indicated that heavy rainfall-induced landslide displacement shows good correlation with the variation of groundwater levels. Variations of groundwater level have been simulated with the use of a tank model. The simulation using this model permits the change in water levels for future rainfall events to be predicted. By combining the predicted results with the empirical relation between displacements and water levels, rainfall-induced landslide movement during extreme rainfall events can be estimated in advance. The effect of heavy rainfall on sliding behavior can be quantified in terms of the change in displacement. Thus warning information or advisories for the local residents can be provided.  相似文献   

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon     

Hiroshi Hidaka  Janusz Janeczek  Rodney C. Ewing 《Geochimica et cosmochimica acta》2005,69(3):685-694

To study geochemical processes for migration and fixation of fissiogenic rare earth elements (REE) in association with uranium dissolution, in situ isotopic analyses using an ion microprobe were performed on U- and REE-bearing secondary minerals, such as coffinite, françoisite, uraniferous goethite, and uraninite found in a sandstone layer 30 to 110 cm beneath a natural fission reactor at Bangombé, Gabon. Phosphate minerals such as phosphatian coffinite and françoisite with depleted ²³⁵U (²³⁵U/²³⁸U = 0.00609 to 0.00638) contained large amount of fissiogenic light REE, while micro-sized uraninite grains in a solid bitumen aggregate have normal U isotopic values (²³⁵U/²³⁸U = 0.00725) and small amount of fissiogenic REE components. The proportions of fissiogenic and non-fissiogenic REE components in four samples from the core of BAX03 vary in depth ranging from 30 cm to 130 cm beneath the reactor, which suggests mixing between fissiogenic isotopes from the reactor and non-fissiogenic isotopes from original minerals in the sandstone. Significant chemical fractionation was observed between Ce and the other REE in the secondary minerals, which shows evidence of an oxidizing atmosphere during their formation. Pb-isotopic analyses of individual minerals do not directly provide chronological information because of the disturbance of U-Pb decay system due to recent geologic alteration. However, systematic Pb-isotopic results from all of the minerals reveal the mobilization of fissiogenic isotopes, Pb and U from the reactor in association with dolerite dyke intrusion ∼0.798 Ga ago and the formation of the secondary minerals by mixing event between 2.05 Ga-old original minerals and reactor materials due to recent alteration.  相似文献   

U-Pb and Pb-Pb ages of zircons from basaltic eucrites: Implications for early basaltic volcanism on the eucrite parent body     

Keiji Misawa  Akira Yamaguchi  Hiroshi Kaiden 《Geochimica et cosmochimica acta》2005,69(24):5847-5861

We have undertaken petrologic and SHRIMP U-Th-Pb isotopic studies on zircons from basaltic eucrites (Yamato [Y]-75011, Y-792510, Asuka [A]-881388, A-881467 and Padvarninkai) with different thermal and shock histories. Eucritic zircons are associated with ilmenite in most cases and have subhedral shapes in unmetamorphosed and metamorphosed eucrites. Some zircons in highly metamorphosed eucrites with granulitic texture occur alone in pyroxene, and typically have rounded to subrounded shapes due to recrystallization. Superchondritic Zr/Hf ratios of eucritic zircons indicate that they crystallized from incompatible element-rich melts after crystallization of ilmenite. Concentrations of uranium and thorium in zircons in the unmetamorphosed eucrite Y-75011 are higher than those in metamorphosed eucrites.The U-Pb systems of eucritic zircons are almost concordant but some zircon grains show reverse discordance. Radiogenic lead-loss up to 48% from zircons is observed in the shock-melted eucrite Padvarninkai. The ²⁰⁷Pb-²⁰⁶Pb ages of zircon in Y-75011 (4550 ± 9 Ma, n = 5) are nearly identical, within analytical uncertainty, to the ages of zircons from the metamorphosed eucrite Y-792510 (4545 ± 15 Ma, n = 13), the highly metamorphosed eucrites A-881388 (4555 ± 54 Ma, n = 5) and A-881467 (4558 ± 13 Ma, n = 8), and the shock-melted eucrite Padvarninkai (4555 ± 13 Ma, n = 18). The averaged ²⁰⁷Pb-²⁰⁶Pb age of zircon from five eucrites analyzed in this study is 4554 ± 7 Ma (95% confidence limits, n = 49), indistinguishable from the averaged U-Pb age (4552 ± 9 Ma) of the same samples. Because of the high closure temperature of lead in zircon (T_closure = ∼1050°C with a cooling rate of 0.2°C/yr), the ²⁰⁷Pb-²⁰⁶Pb ages of eucritic zircon do not represent metamorphic ages but crystallization ages of extrusive lavas.This fact strongly suggests that volcanism of the eucrite parent body occurred at a very early stage of the Solar System history, 7-20 Ma after CAI formation (4567.2 ± 0.6 Ma), thus basaltic eucrites crystallized from parental magmas within a short interval following the differentiation of their parent body. The U-Pb ages of eucritic zircons are older than the U-Pb, Sm-Nd and Rb-Sr ages of some basaltic eucrites, which is consistent with differences in closure temperatures of each isotopic system, and suggests that thermal and shock metamorphism affected the isotopic systems of pyroxene, plagioclase and phosphates.  相似文献   

Data‐driven taxonomy matching of asteroid and meteorite     

Yuki Saito  Peng K. Hong  Takafumi Niihara  Hideaki Miyamoto  Kenji Fukumizu 《Meteoritics & planetary science》2020,55(1):193-206

The matching of asteroids and meteorites is a significant step toward a better understanding of the origin, structure, and history of the solar system. We propose a data‐driven approach for investigating common taxonomic structure between asteroids and meteorites; C‐, S‐, and V‐type for the former, and carbonaceous chondrite, ordinary chondrite, and howardite‐eucrite‐diogenite (HED) meteorite for the latter. In the numerical experiments, by checking whether the taxonomy information of meteorites improves classification for asteroid data, we examine the existence of common structure over the two domains. For this purpose, we compare the resultant accuracies of two clustering methods which are with/without the guidance of meteorite data. We observe that the guidance of meteorite taxonomy improves the accuracy for classifying asteroids, either with the reflectance spectra or major chemical compositions of meteorites. This fact serves as a piece of evidence that there is a common taxonomic structure and links between meteorites and asteroids, supporting a long‐standing hypothesis.  相似文献   

Long-term monitoring of bottom environments of the continental slope off Otsuchi Bay,northeastern Japan     

Kazumasa Oguri  Yasuo Furushima  Takashi Toyofuku  Takafumi Kasaya  Masahide Wakita  Shuichi Watanabe  Katsunori Fujikura  Hiroshi Kitazato 《Journal of Oceanography》2016,72(1):151-166

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Preface     

Makio?C.?HondaEmail author  Hiroaki?Saito  Eitarou?Oka  Toshi?Nagata 《Journal of Oceanography》2016,72(3):339-339

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Nd and Sr isotopic variations in acidic rocks formed under a peculiar tectonic environment in Miocene Southwest Japan     

Yasutaka Terakado  Hiroshi Shimizu  Akimasa Masuda 《Contributions to Mineralogy and Petrology》1988,99(1):1-10

Initial Nd and Sr isotopic ratios were obtained for middle Miocene igneous rocks as well as for related rocks from the Outer Zone of Southwest Japan to investigate the petrogenesis of acidic magmas and their relation to a peculiar tectonic environment bearing on the back-arc spreading of the Japan Sea. On the _Nd- _Sr diagram, data points for the acidic rocks fall in the – _Nd, + _Sr quadrant occupying different positions from those for sedimentary and old crustal rocks, and seem to define several subparallel lines which extend towards the lower-righthand sedimentary field. The S-type acidic rocks occupy an intermediate position between I-type rocks and sedimentary ones, a fact suggesting mixing of an igneous component and a sedimentary one. The linear mixing trend observed on the _Nd- _Sr diagram can be attained in the restricted case that the igneous component has similar Sr/Nd concentration ratios to that of the sedimentary one, which implies an intermediate to acidic composition for the igneous component. Inconsistency between the elemental and isotopic variations observed may be reconciled by considering that mixing, probably in the relatively deep part of the crust, might have occured prior to chemical differentiation processes. The episodic igneous activity and the high heat energy required to melt such materials involving sedimentary rocks may be explained by a model in which a hot mantle region probably corresponding to the rising part of the mantle convection supplied the heating energy to the Outer Zone of Southwest Japan when passing beneath Southwest Japan in the course of movement of the hot rising part from the Shikoku basin areas to the Japan Sea area.  相似文献   

Pressure and temperature dependence of cation distribution in Mg-Mn olivine     

Tadashi Akamatsu  Kiyoshi Fujino  Mineo Kumazawa  Akio Fujimura  Manabu Kato  Hiroshi Sawamoto  Takamitsu Yamanaka 《Physics and Chemistry of Minerals》1988,16(2):105-113

Synthetic (Mg_0.51, Mn_0.49)₂SiO₄ olivine samples are heat-treated at three different pressures; 0, 8 and 12 GPa, all at the same temperature (～500° C). X-ray structure analyses on these single crystals are made in order to see the pressure effect on cation distribution. The intersite distribution coefficient of Mg and Mn in M1 and M2 sites, K _D = (Mn/Mg) _M1/(Mn/Mg) _M2, of these samples are 0.192 (0 GPa), 0.246 (8 GPa) and 0.281 (12 GPa), indicating cationic disordering with pressure. The small differences of cell dimensions between these samples are determined by powder X-ray diffraction. Cell dimensions b and c decrease, whereas a increases with pressure of equilibration. Cell volume decreases with pressure as a result of a large contraction of the b cell dimension. The effect of pressure on the free energy of the cation exchange reaction is evaluated by the observed relation between the cell volume and the site occupancy numbers. The magnitude of the pressure effect on cation distribution is only a fifth of that predicted from the observed change in volume combined with thermodynamic theory. This phenomenon is attributed to nonideality in this solid solution, and nonideal parameters are required to describe cation distribution determined in the present and previous experiments. We use a five-parameter equation to specify the cationic equilibrium on the basic of thermodynamic theory. It includes one energy parameter of ideal mixing, two parameters for nonideal effects, one volume parameter, and one thermal parameter originated from the lattice vibrational energy. The present data combined with some of the existing data are used to determine the five parameters, and the cation distribution in Mg-Mn olivine is described as a function of temperature, pressure, and composition. The basic framework of describing the cationic behavior in olivine-type mineral is worked out, although the result is preliminary: each of the determined parameters is not accurate enough to enable us to make a reliable prediction.  相似文献