High-resolution imaging polarimetry of HL Tau and magnetic field structure     

P. W. Lucas  Misato Fukagawa  Motohide Tamura  A. F. Beckford  Yoichi Itoh  Koji Murakawa  Hiroshi Suto  Saeko S. Hayashi  Yumiko Oasa  Takahiro Naoi  Yoshiyuki Doi  Noboru Ebizuka  Norio Kaifu 《Monthly notices of the Royal Astronomical Society》2004,352(4):1347-1364

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Geochemical diversity in submarine HIMU basalts from Austral Islands, French Polynesia     

Takeshi Hanyu  Laure Dosso  Osamu Ishizuka  Kenichiro Tani  Barry B. Hanan  Claudia Adam  Shun’ichi Nakai  Ryoko Senda  Qing Chang  Yoshiyuki Tatsumi 《Contributions to Mineralogy and Petrology》2013,166(5):1285-1304

We present the first report of geochemical data for submarine basalts collected by a manned submersible from Rurutu, Tubuai, and Raivavae in the Austral Islands in the South Pacific, where subaerial basalts exhibit HIMU isotopic signatures with highly radiogenic Pb isotopic compositions. With the exception of one sample from Tubuai, the ⁴⁰Ar/³⁹Ar ages of the submarine basalts show no significant age gaps between the submarine and subaerial basalts, and the major element compositions are indistinguishable at each island. However, the variations in Pb, Sr, Nd, and Hf isotopic compositions in the submarine basalts are much larger than those previously reported in subaerial basalts. The submarine basalts with less-radiogenic Pb and radiogenic Nd and Hf isotopic compositions show systematically lower concentrations in highly incompatible elements than the typical HIMU basalts. These geochemical variations are best explained by a two-component mixing process in which the depleted asthenospheric mantle was entrained by the mantle plume from the HIMU reservoir during its upwelling, and the melts from the HIMU reservoir and depleted asthenospheric mantle were then mixed in various proportions. The present and compiled data demonstrate that the HIMU reservoir has a uniquely low ¹⁷⁶Hf/¹⁷⁷Hf decoupled from ¹⁴³Nd/¹⁴⁴Nd, suggesting that it was derived from an ancient subducted slab. Moreover, the Nd/Hf ratios of the HIMU basalts and curvilinear Nd–Hf isotopic mixing trend require higher Nd/Hf ratios for the melt from the HIMU reservoir than that from the depleted mantle component. Such elevated Nd/Hf ratios could reflect source enrichment by a subducted slab during reservoir formation.  相似文献   

Seismic activity beneath the Nankai trough revealed by DONET ocean-bottom observations     

Masaru Nakano  Takeshi Nakamura  Shin-ichiro Kamiya  Yoshiyuki Kaneda 《Marine Geophysical Researches》2014,35(3):271-284

We conducted a detailed investigation of seismic activity from January 2011 to February 2013 along the Nankai trough off the Kii Peninsula, central Japan, by using data obtained from the DONET ocean-bottom observation network. The hypocenters are mostly within the subducting Philippine Sea (PHS) plate, although a few are along the plate boundary or in the sedimentary wedge below the Kumano forearc basin. The seismic activity can be separated into events above and below 20 km depth, which corresponds approximately to the Moho. The hypocenter distributions are distinctly different for these groups. The seismic activity in the oceanic crust can be further separated into three clusters. Most of the seismic activity recorded in our data represents aftershocks of the 2004 off the Kii Peninsula earthquakes (M _JMA = 7.1, 7.4, and 6.5), which occurred in the PHS plate. The hypocenter distribution in the oceanic crust correlates well with the location of the Paleo-Zenisu ridge, which is formed by a chain of seamounts that is subducting beneath the forearc basin. The hypocenters in the uppermost mantle are aligned on a plane dipping to the southeast, consistent with the existence of a thrust fault cutting through the lithosphere of the oceanic plate. The focal mechanisms of the earthquakes show that the axis of compressive stress in the PHS plate is oriented N–S, almost perpendicular to the direction of plate convergence, indicating a complex tectonic regime in this region. These results suggest that intraplate shortening may be occurring in the subducting oceanic plate.  相似文献   

Interdecadal changes in the Asian winter monsoon variability and its relationship with ENSO and AO   总被引：1，自引：0，他引：1  

Kyung-Sook Yun  Ye-Won Seo  Kyung-Ja Ha  June-Yi Lee  Yoshiyuki Kajikawa 《Asia-Pacific Journal of Atmospheric Sciences》2014,50(4):531-540

Interdecadal changes in the Asian winter monsoon (AWM) variability are investigated using three surface air temperature datasets for the 55-year period of 1958–2012 from (1) the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis 1 (NCEP), (2) combined datasets from the European Centre for Medium-range Weather Forecasts (ECMWF) 40-yr reanalysis and interim data (ERA), and (3) Japanese 55-year reanalysis (JRA). Particular attention has been paid to the first four empirical orthogonal function (EOF) modes of the AWM temperature variability that together account for 64% of the total variance and have been previously identified as predictable modes. The four modes are characterized as follows: the first mode by a southern warming over the Indo-western Pacific Ocean associated with a gradually increasing basin-wide warming trend; the second mode by northern warming with the interdecadal change after the late 1980s; the third and fourth modes by north-south triple pattern, which reveal a phase shift after the late 1970s. The three reanalyses agree well with each other when producing the first three modes, but show large discrepancy in capturing both spatial and temporal characteristics of the fourth mode. It is therefore considered that the first three leading modes are more reliable than the rest higher modes. Considerable interdecadal changes are found mainly in the first two modes. While the first mode shows gradually decreasing variance, the second mode exhibits larger interannual variance during the recent decade. In addition, after the late 1970s, the first mode has a weakening relationship with the El Niño-Southern Oscillation (ENSO) whereas the second mode has strengthening association with the Artic Oscillation (AO). This indicates an increasing role of AO but decreasing role of ENSO on the AWM variability. A better understanding of the interdecadal change in the dominant modes would contribute toward advancing in seasonal prediction and the predictability of the AWM variability.  相似文献   

Remobilization of granitoid rocks through mafic recharge: evidence from basalt-trachyte mingling and hybridization in the Manori–Gorai area,Mumbai, Deccan Traps     

Georg F. Zellmer  Hetu C. Sheth  Yoshiyuki Iizuka  Yi-Jen Lai 《Bulletin of Volcanology》2012,74(1):47-66

Products of contrasting mingled magmas are widespread in volcanoes and intrusions. Subvolcanic trachyte intrusions hosting mafic enclaves crop out in the Manori–Gorai area of Mumbai in the Deccan Traps. The petrogenetic processes that produced these rocks are investigated here with field data, petrography, mineral chemistry, and whole rock major, trace, and Pb isotope chemistry. Local hybridization has occurred and has produced intermediate rocks such as a trachyandesitic dyke. Feldspar crystals have complex textures and an unusually wide range in chemical composition. Crystals from the trachytes cover the alkali feldspar compositional range and include plagioclase crystals with anorthite contents up to An₄₇. Crystals from the mafic enclaves are dominated by plagioclase An_72–90, but contain inclusions of orthoclase and other feldspars covering the entire compositional range sampled in the trachytes. Feldspars from the hybridized trachyandesitic dyke yield mineral compositions of An_80–86, An_47–54, Ab_94–99, Or_45–60, and Or_96–98, all sampled within individual phenocrysts. We show that these compositional features are consistent with partial melting of granitoid rocks by influx of mafic magmas, followed by magma mixing and hybridization of the partial melts with the mafic melts, which broadly explains the observed bulk rock major and trace element variations. However, heterogeneities in Pb isotopic compositions of trachytes are observed on the scale of individual outcrops, likely reflecting initial variations in the isotopic compositions of the involved source rocks. The combined data point to one or more shallow-level trachytic magma chambers disturbed by multiple injections of trachytic, porphyritic alkali basaltic, and variably hybridized magmas.  相似文献   

Uptake and biological effects of synthetic glucocorticoids in common carp (Cyprinus carpio)     

Kei Nakayama  Yoshiyuki Inoue  Naomi Ikeda  Naoki Hashizume  Hidekazu Murakami  Takeshi Ishibashi  Hirofumi Ikeda  Tomohiko Isobe  Shin-Ichi Kitamura  Go Suzuki 《Marine pollution bulletin》2014

Uptake and biological effects of synthetic glucocorticoids (GCs) were analyzed using common carp (Cyprinus carpio). Fish were exposed to clobetasol propionate (CP) or clobetasone butyrate (CB) individually or in mixture at 1 μg L⁻¹ for 21 days. Bioconcentration factor (BCF) of CB was calculated as 100, and BCF of CP was less than 16. No effects were found in fish erythrocyte and leukocyte numbers and serum glucose levels after exposure to the selected GCs. On the other hand, serum concentrations of free amino acids significantly increased in GC-exposed groups. Thus, exposures to synthetic GCs at relatively low concentrations seemed to cause enhancement of protein degradation and subsequent increase of serum free amino acids without a corresponding increase in serum glucose levels, an effect which might be related to partial induction of gluconeogenesis by GC.  相似文献   

Laboratory measurements of ‘porosity‐free’ intrinsic Vp and Vs in an olivine gabbro of the Oman ophiolite: Implication for interpretation of the seismic structure of lower oceanic crust          下载免费PDF全文

Satoshi Saito  Masahiro Ishikawa  Makoto Arima  Yoshiyuki Tatsumi 《Island Arc》2015,24(2):131-144

In order to determine ‘porosity‐free’ intrinsic ultrasonic compressional (Vp) and shear wave (Vs) velocities and Vp/Vs of an olivine gabbro from the Oman ophiolite, we developed a new experimental system using a piston‐cylinder type high‐pressure apparatus. The new system allowed us to measure velocities at pressures ranging from 0.20 to 1.00 GPa and at temperatures up to 300°C for Vp and 400°C for Vs. At room temperature, the Vp and Vp/Vs increase rapidly with pressure up to 0.40 GPa, while between 0.45 and 1.00 GPa the increase is more gradual. The change in increasing rate is attributed to closure of porosity at pressures above 0.45 GPa. Based on the linear regression of data obtained at higher pressures (0.45–1.00 GPa) and extrapolation to the lower pressures, combined with temperature derivatives of velocities of the sample measured at 1.00 GPa, we determined the intrinsic Vp and Vs of the sample as a function of pressure (P, in GPa) and temperature (T, in °C). The intrinsic velocities can be expressed as Vp (km/s) = 7.004 + 0.096 × P ? 0.00015 × T, and Vs (km/s) = 3.827 + 0.007 × P ? 0.00008 × T. We evaluated the intrinsic Vp and Vs of the olivine gabbro at oceanic crustal conditions and compared them with a velocity depth‐profile of the borehole seismic observatory WP‐2 area in the northwestern Pacific Basin. Although the intrinsic Vp (～7.0 km/s) and Vs (～3.8 km/s) for the olivine gabbro studied are comparable to those of seismic layer 3 in the WP‐2 area, the estimated vertical gradients of intrinsic velocities are significantly smaller than those reported from layer 3. These results suggest that velocity profiles of layer 3 in the WP‐2 area may reflect the presence of a minor porosity in lower oceanic crust, which closes with increasing depth and/or continuous changes in mineralogy of layer 3 rocks.  相似文献   

The mantle origins of Karoo picrites     

R.J. Sweeney  T.J. Falloon  D.H. Green  Y. Tatsumi   《Earth and Planetary Science Letters》1991,107(2)

Karoo picrites are divided into a volumetrically dominant high Ti-Zr (HTZ) group and a less abundant low Ti-Zr (LTZ) group. Distinguished in this way, it is then possible to use the comparison of major element compositions with those of experimentally determined partial melts of mantle peridotites to constrain the depth of segregation for each magma type. This approach also identifies the nature of source and residual mantle materials from which such magma segregation may have occurred. The LTZ group show uniformly shallow pressures (ca. 13–15 kb) of magma segregation and the HTZ group show a range of pressures (10 kb to > 30 kb) of segregation. In the HTZ group a range of K₂O, TiO₂ and Zr contents is observed, with greater concentrations in picrites which have segregated at higher pressures (high-NaK# HTZ picrites) relative to a low-NaK# HTZ picrite group (NaK#=[Na/₂O+K₂O][Na₂O+K₂O+CaO]). If we measure the refractory character of a mantle source peridotite by its CaO and Al₂O₃ content then it is shown that the LTZ picrites have segregated from sources which are more refractory than MORB or OIB sources and which lack the strong K, Ti and Zr enrichments of HTZ sources. Mixing of at least two mantle components is required to fully explain the major element and isotopic data in the HTZ group and is combined with variations in composition produced by different depths of magma segregation. Consideration of the major element phase relations coupled with trace element abundances and isotope data leads us to suggest that one component is the Kaapvaal lithospheric mantle (incompatible element enriched but relatively refractory with respect to basaltic components) and the other is asthenospheric mantle. This lithospheric mantle component is most evident in the high-NaK# HTZ picrite end-member which has segregated at a greater depth (ca. 18–32 kb). The asthenospheric component is most closely represented by the low-NaK# HTZ picrites which have segregated at pressures of 10–22 kb. The LTZ source, more refractory mantle than MORB, is inferred to be the shallow sub-continental lithospheric mantle which may also be the source of the low-MgO tholeiites related to these picrites, and therefore the source for the main phase of Karoo basaltic eruptions.  相似文献   

Existence of andesitic primary magma: An example from southwest Japan     

Yoshiyuki Tatsumi  Kyoichi Ishizaka 《Earth and Planetary Science Letters》1981,53(1):124-130

A high-magnesian andesite (SiO₂ 58.50%, MgO 9.47%) occurs at Teraga-Ike in southwest Japan. It belongs to the Setouchi volcanic rocks of middle Miocene age and carries olivine and bronzite as phenocrysts (4.2 and 1.4 modal percent, respectively). This andesite is characterized by Mg-values as high as 75, suggesting that it may be a primary andesite. Olivine phenocrysts (Fo_87–91) are in equilibrium with the groundmass (= liquid) on the basis of Fe-Mg exchange partitioning between olivine and liquid, and they have high NiO contents (up to 0.45%). Chromite inclusions in olivine and rarely bronzite have high Cr₂O₃ contents (max. 54.87%). These features strongly suggest that the Teraga-Ike andesite keeps the chemical composition of the primary magma generated in the upper mantle, and therefore verify the existence of primary andesite magmas.  相似文献   

²²⁶Ra, ²¹⁰Pb and ²¹⁰Po disequilibria in the Western North Pacific     

Yoshiyuki Nozaki  Shizuo Tsunogai 《Earth and Planetary Science Letters》1976,32(2):313-321

²²⁶Ra,²¹⁰Pb and²¹⁰Po were measured in oceanic profiles at two stations near the Bonin and Kurile trenches.²¹⁰Po is depleted by 50% on average relative to²¹⁰Pb in the surface water. In the deep water,²¹⁰Pb is about 25% deficient relative to²²⁶Ra. Based on the deficiency,²¹⁰Pb residence time with respect to removal by particulate matter was estimated to be less than 96 years in the deep water.²¹⁰Pb deficiency in the bottom water was significantly greater than that of the adjacent deep water, indicating more effective removal near or at the bottom interface.²¹⁰Pb,²¹⁰Po and Th appear to have similar overall rate constants of particulate removal throughout the water column.  相似文献