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121.
Shogo Aoki Chiho Kabashima Yasuhiro Kato Takafumi Hirata Tsuyoshi Komiya 《地学前缘(英文版)》2018,9(4):1049-1072
Banded Iron Formations(BIFs) are chemical sediments, ubiquitously distributed in the Precambrian supracrustal belts; thus their trace element compositions are helpful for deciphering geochemical evolution on the Earth through time. However, it is necessary to elucidate factors controlling the whole-rock compositions in order to decode the ancient seawater compositions because their compositions are highly variable. We analyzed major and trace element contents of the BIFs in the 3.8-3.7 Ga Isua supracrustal belt(ISB), southern West Greenland. The BIFs are petrographically classified into four types:Black-,Gray-, Green-and White-types, respectively. The Green-type BIFs contain more amphiboles, and are significantly enriched in Co, Ni, Cu, Zn, Y, heavy rare earth element(HREE) and U contents. However,their bulk compositions are not suitable for estimate of seawater composition because the enrichment was caused by secondary mobility of metamorphic Mg, Ca and Si-rich fluid, involvement of carbonate minerals and silicate minerals of olivine and pyroxene and/or later silicification or contamination of volcanic and clastic materials. The White-type BIFs are predominant in quartz, and have lower transition element and REE contents. The Gray-type BIFs contain both quartz and magnetite. The Black-type BIFs are dominated by magnetite, and contain moderate to high transition element and REE contents. But,positive correlations of V, Ni, Zn and U contents with Zr contents suggest that involvement of detrital,volcanic and exhalative materials influences on their contents. The evidence for significant influence of the materials on the transition element contents such as Ni in the BIFs indicates the transition element contents in the Archean ocean were much lower than previously estimated. We reconstructed secular variations of V,Co, Zn and U contents of BIFs through time, which show Ni and Co contents decreased whereas V, Zn and U contents increased through time. Especially, the Ni and Co contents drastically decreased in the Mesoarchean rather than around the Great Oxidation Event. On the other hand, the V,Zn and U contents progressively increased from the Mesoarchean to the Proterozoic. Stratigraphical trends of the BIFs show increase in Y/Ho ratios and decrease in positive Eu anomaly upwards, respectively. The stratigraphic changes indicate that a ratio of hydrothermal fluid to seawater component gradually decrease through the deposition, and support the Eoarchean plate tectonics, analogous to the their stratigraphic variations of seafloor metalliferous sediments at present and in the Mesoarchean. 相似文献
122.
Tsuyoshi Iizuka Malcolm T. McCulloch Tsuyoshi Komiya Takazo Shibuya Kenji Ohta Haruka Ozawa Emiko Sugimura Kenneth D. Collerson 《Contributions to Mineralogy and Petrology》2010,160(6):803-823
Mt. Narryer and Jack Hills meta-sedimentary rocks in the Narryer Gneiss Complex of the Yilgarn Craton, Western Australia are
of particular importance because they yield Hadean detrital zircons. To better understand the tectonothermal history and provenance
of these ancient sediments, we have integrated backscattered scanning electron images, in situ U–Pb isotopic and geochemical
data for monazites from the meta-sediments. The data indicate multiple periods of metamorphic monazite growth in the Mt. Narryer
meta-sediments during tectonothermal events, including metamorphism at ~3.3–3.2 and 2.7–2.6 Ga. These results set a new minimum
age of 3.2 Ga for deposition of the Mt. Narryer sediments, previously constrained between 3.28 and ~2.7 Ga. Despite the significant
metamorphic monazite growth, a relatively high proportion of detrital monazite survives in a Fe- and Mn-rich sample. This
is likely because the high Fe and Mn bulk composition resulted in the efficient shielding of early formed monazite by garnet.
In the Jack Hills meta-sediments, metamorphic monazite growth was minor, suggesting the absence of high-grade metamorphism
in the sequence. The detrital monazites provide evidence for the derivation of Mt. Narryer sediments from ca. 3.6 and 3.3 Ga
granites, likely corresponding to Meeberrie and Dugel granitic gneisses in the Narryer Gneiss Complex. No monazites older
than 3.65 Ga have been identified, implying either that the source rocks of >3.65 Ga detrital zircons in the sediments contained
little monazite, or that >3.65 Ga detrital minerals had experienced significant metamorphic events or prolonged sedimentary
recycling, resulting in the complete dissolution or recrystallization of monazite. 相似文献
123.
Seitaro Urakawa Shin-ichiro Okumura Tsuyoshi Sakamoto Shinsuke Abe Kohei Kitazato Sunao Hasegawa Nobuyuki Kawai Shogo Nagayama Michitoshi Yoshida 《Icarus》2011,215(1):17-26
We present lightcurve observations and multiband photometry for 107P/Wilson-Harrington using five small- and medium-sized telescopes. The lightcurve has shown a periodicity of 0.2979 day (7.15 h) and 0.0993 day (2.38 h), which has a commensurability of 3:1. The physical properties of the lightcurve indicate two models: (1) 107P/Wilson-Harrington is a tumbling object with a sidereal rotation period of 0.2979 day and a precession period of 0.0993 day. The shape has a long axis mode (LAM) of L1:L2:L3 = 1.0:1.0:1.6. The direction of the total rotational angular momentum is around λ = 310°, β = −10°, or λ = 132°, β = −17°. The nutation angle is approximately constant at 65°. (2) 107P/Wilson-Harrington is not a tumbler. The sidereal rotation period is 0.2979 day. The shape is nearly spherical but slightly hexagonal with a short axis mode (SAM) of L1:L2:L3 = 1.5:1.5:1.0. The pole orientation is around λ = 330°, β = −27°. In addition, the model includes the possibility of binary hosting. For both models, the sense of rotation is retrograde. Furthermore, multiband photometry indicates that the taxonomy class of 107P/Wilson-Harrington is C-type. No clear rotational color variations are confirmed on the surface. 相似文献
124.
Summary. The motion of a layered seabed induced by propagating gravity water waves is modelled by the coupling matrix for a massless incompressible elastic bed according to Yamamoto. An amplitude inversion scheme is developed to extract the bottom shear modulus profile from the motion of the seabed at a point on the bed surface using the linear inverse theory combined with the Yamamoto theory of wave-seabed interaction. Numerical tests using synthetic data without noise confirmed that the inversion is unique and consistent. The inversion technique is applied to a set of field data from the Mississippi River Delta. A good agreement is obtained between the inverted profile and the direct measurements. 相似文献
125.
Yuichiro Ueno Hisayoshi YurimotoHideyoshi Yoshioka Tsuyoshi KomiyaShigenori Maruyama 《Geochimica et cosmochimica acta》2002,66(7):1257-1268
In-situ ion microprobe measurements of carbon isotopic compositions of graphite were made in seven metasediments and two carbonate rocks from the ca. 3.8 Ga Isua supracrustal belt, West Greenland. The δ13C values of micron-scale graphite globules in the metasediments and the carbonate rocks vary from -18 to +2‰ and from -7 to -3‰, respectively. The maximum δ13C value of graphite globules in the metasediment rises from -14 to -5‰, as the metamorphic grade increases from epidote-amphibolite to upper amphibolite facies. In a single hand specimen, the δ13C values of graphite inclusions in garnet are ∼7‰ lower on average than those outside garnet. Similarly, graphite armored by quartz apparently shows a few permil lower δ13C values than those on grain boundaries between noncarbonate minerals. The fact that early crystallized minerals include relatively 13C-depleted graphite indicates that the regional metamorphism increased the δ13C values of the Isua graphite. This is consistent with the regional trend of 13C-enrichment accompanied by the increase of metamorphic grade. The minimum fractionation between graphite and carbonate is consistent with the equilibrium fractionation at about 400 to 550 °C. These observations indicate that isotopic exchange with isotopically heavy carbonate caused 13C-enrichment of Isua graphite. The δ13C values of graphite reported here (δ13C > -18‰) were produced either as a metamorphic modification of organic carbon with initially much lower δ13C values, or as an abiological reaction such as decomposition of carbonate. If the isotopic exchange between carbonate and graphite during regional metamorphism controlled the 13C-enrichment of Isua graphite, previously reported large 13C-depletion of graphite, especially armored by apatite (Mojzsis et al., 1996) was probably premetamorphic in origin. This supports the existence of life at Isua time (ca. 3.8 Ga). 相似文献
126.
Seasonality of the Interaction between Convection over the Western Pacific and General Circulation in the Northern Hemisphere 总被引:2,自引:0,他引:2
The seasonality of the interaction between convection over the western Pacific and general circulation in the Northern Hemisphere (NH) is analyzed in the present paper with singular value decomposition (SVD) and empirical orthogonal function (EOF) analysis approaches, based on 500 hPa monthly mean geopotential height data and high-cloud amount data. The analyses demonstrate that coupled dominant patterns in the interaction between the convection over the western Pacific and the general circulation in NH are different in various seasons. In spring, the convection over the western Pacific is closely related with the western Atlantic (WA) and North Pacific (NP) like patterns of the general circulation in NH, and some associations between the WA and NP like pat?terns and the El Ni?o / Southern Oscillation (ENSO) cycle are also existed. The Pacific Japan (PJ) pattern is the dom?inant pattern in the interaction between the interannual variabilities of the convection over the western Pacific and the general circulation in NH summer. The WA like pattern and 3-4 year period oscillation are also relatively obvious for the summer case. In autumn, the convection over the western Pacific is closely linked with the Eurasian (EU) like pattern and the Atlantic oscillation in the general circulation in NH, it is suggested that in autumn the vitiation of convective activity over the western Pacific is largely affected by the general circulation anomaly (cold air from high latitudes) through EU like teleconnection pattern. Abrupt change happened by the end of 1980’s in the autumn interaction. The strong interaction between the western Pacific (WP) and EU like patterns in the general circulation in NH and the convection over the western Pacific and a linear trend of increasing of this interaction are also suggested in winter. It is also demonstrated that the interaction in summer and winter is stronger than in the transition seasons (spring and autumn). 相似文献
127.
128.
129.
Akira Ishiwatari Yuki Yanagida Yi‐Bing Li Teruaki Ishii Satoru Haraguchi Kazuto Koizumi Yuji Ichiyama Masaru Umeka 《Island Arc》2006,15(1):102-118
Abstract During the Hakuho‐Maru KH03‐3 cruise and the Tansei‐Maru KT04‐28 cruise, more than 1000 rock samples were dredged from several localities over the Hahajima Seamount, a northwest–southeast elongated, rectangular massif, 60 km × 30 km in size, with a flat top approximately 1100 m deep. The rocks included almost every lithology commonly observed among the on‐land ophiolite outcrops. Volcanic rocks included mid‐oceanic ridge basalt (MORB)‐like tholeiitic basalt and dolerite, calc‐alkaline basalt and andesite, boninite, high‐Mg adakitic andesite, dacite, and minor rhyolite. Gabbroic rocks included troctolite, olivine gabbro, olivine gabbronorite (with inverted pigeonite), gabbro, gabbronorite, norite, and hornblende gabbro, and showed both MORB‐type and island arc‐type mineralogies. Ultramafic rocks were mainly depleted mantle harzburgite (spinel Cr? 50–80) and its serpentinized varieties, with some cumulate dunite, wehrlite and pyroxenites. This rock assemblage suggests a supra‐subduction zone origin for the Hahajima Seamount. Compilation of the available dredge data indicated that the ultramafic rocks occur in the two northeast–southwest‐oriented belts on the seamount, where serpentinite breccia and gabbro breccia have also developed, but the other areas are free from ultramafic rocks. Although many conical serpentinite seamounts 10 km in size are aligned along the Izu–Ogasawara (Bonin)–Mariana forearc, the Hahajima Seamount may be better interpreted as a fault‐bounded, uplifted massif composed of ophiolitic thrust sheets, resembling the Izki block of the Oman ophiolite in its shape and size. The ubiquitous roundness of the dredged rocks and their thin Mn coating (<2 mm) suggest that the Hahajima Seamount was uplifted above sealevel and wave‐eroded, like the present Macquarie Is., a rare example of ophiolite exposure in an oceanic setting. The Ogasawara Plateau on the Pacific Plate is adjacent to the east of the Hahajima Seamount, and collision and subduction of the plateau may have caused uplift of the forearc ophiolite body. 相似文献
130.
Tsuyoshi Nohara Hidemi Tanaka Kunio Watanabe Noboru Furukawa Akira Takami 《Island Arc》2006,15(4):537-545
Abstract The spatial hydrogeological and structural character of the active Mozumi-Sukenobu Fault (MSF) was investigated along a survey tunnel excavated through the MSF in the Kamioka Mine, central Japan. Major groundwater conduits on both sides of the MSF are recognized. One is considered to be a subvertical conduit between the tunnel and the surface, and the other is estimated to be a major reservoir of old meteoric water alongside the MSF. Our studies indicate that part of the MSF is a sub-vertical continuous barrier that obstructs younger meteoric water observed in the south-eastern part of the Active Fault Survey Tunnel (AFST) and water recharge to the rock mass intersected by the north-western part of the AFST. The MSF might be a continuous barrier resulting in the storage of a large quantity of older groundwater to the northwest. The observations and results of in situ hydraulic tests indicate that the major reservoir is not the fault breccia associated with the northeast–southwest trending faults of the MSF, but the zone in which blocks of fractured rocks occur beside high angle faults corresponding to X shears whose tectonic stress field coincides with the present regional stress field and antithetic Riedel shears of the MSF. The results from borehole investigations in the AFST indicate that secondary porosity is developed in the major reservoir due to the destruction of filling minerals and fracture development beside these shears. The increase in hydraulic conductivity is not directly related to increased density of fractures around the MSF. Development of secondary porosity could cause the increase in hydraulic conductivity around the MSF. Our results suggest that minor conduits of the fracture network are sporadically distributed in the sedimentary rocks around the MSF in the AFST. 相似文献