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71.
Lanthanide tetrad effect in bulk chondrules from two moderately altered CM chondrites, Murchison and Yamato-793321 (Y-793321), are reported for the first time. Twenty-three chondrules were petrographically characterized and analyzed for 10 rare earth elements (REE) and other trace and major elements (Ba, Sr, Rb, K, Ca, Mg and Fe) using the precise isotope dilution technique. The results indicate systematic depletion (several times) of alkali and alkaline earths compared to CV and CO chondrules. Most of the porphyritic olivine (8 PO) and olivine-pyroxene (4 POP), porphyritic and radial pyroxene (2 PP, 1 RP), and granular olivine (1 GO) chondrules show a light-REE (L-REE) depleted, heavy-REE (H-REE) smoothly fractionated pattern composed of four (upward convex) segments possessing a relatively large negative Eu anomaly (CI-normalized La/Sm, Lu/Er and Eu/Eu* ratios = 0.3-1: Eu*, normal value). On the other hand, all barred-olivine (5 BO) chondrules, a few PO and POP indicate almost a flat L-REE pattern. In addition, regardless of their textural types, nearly half of the chondrules have a variable degree of Ce and Yb anomalies, and/or L/H-REE discontinuity, which is similar to CV and CO chondrules. The observed L- and H-convex REE patterns accompanied with the negative Eu anomaly is the first known case for chondrules as well as meteoritic materials, but have been previously reported for geological samples such as sedimentary rocks, late stage igneous and metamorphic rocks, and are explained as the lanthanide tetrad effect, which plausibly results from fluid-rock interaction. We suggest that the marked REE fractionations occurred by the selective incorporation of L-, H-REEs and Eu into alteration products in the matrix during alteration processes on the CM parent body, but that the gas/solid REE fractionation characteristics established in the nebula have basically remained unchanged. We suggest that the tetrad effects observed here represent a new index of physico-chemical conditions of fluid-rock interactions prevalent on the CM parent body. 相似文献
72.
For the appropriate management and restoration of rivers, isolated vegetation is often a practical means for improving stream habitat and ecology. The effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments. The patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid‐channel along a side wall. Several configurations of the patch and submergence ratio (i.e. water depth to the height of vegetation), and two flow conditions (i.e. below and above the sediment motion threshold) were considered. For flows below the sediment motion threshold, erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch. The degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non‐dimensional flow blockage (i.e. the product of the patch density and width). In contrast, for flows above the sediment motion threshold, sediment accumulated within and around the patch due to a reduction in bed shear stress, which was strongly influenced by the flow blockage and the obstruction ratio (i.e. the ratio of patch width to channel width). The eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch. As the flow blockage increased or as the obstruction ratio decreased, the deposition rate within and behind the patch decreased. Furthermore, the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
73.
J. Nakajima Y. Koyama M. Sekido N. Kurihara T. Kondo M. Kimura N. Kawaguchi 《Experimental Astronomy》2001,11(1):57-69
We report on the detection of VLBI fringes from quasars by a new VLBI system operating at 1 Gbps (1024 Mbits-per-second). Newly developed 1024 Msps (mega sample-per-second) AD samplers and 1024 Mbps recorders were used for the observations. A correlator with external buffers was used for the 1024 Mbps correlation processing of the tapes data.Our new VLBI system enabled 1024 Mbps VLBI, and this allowed the sampling of a 512 MHz bandwidth from a radio telescope receiver. This is the highest sampling speed ever used for VLBI, and the widest bandwidth used for VLBI observation. Initial sensitivity as evaluated by SNR comparison with earlier VLBI systems produced results to matched the expanded bandwidth. In our first observations, simultaneous optical fibre linked real-time VLBI observations were made to check the validity of data and precisely detemine the clock offsets among the radio telescopes. 相似文献
74.
Takeshi Kuritani Takeyoshi Yoshida Jun-Ichi Kimura Yuka Hirahara Toshiro Takahashi 《Mineralogy and Petrology》2014,108(1):1-11
The water content of low-K tholeiitic basalt magma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi-component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78–85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85–92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with variable compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4–5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived from a primary magma solely by olivine fractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mechanisms of low-K frontal-arc basalt magmas were also examined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at >~200 MPa. 相似文献
75.
日本南海海槽俯冲增生楔前缘的构造变形特征 总被引:1,自引:0,他引:1
对增生楔不同压力—温度条件下的构造变形、流体活动、沉积特征、岩石物性和化学组成等多方面的直接观测,可以帮助分析俯冲带地震的蕴育和发生的环境与机理。通过参加IODP的日本南海海槽发震带研究项目(NanTroSEIZE)第一阶段316航次所收集到的大量第一手数据和资料,分别在4个站位上(C0004,C0006,C0007,C0008)对日本南海海槽增生楔前缘岩芯尺度上的构造变形进行了详细分析,并且讨论了岩芯尺度上的构造变形与增生楔中大尺度的非序列分支逆冲断层和前缘逆冲断层的构造变形之间的关系。发现逆冲变形不是只在大尺度的逆冲断层面上进行,而是弥散分布在主逆冲断层面、次级逆冲断层面以及断层面之间的更小的尺度上。小尺度构造的倾向与大尺度断层的倾向有较好的一致性,表明它们是在相同的应力场下所形成的。在增生楔浅部高角度的正断层比较发育,显示张性应力场特征,同时所获得的岩芯尺度上的地层倾角较大并倾向与反射地震以及区域地质分析结果非常吻合,而在深部,特别是在大尺度逆冲断层发育带附近,各种类型的断层、滑移变形带、节理等非常普遍,同时层理与劈理的产状的复杂变化更多地受控于复杂的逆冲断层带的作用。 相似文献
76.
Yu. A. Martynov A. I. Khanchuk J. -I. Kimura A. V. Rybin A. Yu. Martynov 《Petrology》2010,18(5):489-513
Newly obtained precise analytical data on trace elements and radiogenic Sr, Nd, and Pb isotopes testify to anomalous geochemical
characteristics of mafic and intermediate Quaternary lavas in Paramushir (in the north of the Kuril arc), Kunashir and Iturup
(in the south) islands, which are the largest three islands of the Kuril island arc. The high K and LREE concentrations in
the volcanic products in Paramushir Island resulted from the southward expansion of the mantle thermal anomaly of the Kamchatka
Peninsula and the involvement of melts related to the melting of oceanic sediments in magma generation. The depleted characteristics
of the mafic volcanics are explained by the relatively young tectono-magmatic events during the opening of the Kuril backarc
basin. The Kuril island-arc system developed on a heterogeneous basement. The northern islands are a continuation of the volcanic
structures of southern Kamchatka, which were formed above an isotopically depleted and hot lithospheric mantle domain of composition
close to that of the Pacific MORB type. The southern islands were produced above an isotopically enriched and cold lithospheric
domain of the Indian-Ocean MORB type, which was modified in relation to relatively young backarc tectono-magmatic processes.
Although issues related to the genesis of the transverse geochemical zoning were beyond the originally formulated scope of
our research, the homogeneous enough isotopic composition of the rear-arc lavas in the absence of any mineralogical and geochemical
lines of evidence of crustal contamination suggests an independent magmatic source. 相似文献
77.
Binyam W. Woldemichael Jun-Ichi Kimura Daniel J. Dunkley Kenichiro Tani Hiroto Ohira 《International Journal of Earth Sciences》2010,99(8):1773-1790
The reworked Pre-Neoproterozoic and juvenile Neoproterozoic terrane of the Western Ethiopian Shield (WES) consists of three
N–S trending terranes. These are the western migmatitic gneissic terrane, the central metavolcano sedimentary terrane (CVST)
and the eastern migmatitic gneissic terrane. The eastern part of the CVST mostly consists of suture-related ultramafic-metasedimentary
complexes, whereas metavolcanics predominate in the western part. Gabbroic to granitic intrusions frequently occur in the
CVST and in adjacent areas. New zircon SHRIMP U–Pb ages for two gabbros and three diorites in the Ghimbi-Nedjo region of the
WES indicate magmatic crystallization ages. Two pulses of magmatism, at 860–850 and 795–785 Ma, are documented with the former
for the first time. The tholeiitic Kemashi diorite and Bikilal-Ghimbi gabbros have oceanic affinities and yield U/Pb zircon
ages of 856.3 ± 9.8 and 846.0 ± 7.6 Ma, respectively. The calc-alkaline Gebeya Kemisa pyroxene diorite, and the Senbet Dura
hornblende diorite plus the tholeiitic Wayu Meni gabbro, which collectively have arc-back arc characteristics are indistinguishable
at ages of 794.3 ± 9.4, 787.7 ± 8.8 and 778.1 ± 6.3 Ma, respectively. Positive εNd (4.5–7.0) and low initial 87Sr/86Sr (0.7029 ± 0.0002) and a mean T
DM model age of 0.95 Ga for the Ghimbi-Nedjo region (mean T
DM model age of 0.95 Ga for the WES overall) indicate that the magmas were generated from juvenile Neoproterozoic depleted mantle
sources, with no discernable involvement of pre-Neoproterozoic continental crust. The occurrence of gabbros and diorites with
oceanic tholeiite affinities combined with the new ages suggests that the intrusions were emplaced in the earliest stages
of the rifting of Rodinia. This event in the WES led to the development of a passive margin and associated plume-type magmatism
at ~855 Ma. The two intrusive groups with differing magma chemistry and ages suggest that the earliest magmatism was tholeiitic
and associated with the passive margin system followed by continental breakup to form the Mozambique Ocean. The combination
of tholeiitic and calc-alkaline magmatism was related to arc and back-arc basin formation and later terrane accretion (~830–690 Ma). 相似文献
78.
79.
T. Noguchi M. Kimura T. Hashimoto M. Konno T. Nakamura M. E. Zolensky A. Tsuchiyama T. Matsumoto J. Matsuno R. Okazaki M. Uesugi Y. Karouji T. Yada Y. Ishibashi K. Shirai M. Abe T. Okada 《Meteoritics & planetary science》2014,49(7):1305-1314
We observed cross sectional ultra‐thin sections near the surface of 12 particles recovered from the S‐type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration–corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer‐to‐submicrometer‐sized sylvite was identified on the surface of Itokawa particle RA‐QD02‐0034. Separately, micrometer‐sized halite was also identified on the surface of Itokawa particle RA‐QD02‐0129. Detailed inspection of the sample processing procedures at the JAXA's Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S‐type asteroids than previously thought. 相似文献
80.
Ingrid Mann Melanie Köhler Hiroshi Kimura Andrzej Cechowski Tetsunori Minato 《Astronomy and Astrophysics Review》2006,13(3):159-228
Among the observed circumstellar dust envelopes a certain population, planetary debris disks, is ascribed to systems with
optically thin dust disks and low gas content. These systems contain planetesimals and possibly planets and are believed to
be systems that are most similar to our solar system in an early evolutionary stage. Planetary debris disks have been identified
in large numbers by a brightness excess in the near-infrared, mid-infrared and/or submillimetre range of their stellar spectral
energy distributions. In some cases, spatially resolved observations are possible and reveal complex spatial structures. Acting
forces and physical processes are similar to those in the solar system dust cloud, but the observational approach is obviously
quite different: overall spatial distributions for systems of different ages for the planetary debris disks, as opposed to
detailed local information in the case of the solar system. Comparison with the processes of dust formation and evolution
observed in the solar system therefore helps understand the planetary debris disks. In this paper, we review our present knowledge
of observations, acting forces, and major physical interactions of the dust in the solar system and in similar extra-solar
planetary systems. 相似文献