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211.
Preferred orientation of the dominant phyllosilicate phase (serpentine) in the matrix of the Murchison meteorite (C2) was determined by X-ray pole figure goniometry. The basal plane (001) of the phyllosilicate shows a clear preferred orientation of an axial concentration type. The preferred orientation is very weak in comparison with the orientations of known terrestrial tectonites, and it resembles the weakest case observed in the loosely consolidated clayey sediments from the deep ocean bottom. However, gentle sedimentation of platy phyllosilicate grains on a flat surface under a weak gravity field does not generate a sufficient preferred orientation. It is suggested that the preferred orientation in the matrix of Murchison was generated by uniaxial compaction, and the magnitude of strain to give rise to the observed degree of preferred orientation is evaluated as ?9%. There are two possible explanations of the deformation: dynamic compression caused by impact, and static compaction in a parent body. Though the latter case appears to be appropriate in the present case, it is not straightforward, however, to conclude that the suggested deformation is caused by burial compaction along gravity under lithostatic stress in a small primitive parent body. 相似文献
212.
Mohd Yunus Shah Kato K. Ayemi Prakash Kumar Shrivastava 《Journal of the Geological Society of India》2017,90(3):371-377
Sea ice formation in Quilty Bay, East Antarctica shows a strong relationship with climatic conditions and its spatial variation is established by GPR survey over the sea ice during the austral winters. The study also evaluates the variability of sea ice thickness and extent with local weather parameters between 2010 and 2014. Profiling on sea ice in Quilty Bay shows that sea ice thickness decreases gradually towards east. The overall thickness of sea ice is considerably less at the centre of the bay as compared to the coastal side. Two types of fast ice layers have been delineated from GPR surveys i.e. top layer fast ice which incorporates very low density surface snow and underlying high density fast ice i.e. with melt water pockets. Development of sea ice is influenced by persistent easterly winds, temperature fluctuations and ocean currents. Sea ice reveal average annual cyclic trend in Quilty Bay with maximum development in the year 2013 (157.54 cm) and the minimum development has been observed in the year 2010 (99.04 cm).The cyclic pattern of average sea ice accumulation data show perfect inverse correlation with surface air temperature, with measure of reliability R2 = 0.93. However, moderate (R2 = 0.52) and good (R2 = 0.69) degree of inverse relationship is observed with surface snow and overall sea ice (snow and ice) respectively. With 0.46 °C change in temperature, there is 33% change in sea ice condition in Quilty Bay which may remain same as far as ice extents in the region. Besides this easterly winds play a vital role in controlling the snow/ice distribution patterns as reflected by isopach maps. 相似文献
213.
Depositional Age of a Fossil Whale Bone from São Paulo Ridge,South Atlantic Ocean,Based on Os Isotope Stratigraphy of a Ferromanganese Crust
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Tatsuo Nozaki Yutaro Takaya Takashi Toyofuku Ayaka Tokumaru Kosuke T. Goto Qing Chang Jun‐ichi Kimura Yasuhiro Kato Katsuhiko Suzuki Adolpho Herbert Augustin Hiroshi Kitazato 《Resource Geology》2017,67(4):442-450
Whale carcasses (whale falls) deposited on the deep seafloor are associated with a distinctive biotic community. A fossil whale bone recovered from São Paulo Ridge, South Atlantic Ocean, during cruise YK13–04 Leg 1 of R/V Yokosuka was covered by a ferromanganese (Fe–Mn) crust approximately 9 mm thick. Here, we report an age constraint for this fossil bone on the basis of Os isotopic stratigraphy (187Os/188Os ratio) of the Fe–Mn crust. Major‐ and trace‐element compositions of the crust are similar to those of Fe–Mn crusts of predominantly hydrogenous origin. Rare earth element concentrations in samples of the crust, normalized with respect to Post‐Archean average Australian Shale, exhibit flat patterns with positive Ce and negative Y anomalies. These results indicate that the Fe–Mn crust consists predominantly of hydrogenous components and that it preserves the Os isotope composition of seawater at the time of its deposition. 187Os/188Os ratios of three Fe–Mn crust samples increased from 0.904 to 1.068 in ascending stratigraphic order. The value of 1.068 from the surface slice (0–3 mm depth in the crust) was identical to that of present‐day seawater within error (~1.06). The value of 0.904 from the basal slice (6–9 mm) equaled seawater values from ca. 4–5 Ma. Because it is unknown how long the bone lay on the seafloor before the Fe–Mn crust was deposited, the Os stratigraphic age of ca. 5 Ma is a minimum age of the fossil. This is the first application, to our knowledge, of marine Os isotope stratigraphy for determining the age of a fossil whale bone. Such data may offer valuable insights into the evolution of the whale‐fall biotic community. 相似文献
214.
T. Kato 《Meteorology and Atmospheric Physics》1997,63(1-2):39-51
Summary Quantitatively comparative experiments of moist convection using hydrostatic and non-hydrostatic models are reviewed and a further study is made of the suitability of the hydrostatic approximation for a high-resolution model when the grid size falls below 20 km. Idealized moist convection is treated, and then the torrential rain that occurred on 6 August 1993 in Kagoshima, southern Kyushu, Japan is simulated by each model. An explicit warm-rain process predicting cloud water and rainwater and the scheme of moist convective adjustment are individually or conjunctively employed in the model. The effect of hydrostatic water loading is also examined in detall.For the simulation of idealized convection, the hydrostatic simulation tends to overestimate and overexpand precipitation in comparison with the non-hydrostatic counterpart, and the drag effect of hydrostatic water loading is more significant for convective development than the non-hydrostatic effect. In the 20-km simulations, however, the hydrostatic simulation with hydrostatic water loading produces results that are comparable to the nonhydrostatic counterpart. For the simulation with real data, the comparative results well correspond to those of idealized convection. Furthermore, the 5 km hydrostatic simulation overestimates total precipitation more than that of dealized convection. On the basis of these results, when developing 1020 km numerical weather prediction (NWP) models, hydrostatic water loading should be evaluated in preference to adopting non-hydrostatic models, and a non-hydrostatic model with hydrostatic water loading is thought to be recommendable for a high-resolution NWP model.With 7 Figures 相似文献
215.
Geochemical constraints on the origin of bimodal magmatism at the Okinawa Trough, an incipient back-arc basin 总被引:23,自引:0,他引:23
The magmatism at the axial zone of the middle Okinawa Trough, a young continental back-arc basin, comprises a bimodal basaltic–rhyolitic suite, accompanied by minor intermediate rocks. We report major and trace element and Sr–Nd isotopic data for the intermediate to silicic suites, to provide constraints on their petrogenesis. The rhyolites, recovered as lava and pumice, fall into three geochemical groups (type 1, 2, and 3 rhyolites). Type 1 rhyolites have 87Sr/86Sr (0.7040–0.7042) and 143Nd/144Nd (0.5128–0.5129) identical to those of associated basalts, and are characterized by highly fractionated REE patterns. Petrogenesis of type 1 rhyolites is explicable in terms of fractional crystallization of the associated basalt. In contrast, type 2 rhyolites and andesite have slightly higher 87Sr/86Sr (0.7044–0.7047) but similar 143Nd/144Nd (0.5128) compared to those of the basalts. The compositions of type 2 rhyolite and andesite can be explained by assimilation and fractional crystallization (AFC) processes of the basalt magma; quantitative analysis suggests assimilation/fractional crystallization (Ma/Mc) ratios of ≤0.05. Hybrid andesite generated by mixing of evolved basalt and type 1 rhyolite is also present. We emphasize that mechanical extension in this part of the Okinawa Trough involves gabbroic lower crust that resulted from fractionation of mantle-derived basaltic magmas. Type 3 rhyolite occurs only as pumice, which makes its derivation questionable. This rhyolite has major and trace element compositions and Sr–Nd isotopic ratios, which suggests that it may be derived from volcanic activity on the southern Ryukyu volcanic front, and arrived in the Okinawa Trough by drifting on the Kuroshio Current. 相似文献
216.
217.
Deung-Lyong Cho Tae-Ho Lee Yutaka Takahashi Takenori Kato Keewook Yi Shinae Lee Albert Chang-sik Cheong 《地学前缘(英文版)》2021,(4):185-201
Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks from the Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia.Ion microprobe data for magmatic zircon domains from eight mafic to intermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean ~(206)Pb/~(238)U ages spanning the entire Permian period(302–254 Ma).Under cathodoluminescence,primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating,irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios( 0.2).These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids.Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton,together with the Yeongnam Massif in southern Korea.The arc magmatism along this system was commenced in the Carboniferous and culminated in the Permian–Triassic transition period.Highly positive εHf(t) values( +12) of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism.On the other hand,near-chondritic εHf(t) values(+5 to-2) of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin.Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints.Resumed highly positive zircon εHf(t) values(+9) shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust. 相似文献