Liquid Immiscibility of Boninite in Xiangcheng, Southwestern China, and Its implication to Genetic Relationship between Boninite and Komatiitic Basalt     

Tetusro Urabe  Takagi  Naito 《《地质学报》英文版》2001,75(1):74-93

Boninitic rocks and associated high-magnesian basalt and high-iron tholeiite in the Xiangcheng area constitute the basal horizon of the arc volcanic sequence in the Triassic Yidun Island-Arc, southwestern China. The boninite occurs as pillow, massive and ocellar lavas; the last one possesses well-developed globular structure and alternates with the former two. The boninite is characterized by the absence of phenocrysts of olivine and low-Ca pyroxenes and by low CaO/Al2O3 ratios (<0.67) and high Cr (>1000 ppm) and Ni (>250 ppm). The normalized abundance patterns (NAP) of trace elements to primitive mantle are similar to the NAP of low-Ca modern boninites and SHMB in the Archaean and Proterozoic.As a mechanism of ocellar texture, liquid immiscibility in boninite is supported by the following lines of evidence: (a) sharp contact between ocelli and matrix, (b) constant volumetric ratios of ocelli/matrix and common coalescence of ocelli in ocellar rocks, (c) identical micro-spinifex textures and mineral asse  相似文献   

Role of crystalline anisotropy energy on the acquisition of stable remanent magnetization: Inverse type of thermoremanent magnetization     

Minoru Ozima  Mituko Yama-ai  Takesi Nagata 《Pure and Applied Geophysics》1963,55(1):77-90

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Phase and group velocities and Q of mantle Love and Rayleigh waves of the first two modes and their azimuthal dependences for the 1963 Kurile Islands earthquake     

Yoshio Fukao  Minoru Kobayashi 《Physics of the Earth and Planetary Interiors》1983,32(1):4-35

Phase and group velocities and Q of mantle Love and Rayleigh waves from the 1963 Kurile Islands earthquake (M_w = 8.5) were determined over 37 great circle paths by a time variable filtering technique, in a period range 100–500 s for the fundamental modes and 100–275 s for the first higher modes. The preliminary reference Earth model (PREM) explains reasonably well the average dispersion results for the fundamental Love and Rayleigh waves. There exists a small, but significant inconsistency between the observation and the model for the first higher Love and Rayleigh waves. The Q structure of PREM is inconsistent with the observation for the fundamental Love waves, but explains other observations reasonably well. The dispersion of each mode shows a clear azimuthal dependence from which the four azimuthal windows were established. The phase and group velocity measurements for each window were, in general, shown to be mutually consistent. The azimuthal variations are largest for the first higher Rayleigh waves, indicating strong lateral heterogeneity in the structure of the low velocity zone. The first of the four windows is characterized by the largest fraction of Precambrian shields and the second window by the largest fraction of normal oceans. A comparison of these two windows may give some insight into deep lateral heterogeneity between continents and oceans. The observed phase and group velocities of the first window are systematically higher than those of the second window for the fundamental Love and Rayleigh waves at periods up to 400 s, and for the first higher Love and Rayleigh waves up to 175 s. Their differences are greatest for the first higher Rayleigh waves and least for the fundamental Rayleigh waves. Although the fundamental Rayleigh waves show the least velocity differences, their persistence up to a period of longer than 300 s is in striking contrast with some of the pure path phase velocities derived earlier for continents and oceans. A set of models for continents and oceans. PEM-C and PEM-O are not consistent with our observation. The third azimuthal window is characterized by trench-marginal seas and the fourth window by mountainous areas, typically the Asian high plateaus from northern China to the Middle East through Tibet. A comparison of these two windows gives some information about deep structural differences between subduction zones and continental collision zones, both belonging to plate convergence zones. For the fundamental and the first higher Love waves, the phase and group velocities for the third window are markedly low, whereas those for the fourth window are somewhat comparable to those for the second window. Slow Rayleigh waves are evident for two windows, with the fourth window apparently being the slowest for the fundamental Rayleigh above 200 s and for the first higher Rayleigh. For the fundamental Rayleigh waves, the third window is very slow below 200 s, but becomes progressively fast as the period increases and tends to be the fastest window around 400 s, suggesting a deep seated high velocity anomaly beneath trench-marginal seas. The dispersion characteristics of the fourth window indicate a thick high velocity lid with an extensive low velocity zone beneath it. The shield-like lithosphere, coupled with an extensive low velocity zone, may be a characteristic feature of continental collision zones. The particle motion of the fundamental Love waves was found not to be purely transverse to a great-circle connecting the epicenter to a station. The departure from the purely transverse motion is systematic among different periods, different G arrivals (G₂, G₃,…) and different stations, which may be interpreted as being due to lateral refraction.  相似文献   

A seasonal effect in diurnal variation of the atmospheric electric field on the Pacific coast of Japan     

M. Takagi  A. Iwata 《Pure and Applied Geophysics》1980,118(2):953-963

The measurement of the atmospheric electric field was carried out with a field mill at a small island in a bay on the Pacific coast of Japan. The data obtained during 80 months from 1971 to 1977 were analysed. It was found that characteristically the diurnal variation regularly alters with the seasons. Whereas the electric field in winter has the same diurnal pattern as that observed at globally representative stations, it exhibits in summer a pattern depending on the variation of the local electric conductivity. The alteration is inferred to be associated with regional atmospheric conditions surrounding the observation site.  相似文献   

Effects of a plastic deformation on the remanent magnetization of a Cu-Co alloy     

Minoru Ozima 《Earth and Planetary Science Letters》1980,47(1):121-123

Compressional plastic deformation of a Cu-Co alloy in which Co particles (submicron to a few tens of microns in diameter) were precipitated in a Cu matrix resulted in a systematic rotation of remanent magnetization (IRM atH = 1000Oe) away from the axis of compression with increasing degree of the deformation.  相似文献   

²⁴¹Pu and²⁴¹Am in sediments from coastal basins off California and Mexico     

Minoru Koide  Edward D. Goldberg  Vernon F. Hodge 《Earth and Planetary Science Letters》1980,48(2):250-256

In sediments deposited in the coastal basins off the western North American continent since the early 1960's, there is more²⁴¹Am activity than one would predict if its presence was solely due to the decay of²⁴¹Pu that was produced during the testing of weapons in 1961–1962 (taken as July 1, 1962 for calculations). This excess can be accounted for by the decay of²⁴¹Pu, if pre-1962 fallout (fallout from the pre-moratorium testing) has been continuously introduced into the recent sediments along with fallout from post-moratorium testing. This hypothesis is supported by the plutonium depth profiles which do not reflect direct fallout from the atmosphere, as characterized by two peaks corresponding to the two major weapons testing periods, but continuously increasing plutonium and americium concentrations from 1954 to 1974. Thus, the nuclides may be coming from a large reservoir that has accumulated and mixed fallout since 1952. Such a concentration gradient for all of the nuclides requires their immobilization in the sediment after deposition.  相似文献   

Marine geochronology withPb     

Minoru KoideAndrew Soutar  Edward D. Goldberg 《Earth and Planetary Science Letters》1972

The application of²¹⁰Pb dating to an inshore marine deposit off the California coast has been successful. The amounts of unsupported²¹⁰Pb annually accumulated in the Santa Barbara sediments are much greater than those from lake and glacial deposits and than the amount produced through the decay of radium in the overlying water column.  相似文献   

Dependence of the effective attachment coefficient of small ions upon the size of condensation nuclei     

Yukimasa Ikebe  Minoru Kawano 《Pure and Applied Geophysics》1970,83(1):120-130

Summary To clarify the ionization equilibrium near the ground, simultaneous measurements of the rate of ion pair production (q), the concentrations of small ions (n) and condensation nuclei (Z), and the diffusion coefficient of condensation nuclei (D) were carried out at several stations in the central area of Japan. The total rate of ion pair production (q) was estimated fromq=q(Rn)+q(Tn)+q()+q(+CR). The value ofq was estimated as 10J to 20J. The mean life () and the effective attachment coefficient () of small ions were also estimated at each station. Correlations amongn, Z, q, andD were also studied. If we take the variation ofD into consideration, the correlation was expressed by the simple formula;q=n Z. The dependence of upon size of nuclei (2r) were also measured, and was found to correlate well withD orr.  相似文献   

Study of the effect of water-soluble fractions of heavy-oil on coastal marine organisms using enclosed ecosystems,mesocosms   总被引：1，自引：0，他引：1  

Ohwada K  Nishimura M  Wada M  Nomura H  Shibata A  Okamoto K  Toyoda K  Yoshida A  Takada H  Yamada M 《Marine pollution bulletin》2003,47(1-6):78-84

Mesocosm facilities composed of 4 experimental and 2 reservoir tanks (1.5 m in diameter, 3.0 m in depth and 5 tons in capacity) made of FRP plastics, were constructed in the concrete fish rearing pond in the Fisheries Laboratory, The University of Tokyo. The water-soluble fraction of Rank A heavy residual oil was formed by mixing 500 g of the oil with 10 l of seawater, which was introduced to the 5000 l-capacity tanks. Experimental Run 4 was conducted from May 31 to June 7, 2000. Oil concentrations in the tanks were 4.5 microg/l called LOW, and 13.5 microg/l, called HIGH tank. Bacterial growth rates very quickly accelerated in the HIGH tank just after the loading of oil which corresponded with a high increase of bacterial cells in the same tank after 2 days. Later, bacterial numbers in HIGH tank rapidly decreased, corresponding with the rapid increase of heterotrophic nano-flagellates and virus numbers on the same day. Sediment traps were deployed at the bottom of the experimental tanks, and were periodically retrieved. These samples were observed both under light microscope and epi-fluorescent microscope with UV-excitation. It was observed that the main components of the vertical flux were amorphous suspended matter, mostly originating from dead phytoplankton and living diatoms. It was further observed from the pictures that vertical transport of oil emulsions were probably conducted after adsorption to amorphous suspended matter and living diatoms, and were settling in the sediment traps at the bottom of the tanks. This means that the main force which drives the soluble fraction of oil into bottom sediment would be vertical flux of such amorphous suspended particles and phytoplankton. Further incubation of the samples revealed that the oil emulsions were degraded by the activity of autochtonous bacteria in the sediment in aerobic condition.  相似文献   

Improvement of seismological earth models by using data weighting in waveform inversion     

Nozomu Takeuchi  Minoru Kobayashi 《Geophysical Journal International》2004,158(2):681-694

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