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241.
Masaki Yoshida 《地学学报》2019,31(2):135-149
Three‐dimensional spherical mantle convection was simulated to predict future continental motion and investigate the driving force of continental motion. Results show that both the time required (≥300 Ma from the present) and the process for the next supercontinent formation are sensitive to the choice of critical rheological parameters for mantle dynamics, such as a viscosity contrast between the upper and lower mantles and a yield strength of the lithosphere. From all the numerical models studied herein, mantle drag force by horizontal mantle flow beneath the continents may mostly act as a resistance force for the continental motion in the process of forming a new supercontinent. The maximum absolute magnitude of the tensional and compressional stress acting at the base of the moving continents is in the order of 100 MPa, which is comparable to a typical value of the slab pull force. 相似文献
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本文研究了日本内陆及其外围海域发生大地震后的地震活动迁移现象。在所研究的6个震例中,一个共同的特点是,地震活动的迁移总是沿着地壳内的活动地质构造带发生。有时可以根据地震活动的迁移来进一步确定活动构造带的存在。把板块边缘地区的地震活动类比为沿着力学偶合平面迁移和扩散,我们可以认为,岛上的活动构造带对应着地壳块体的力学相互作用边界。地震迁移的形式可能不只一种。在我们所研究的震例中发现了以下特征:地震迁移速度约为几km/年;大地震震源区之间存在着地震空区;在每一条地震带上有一定的地震活动周期。地震迁移的一种可能机制是:由于地壳块体的相对运动,在其边界上的凹凸不平区造成了构造应力集中,这些凹凸不平区相继地发生破裂,形成了地震迁移。 相似文献
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The Adachi-Medeshima pumice deposit of the Late Pleistocene age, found in Northeast Japan, contains extremely low-K tonalite fragments, having a wide variation in SiO2 content but fairly uniform K2O content (<0.1%). The tonalites coexist with essential dacite fragments. Mineralogical properties of the tonalites are the same as those of the pumice and dacite fragments. Sr isotope ratios of the tonalite, dacite fragments and pumice also fall within a narrow range. By assuming a Rayleigh fractionation model, the concentration of incompatible trace elements in cumulus phases was calculated, and the amounts of major elements were estimated from the fractionation ratios of each mineral and the volume ratio of crystal-liquid. The estimated element abundances of the cumulus phase show a MORB normalized pattern similar to that of the natural tonalite having cumulate textures. Thus, the tonalite represents the cumulus phase precipitated from dacite magma. Equilibrium temperatures and fO2 of the tonalites, dacite fragments and pumice were estimated from coexisting magnetite-ilmenite pairs at 876°–796° C and –logfO2 = 9.8–11.9, respectively. The fO2 is among highest group yet reported. This is a case of extremely low-K tonalite which formed in the island arc system different from the oceanic environments. 相似文献
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The many lives of active galactic nuclei: cooling flows, black holes and the luminosities and colours of galaxies 总被引:2,自引:0,他引:2
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Hiroshi A. Takahashi Eiichi Konohira Tetsuya Hiyama Masayo Minami Toshio Nakamura Naohiro Yoshida 《Tellus. Series B, Chemical and physical meteorology》2002,54(2):97-109
Diurnal variation in the atmospheric CO2 concentration and the carbon isotopic composition (Δ14 C and δ13 C) was measured in a forest in an urban area on 9 February 1999. The carbon isotope approach used in the present study differentiated between the quantitative contributions from anthropogenic and biogenic CO2 sources in the urban atmosphere. The anthropogenic (fossil fuel) and biogenic (soil respiration) contributions was estimated, and they ranged from 1 to 16% and from 2 to 8% of the total atmospheric CO2 . The diurnal variation of the anthropogenic CO2 was the major cause of the total atmospheric CO2 variation, while the biogenic CO2 remained relatively constant throughout the day. Estimating the contribution of soil respired CO2 provided the mean residence time of soil respired CO2 within the forest atmosphere. 相似文献