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81.
Jens M. Turowski Niels Hovius Hsieh Meng‐Long Dimitri Lague Chen Men‐Chiang 《地球表面变化过程与地形》2008,33(3):353-363
Lateral erosion in bedrock rivers is an important control on the shape of channel cross‐sections, and the coupling of channels and hillslopes. Recent observations link lateral erosion to the variability of flow. We propose two mechanisms to explain this. One is based on changing shear stress distributions within the channel with varying flood level, the other on the competition between cover and tool effects in fluvial bedrock erosion. We assess these processes for the Liwu River, Taiwan, and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
82.
The Xiaoxinancha Au-rich copper deposit is one of important Au-Cu deposits along the continental margin in Eastern China. The deposit consists of two sections: the Beishan mine (North), composed of altered rocks with veinlet-dissemination sulfides and melnicovite-dominated sulfide-quartz veins, and the Nanshan mine (South), composed of pyrrhotite-dominated sulfide-quartz veins and pure sulfide veins. The isotope compositions of noble gases extracted from fluid inclusions in ore minerals, i.e. ratios of 3He/4He, 20Ne/22Ne and40Ar/36Ar are in the ranges of 4.45―0.08 Ra, 10.2―8.8 and 306―430, respectively. Fluid inclusions in minerals from the Nanshan mine have higher 3He/4He and 20Ne/22Ne ratios whereas those from the Beishan mine have lower 3He/4He ratios. The analysis of origin, and evolution of the ore fluids and its relations with the ore-forming stages and the ages of mineralization suggests that the initial hydrothermal fluids probably come from the melts generated by partial melting of oceanic crust with the participation of fluids from the mantle (mantle-plume type)/aesthenosphere. This also corresponds to the continental margin settings during the subduction of Izanagi ocaneic plate towards the palaeo-Asian continent (123―102 Ma). The veinlet-dissemination ore bodies of the Beishan mine were formed through replacement and crystallization of the mixed fluids generated by mixing of the ascending high-temperature boiling fluid with young crustal fluid whereas the melnicovite-dominated sulfide-quartz veins were formed subsequently by filling of the high-temperature ore fluid in fissures. Pyrrhotite-dominated sulfide-quartz veins in the Nanshan mine were formed by filling-deposition-crystallization of the moderate-temperature ore fluids and the pure sulfide veins were formed later by filling-deposition-crystallization of ore substance-rich fluids after boiling of the moderate-temperature ore fluids. The metallogenic dynamic processes can be summarized as: (1) formation of fluidand ore substance-bearing Adakitic magma by degassing, dewatering and partial melting during subduction of the Izanagi plate; (2) separation and formation of ore fluids from the Adakitic magma; and (3) success-sive ascending of the ore fluids and final formation of the Au-rich Cu deposit of veinlet-dissemination and vein types by secondary boiling. 相似文献
83.
84.
The effect of sea-ice on various aspects of the Southern Hemisphere (SH) extratropical climate is examined. Two simulations using the LMD GCM are performed: a control run with the observed sea-ice distribution and an anomaly run in which all SH sea-ice is replaced by open ocean. When sea-ice is removed, the mean sea level pressure displays anomalies predominantly negatives near the Antarctic coast. In general, the meridional temperature gradient is reduced over most of the Southern Ocean, the polar jet is weaker and the sea level pressure rises equatorward of the control ice edge. The high frequency filtered standard deviation of both the sea level pressure and the 300-hPa geopotential height decreases over the southern Pacific and southwestern Atlantic oceans, especially to the north of the ice edge (as prescribed in the control). In contrast, over the Indian Ocean the perturbed simulation exhibits less variability equatorward of about 50°S and increased variability to the south. The zonal averages of the zonal and eddy potential and kinetic energies were evaluated. The effect of removing sea-ice is to diminish the available potential energy of the mean zonal flow, the available potential energy of the perturbations, the kinetic energy of the growing disturbances and the kinetic energy of the mean zonal flow over most of the Southern Ocean. The zonally averaged intensity of the subpolar trough and the rate of the baroclinic energy conversions are also weaker. 相似文献
85.
柴达木盆地北缘沉积凝灰质岩层段的地层时代 总被引:2,自引:0,他引:2
柴达木盆地北缘深部沉积凝灰质岩层段的地层归属存在2种观点,下侏罗统和石炭系。本文通过岩石薄片、微量元素、孢粉组合以及海相化石碎片等多种资料的综合分析,认为沉积凝灰质岩层段与其上的下侏罗统之间岩性、电性出现突变的主要原因是沉积时火山事件以及晚期方解石脉充填造成的,并不能代表下伏的老地层;沉积凝灰质岩层段的海相化石碎片为搬运再沉积的结果,没有地层指示意义;孢粉组合能反映沉积凝灰质岩层段沉积的地质年代,据此确认沉积凝灰质岩层段为下侏罗统湖西山组二段。 相似文献
86.
以剪切波速为宗量的一种砂土地震液化的不确定性判别法 总被引:6,自引:0,他引:6
利用基于剪切波速的砂土液化判别法,本文提出了一种可考虑剪切波速的随机性和液化及液化危害等级的模糊性的液化和液化危害等级的判别法。作者首先讨论了当剪切波速具有随机性时液化的发生概率,进而给出了确定场地液化和危害程度的发生概率。在此基础上,结合液化和液化危害程度(等级)的模糊性,利用模糊事件的概率分析方法,提出了可同时考虑随机性和模糊性的场地液化和液化危害性的发生概率的计算方法。 相似文献
87.
88.
We present TUNIS, a double‐pass spectro‐imager built in THEMIS as a proof‐of‐concept for EST. Basic concepts and selected first results are shown. We introduce the concept of a Hadamard spectral mask as a proposition to move forward from the present implementation of a single‐wavelength per image pixel to a more general one of multiplexed spectral information that improves the temporal coherence of the spectral measurement (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
89.
Xiangchun Quan Yulai Wang Weicong Xiong Mengchang He Zhifeng Yang Chunye Lin 《Environmental Earth Sciences》2010,61(8):1725-1734
The Daliao River watershed, an important industrial base of China, has been heavily influenced by anthropogenic activities.
Microbes in sediments play an important role in recycling of organics and nutrients, and knowledge of the microbial composition
and community structure in river sediments can help us to understand the contribution of microorganisms to environmental processes
and their response to environmental perturbation. In this study, 11 surface sediment samples and 1 core sediment sample were
collected from the Daliao River water system and its estuary, and their microbial abundance and community compositions were
investigated using fluorescence in situ hybridization. Results showed that total cell numbers in surface sediments from different
locations ranged from 4.2 × 108 to 16.2 × 108 cells cm−3. Domain bacteria represented 58–82% with α-, β-, and γ-proteobacteria as the major subgroups summing up to 40%. Total cell
numbers along the core sediment profile ranged from 7.9 × 108 to 20.1 × 108 cells cm−3, with relatively higher total cell numbers in the upper (0–6 cm) and middle (21–30 cm) layers. In the core sediment, domain
bacteria represented 62–85% and archaea 1.0–11.8%. α-, β- and γ-Proteobacteria were three major phylogenetic groups of bacteria
in the core sediment also with γ-proteobacteria as the most abundant subgroup accounting for 9.8–40.8% of total cells. 相似文献
90.
C. G. Menéndez M. de Castro J.-P. Boulanger A. D’Onofrio E. Sanchez A. A. Sörensson J. Blazquez A. Elizalde D. Jacob H. Le Treut Z. X. Li M. N. Núñez N. Pessacg S. Pfeiffer M. Rojas A. Rolla P. Samuelsson S. A. Solman C. Teichmann 《Climatic change》2010,98(3-4):379-403
We investigate the performance of one stretched-grid atmospheric global model, five different regional climate models and a statistical downscaling technique in simulating 3 months (January 1971, November 1986, July 1996) characterized by anomalous climate conditions in the southern La Plata Basin. Models were driven by reanalysis (ERA-40). The analysis has emphasized on the simulation of the precipitation over land and has provided a quantification of the biases of and scatter between the different regional simulations. Most but not all dynamical models underpredict precipitation amounts in south eastern South America during the three periods. Results suggest that models have regime dependence, performing better for some conditions than others. The models’ ensemble and the statistical technique succeed in reproducing the overall observed frequency of daily precipitation for all periods. But most models tend to underestimate the frequency of dry days and overestimate the amount of light rainfall days. The number of events with strong or heavy precipitation tends to be under simulated by the models. 相似文献