Journal of Paleolimnology - Lake sediments on the Tibetan Plateau are important natural archives for studying past climate and environment changes. A precise sediment core chronology is a... 相似文献
Rocky landslides on river banks can result in the generation of ultra-high waves, which may destroy structures on the opposite bank. Existing methods to calculate the pressure on bank slopes under the effect of impulse waves generated by landslides are, however, few and of low precision. Therefore, in this study, a three-dimensional physical model test was conducted by taking into account factors such as landslide geometry parameters and the bank slope angle. The model test section was generalized on the basis of a certain section of the Three Gorges reservoir area as a prototype, after which the wave parameters and wave pressure acting on the bank slope were measured. Subsequently, the magnitude, acting point, and distribution of the pressure of the impulse waves generated by the rocky landslide upon the bank slope were determined. The distribution curve of the impact pressure was similar to that calculated using the СНиПⅡ57-75 formula, and the experimental pulsating pressure value was close to the value calculated using the Subgrade formula. Based on the test results, a power function of the relative pulsating pressure steepness with respect to the reciprocal of the wave steepness, relative water depth, and slope ratio was proposed. The acting point of the maximum pulsating pressure was found to be located near the still water level. Finally, an empirical formula for calculating the envelope of the maximum pulsating pressure distribution curve was proposed. These formulas can serve as a theoretical basis for the prediction of impulse wave pressure generated owing to landslides on bank slopes. 相似文献
Saindak is one of the typical porphyry Cu deposits (PCDs) in the Chagai magmatic arc in Pakistan. Ore-forming porphyries at Saindak PCD are mainly composed of tonalite. Here, we use geochemistry of apatite enclosed in plagioclase phenocrysts from the ore-forming tonalite to constrain the releasing and recharging processes of S and Cl in the underlying parental magma chamber during PCD mineralization. Although apatite inclusions have homogeneous intra-grain S and Cl compositions, there is significant inter-grain S and Cl variations in apatite inclusions located from core to rim in the hosting plagioclase. Such inter-grain S and Cl variation in apatites are coupled with the core-to-rim trends of An, FeO and Mg contents of the hosting plagioclase phenocryst. It indicates that the Saindak PCD likely formed by episodic injection of primitive magmas during the growth of an underlying magma chamber, rather than by one major injection or by addition of mafic melt derived from different source region. Each primitive melt injection introduced essential ore-forming materials such as S and Cl, which were rapidly and effectively released to the coexisting fluids, causing mineralization. Once primitive melt injection stops, signaling the end of growth of underlying magma chamber, mineralization will cease quickly although the hydrothermal system can still survive for a long time. However, the later released fluids are relatively depleted in ore-forming materials, and thus have lower capability to generate mineralization. Accordingly, predominant porphyry-type mineralizations occurred during the growth rather than waning stage of a magmatic system.
The natural environment provides material essentials for human survival and development. The characteristics,processes, regional differentiation and forcing mechanisms of the elements of the natural environment(e.g. geomorphology,climate, hydrology, soil, etc.) are the main objects of research in physical geography. China has a complex natural environment and huge regional differentiation and therefore it provides outstanding reserach opportunities in physical geography. This review summarizes the most important developments and the main contributions of research in the physical geography and human living environment in China during the past 70 years. The major topics addressed are the uplift of the Tibetan Plateau and the evolution of its cryosphere, the development of fluvial systems, the acidification of the vast arid region of the Asian interior, variations in the monsoon and westerly climate systems on multiple timescales, the development of lakes and wetlands, the watershed system model, soil erosion, past human-environment interactions, biogeography, and physical geographic zonality. After briefly introducing international research developments, we review the history of research in physical geography in China, focusing on the major achievements and major academic debates, and finally we summarize the status of current research and the future prospects. We propose that in the context of the national demand for the construction of an ecological civilization, we should make full use of the research findings of physical geography, and determine the patterns and mechanisms of natural environmental processes in order to continue to promote the continued contribution of physical geography to national development strategies, and to further contribute to the theory of physical geography from a global perspective. 相似文献