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991.
992.
镁同位素地球化学研究新进展及其应用 总被引:7,自引:3,他引:4
作为一种新兴的地质示踪剂,Mg同位素正受到国际地学界日益广泛的关注。Mg同位素地球化学研究已取得了巨大的进展,近期研究工作主要包括两个方面。首先,调查了地球各主要储库和陨石的Mg同位素组成特征,结果表明陨石和地球地幔具有均一并且相似的Mg同位素组成,平均δ26Mg值分别为-0.28±0.06‰和-0.25±0.07‰;相反,上地壳和水圈的Mg同位素组成很不均一,δ26Mg值变化范围分别为-4.84‰~+0.92‰和-2.93‰~+1.13‰。其次,对一些地质和物理化学过程中Mg同位素的分馏行为进行研究,结果表明:(1)地表风化作用可以造成大的Mg同位素分馏,导致重Mg同位素残留在风化产物中而轻Mg同位素进入水圈;(2)岩浆分异过程中Mg同位素平衡分馏很小;(3)高温化学扩散和热扩散过程中Mg同位素会发生显著的动力学分馏。基于这些研究成果,Mg同位素体系已经被初步应用于示踪早期地球形成和壳内物质再循环等过程,并有望在不久的将来应用于示踪大陆地壳的化学演化和地质温度计等研究领域。 相似文献
993.
地勘单位随着地质市场的完善及自身队伍的建设,经营范围及主营业务处于不断的调整变化之中,但其固有的经济运行模式符合经济统计学中的长尾理论。以某地勘单位的实际经营数据为例,从长尾理论蕴涵的市场规律出发,分析了地勘市场的特点,指出地勘市场所具有的长尾特性:长尾项目远多于短头项目,从长期看项目分布有向尾部移动的趋势,长尾项目越来越多,短头项目越来越少。依据长尾理论与行业特点,从选择策略、产品服务策略、组织架构策略、人力资源策略、营销策略等方面构建了地勘单位的发展策略,对新形势下地勘单位的发展具有一定的参考价值。 相似文献
994.
The 3-D geometry of the seismicity in Hindu Kush–Pamir–western China region has been defined by seismic records for 1975–1999 from the National Earthquake Information Center, the U.S. Geological Survey, and over 16,000 relocated earthquakes since 1975 recorded by the Xinjiang seismic network of China. The results show that most Ms ≥ 5.0 hypocenters in the area are confined to a major intracontinental seismic shear zone (MSSZ). The MSSZ, which dips southwards in Pamir has a north-dipping counterpart in the Hindu Kush to the west; the two tectonic realms are separated by the sinistral Chaman transform fault of the India–Asia collisional zone. We demonstrate that the MSSZ constitutes the upper boundary of a south-dipping, actively subducting Pamir continental plate. Three seismic concentrations are recognized just above the Pamir MSSZ at depths between 45–65 km, 95–120 km, and 180–220 km, suggesting different structural relationships where each occurs. Results from focal mechanism solutions in all three seismological concentrations show orientations of the principal maximum stress to be nearly horizontal in an NNW–SSE direction. The south-dipping Pamir subduction slab is wedge-shaped with a wide upper top and a narrow deeper bottom; the slab has a gentle angle of dip in the upper part and steeper dips in the lower part below an elbow depth of ca. 80–120 km. Most of the deformation related to the earthquakes occurs within the hanging wall of the subducting Pamir slab. Published geologic data and repeated GPS measurements in the Pamir document a broad supra-subduction, upper crustal zone of evolving antithetic (i.e. north-dipping) back-thrusts that contribute to north-south crustal shortening and are responsible for exhumation of some ultrahigh-pressure rocks formed during earlier Tethyan plate convergence. An alternating occurrence in activity of Pamir and Chaman seismic zones indicates that there is interaction between strike-slip movement of the Chaman transform fault system and deep-subduction of the Pamir earthquake zone. Pamir subduction-related seismicity becomes shallower in depth with increasing distance east of the transform fault. Therefore, sinistral movement of the Chaman transform fault appears to be influencing continental deep-subduction in the Pamir region and may provide an explanation for the unusual south-dipping geometry of the intracontinental Pamir plate. 相似文献
995.
Youliang Chen Rafig Azzam Ming Wang Shan Xu Lequn Chang 《Environmental Earth Sciences》2011,64(1):29-36
The compressive and tensile strengths of frozen clay are important parameters for frozen wall design in artificial freezing
excavation of tunnels and foundation pits. Up to now, nobody has conducted the compressive and tensile test of frozen clays
in Shanghai area. In this paper, the unconfined compressive and tensile tests of frozen clay specimens drilled from the soil
horizons 3–5 in Shanghai area were conducted in Zwick-Z020kN High-low Temperature Materials Testing Machine and Frozen Soil
Triaxial Testing Machine, the corresponding constitutive equations were suggested; the temperature-unconfined uniaxial compressive
strength relation was discussed; the strain rate–unconfined uniaxial compressive strength and strain rate–uniaxial tensile
strength relations were studied. The relation between moisture content, dry density and unconfined uniaxial compressive strength
was analyzed, too. In addition, the uniaxial compressive elastic modulus of Shanghai frozen clays and its influence factors
were discussed. The research work of the current paper is very helpful for the design and theoretical studies of artificial
freezing excavation in soft soil areas. 相似文献
996.
To study population dynamics of marine ciliates in different artificial seawaters (ASW), the population growth dynamics of a common marine ciliate Euplotes vannus were investigated using beef extract media and rice media for five types of ASW and natural seawater (NSW). The results show that: (1) the population growth rate was in the order of NSW>Flack ASW>Nakamula ASW>Schmadz ASW>Oshima ASW>Subow ASW and was considerably higher in rice media than in beef extract media (apart from Subow ASW); (2) the maximum density of E. vannus in stationary phase in each treatment was ranked as Flack ASW>Nakamula ASW>Schmadz ASW>NSW>Oshima ASW>Subow ASW, and was again higher in rice media than in beef extract media (except for Subow ASW); (3) the exponential and stationary phases were longer in rice media than in beef extract media; (4) strains of E. vannus that had been domesticated for >1 year in ASW grew significantly slower, with lower maximum density and longer stationary phase than those isolated and maintained in NSW. It was demonstrated that: (1) E. vannus may grow well in Flack, Nakamula and Schmads ASW compared with NSW (mainly in terms of growth rate); and (2) Oshima ASW is the preferred choice for stock cultures of E. vannus, but the ASWs Flack, Nakamula and Schmadz are preferred for mass culture. These findings suggest that these three ASWs are effective for the cultivation of marine protozoa for experimental studies on ecology, toxicology and molecular biology. 相似文献
997.
选取栉孔扇贝Chlamys farreri担轮幼虫为材料,采用秋水仙素-低渗-空气干燥法制备染色体标本,应用荧光显带技术,分析了DAPI带和PI带在栉孔扇贝染色体上的分布。DAPI带型结果显示,栉孔扇贝所有染色体上都存在DAPI阳性带,主要分布于传统的着丝粒区和端部区域,另外还存在一些中间区DAPI带及可变带,总带数为62。PI带型结果与DAPI带型结果相似,在所有染色体上都存在PI阳性带。2种带型的阳性带所在位置与异染色质分布区域相吻合。 相似文献
998.
999.
1000.
This paper uses Landsat TM images, GIS technology, Digital Elevation and Habitat Assessment Models to assess the habitat suitability of the endangered plant Tetraena mongolica in western Ordos Plateau of China by selecting terrain, soil, climate, and human activity factors as assessment indices. The results are as follows: natural factors such as climate and terrain are not restrictive factors for the survival and development of T. mongolica in the research region, whereas human activity causes habitat quality of T. mongolica to change intensively in quantity and distribution. The area of less suitable habitat increased by 23.87 km2 compared to potential habitat suitability. Thus, in some areas, human activity may be a key factor causing the endangerment of T. mongolica. There were obvious differences of potential and practical habitat suitability between different habitat regions in the study area. The habitat quality was better in Wujiamiao, Dishan and Qipanjing regions, and worse in Wuda and Qianlishan regions. 相似文献