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991.
对2006年10月采自长江巫山段一级支流大宁河河底的三根岩芯作了常量元素(K、Na、Ca、Mg)的分析。研究结果表明,沉积物中稀酸可溶相常量元素的含量能够反映沉积物的特征和来源。大宁河中—上游沉积物中碳酸盐含量平均为23%,反映岩溶地区石灰岩风化的影响;而与长江交接处的沉积物中碳酸盐含量平均为10%,显示长江主流有明显不同的沉积物来源。三峡大坝的建成蓄水,水位提高,使得碳酸盐含量低的红色粘土进入双龙镇段大宁河沉积,造成碳酸盐含量、稀酸可溶相常量元素含量急剧下降、沉积物的颜色发生显著变化。受到蓄水作用的影响,大宁河泥沙沉积速率大幅度提高,自2004年12月蓄水以来,大宁河双龙镇附近沉积物厚达10cm以上。 相似文献
992.
993.
Chemical weathering was investigated by collecting samples from five selected weathering profiles in a high elevation granitic
environment located in Seoul, Korea. The overall changes of chemistry and mineralogical textures were examined reflecting
weathering degrees of the samples, using polarization microscopy, X-ray diffraction (XRD), electron probe micro analysis (EPMA),
X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma–mass spectroscopy (ICP–MS). The chemical distribution
in the weathering profiles shows that few trace elements are slightly immobile, whereas most major (particularly Ca and Na)
and trace elements are mobile from the beginning of the granite weathering. On the other hand, there were mineralogical changes
initiated from a plagioclase breakdown, which shows a characteristic circular dissolved pattern caused by a preferential leaching
of Ca cation along grain boundaries and zoning. The biotite in that region is also supposed to be sensitive to exterior environmental
condition and may be easily dissolved by acidic percolated water. As a result, it seems that some rock-forming minerals in
the granitic rock located in Seoul are significantly unstable due to the environmental condition of acidic rainfall and steep
slopes, where they are susceptible to be dissolved incongruently leading some elements to be highly depleted. 相似文献
994.
Petrogenesis of Volcanic Rocks from Saipan and Rota, Mariana Islands, and Implications for the Evolution of Nascent Island Arcs 总被引:2,自引:0,他引:2
Reagan Mark K.; Hanan Barry B.; Heizler Matthew T.; Hartman Brian S.; Hickey-Vargas Rosemary 《Journal of Petrology》2008,49(3):441-464
An 40Ar/39Ar age of 45·1 Ma determined for lavas fromnorthern Saipan confirms that these high-silica rhyolites eruptedduring the proto-arc stage of volcanism in theIzu–Bonin–Mariana system, which is characterizedelsewhere by eruption of boninitic lavas. Incompatible traceelement concentrations and Sr, Hf, Nd, and Pb isotope ratiosfor these rhyolites are transitional between those of c. 48Ma boninitic lavas and post-38 Ma first-arc andesitesand dacites from Saipan and Rota that have typical subduction-relatedcompositions. These transitional compositions are modeled bycrystal fractionation of parental tholeiitic basalt combinedwith assimilation of young boninitic crust. A second stage ofRayleigh fractionation in the upper crust is required by SiO2concentrations that exceed 77 wt % and near-zero compatibleelement concentrations. First-arc magma compositions are consistentwith fractionation of basalt and assimilation of crust similarin composition to the first-arc magmas themselves. The mantlesources of the proto-arc and first-arc lavas from Saipan andRota are similar to those of Philippine back-arc basin basaltsbased on Nd and Hf isotopic compositions. The Pb isotope compositionsof these lavas are between those of Pacific sea-floor basaltsand Jurassic and younger cherty and clay-rich sediments. Thiscontrasts with the boninitic proto-arc volcanic rocks from Guamand Deep Sea Drilling Project Sites 458 and 459 that have Pbisotope compositions similar to Pacific basin basalts and volcaniclasticsediments. The preferred explanation for the difference in thenature of proto-arc volcanism between Saipan and other fore-arclocations is that the crust ceased extending 3–4 Myr earlierbeneath Saipan. This was caused by a change from mantle upwelling,fore-arc extension, and shallow melting to an environment dominatedby more normal mantle wedge convection, stable crust, and deepermelting. KEY WORDS: rhyolite; andesite; Mariana arc; isotope ratios; trace elements 相似文献
995.
Distribution Characteristics of Sulfur and the Main Harmful Trace Elements in China's Coal 总被引:1,自引:1,他引:0
To promote the rational development and use of clean coal resources in China,data on the regional and age distribution of sulfur,arsenic and other harmful elements in Chinese coal was broadly collected,tested for content,and analyzed.Coal in northwestern China is characterized by low to extremely low levels of sulfur;the coal of the Taiyuan Formation in northern China mainly has high-sulfur content;that of the Shanxi Formation is mainly characterized by low sulfur coal;and the Late Permian coal in southern China has overall higher sulfur content;other regions have low sulfur coal.The average content of harmful trace elements in the bulk of China's coal is similar to the corresponding content in the coal of the North America and the rest of the world,whereas the content of various elements(Hg,Sb and Se)is different in magnitude to the corresponding percentage in the crust.The average content of the elements Cr,Se,Co,Be,U,Br in Late Permian coal in S China ranks first in the country whereas the average content of Hg and Cl in the coals of Late Carboniferous to Early Permian age in N China are the highest.The average content of Mn in Early and Middle Jurassic coal is higher in NW China.The high content of harmful elements in some coal should cause particular concern both in the development and utilization of coal. 相似文献
996.
针对航空高光谱数据几何畸变严重的问题,该文探索了利用POS数据辅助航空高光谱影像几何校正的研究现状,分析了基于POS系统的导航数据的线阵推扫高光谱数据解算成像瞬间外方位元素的原理,以及行方位数据支持的线中心投影影像通过改进的共线方程方法几何校正的过程,实现了无地面控制点数据的直接几何校正。采用高光谱影像分块处理方法,实现了高吞吐快速几何校正。HySpex SWIR-384高光谱影像的实验结果表明,该文的校正算法可达到9.15m的绝对定位精度,最终利用少量地面控制点进行几何精校正,其均方根误差达到0.93m。 相似文献
997.
武汉市城市空间集聚要素的分布特征与模式 总被引:12,自引:3,他引:9
不同城市要素的集聚现象具有不同的空间模式,定量化研究城市要素集聚模式的差异和联系对于理解城市发展机理、合理制定城市规划具有重要意义。本文以武汉市为例,获取不透水表面、商业服务业网点(POI)、人口、容积率、城市道路等城市要素数据;采用核密度估计法识别城市主次中心,从城市要素的分布形态、集聚程度、集聚模式等来研究城市要素的空间分布格局特征。研究发现,武汉市呈现“一主七副”的多中心结构,各城市要素从城市中心向外呈反S型的圈层递减。采用集聚度指数衡量城市要素的集聚水平,结果显示商业POI、人口密度的集聚程度最大,其次是容积率、道路密度、不透水表面占比。高度集聚的商业POI、人口密度呈现出点状模式与带状模式相结合的分布模式,中度集聚的道路密度、容积率呈现点状模式、环状模式与轴状模式相结合的分布模式,低度集聚的不透水表面密度主要表现为环状模式。城市中心的吸引、立体空间开发等促进了城市要素的向心集聚,交通干线、稀缺景观资源的廊道效应等重塑了城市要素的空间分布形态。 相似文献
998.
宝鸡市重点景区游客满意度评价研究 总被引:2,自引:0,他引:2
重点景区在目的地城市的旅游资源功能发挥中扮演着重要角色.构建宝鸡市重点景区期望差异理论模型,通过李克特五级量表调查游客的游前期望和游后的实际感知,对宝鸡市八大不同级别的重点旅游景区进行分析,得到游客满意度的优势和劣势因子.结果表明:游客对宝鸡旅游总体感到较为满意,旅游资源禀赋好但分布较散,难以满足多元化旅游者的需求;餐饮卫生、住宿便捷度、购物环境和种类、历史文化特色四大类因子的游客期望和实际感知差异值均为负,在景区发展中处于弱势;与法门寺相比,太白山更具有资源和观赏优势,其余景区的观赏价值虽较高,但整体满意度不均衡.针对弱势因子探讨并提出解决对策,为宝鸡市旅游业健康、快速发展提供借鉴. 相似文献
999.
1000.
Wang Mingyu The University of Arizona Tucson Arizona USA Department of Water Resources Environmental Engineering China University of Geosciences Beijing Chen Jinsong Wan Li Department of Water Resources Environmental Engineering 《中国地质大学学报(英文版)》2001,12(3)
INTRODUCTIONGroundwaterorfluidflowmodelinginfracturedrocksisacomplicatedtheoreticalandappliedtopic.Boththeoreticallyandoperationally ,itisimportantinmanyfieldssuchasgeologicalandhydrogeologicalengineering ,environmentalengineeringandpetroleumengineerin… 相似文献