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931.
为研究菜田施肥(化肥)对地下水氮污染的影响,进行了2个土柱模拟菜田施肥(化肥)残存量的实验.结果表明,土柱中化肥残存量的72.08%和47.44%从渗出水中流出.依据实验数据将实验过程分为3个可能阶段:第1阶段,化肥中的NH+4被土壤吸附,并交换出土壤中的K++Na+,Ca2+和Mg2+,使之进入渗出水中;第2阶段,为硝化作用增强的阶段,表现为土柱渗出水中NO-3的质量浓度比注入水有大幅度增加;第3阶段,为硝化作用强度减弱的阶段,表现为渗出水中NO-3的质量浓度比注入水增加的幅度减小. 相似文献
932.
The lower valley of Changjiang, from Wuhan of the Hubei Province in the west to Zhenjiang of the Jiangsu Province in the east, contains more than 200 polymetallic (Cu–Fe–Au, Mo, Zn, Pb, Ag) deposits and is one of the most important metallogenic belts in China. This metallogenic belt, situated at the northern margin of the Yangzi craton and bordered by the Dabieshan ultrahigh pressure metamorphic belt to the north, consists mainly of Cambrian–Triassic marine clastic sedimentary rocks and carbonate and evaporite rocks, which overlay a Precambrian basement and are intruded by Yanshanian (205 to 64 Ma) granitoid intrusions and subvolcanic complexes. Repeated tectonism from Late Proterozoic to Triassic resulted in extensively developed networks of faults and folds involving the Cambrian–Triassic sedimentary strata and the Precambrian basement. The Yanshanian granitoid intrusions and subvolcanic complexes in the Lower Changjiang metallogenic belt are characterized by whole-rock δ18O of +8‰ to +10‰, initial 87Sr/86Sr of 0.704 to 0.708, and εNdt from −10 to −17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials. Also, the Yanshanian granitoids exhibit eastward younging and increase in alkalinity (i.e., from older calc–alkaline in the west to younger subalkaline–alkaline in the east), which are related to oblique collision between the Yangzi and Sino-Korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes. Most polymetallic deposits in the Lower Changjiang metallogenic belt are clustered in seven districts where the Yanshanian magmatism is particularly extensive: from west to east, Edong, Jiurui, Anqing–Guichi, Luzhong, Tongling, Ningwu and Ningzhen. Mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits: orebodies in Yanshanian granitoid intrusions, skarn orebodies at the contact zones between the Yanshanian intrusions and Late Paleozoic–Early Mesozoic sedimentary rocks, and stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata. The most important host sedimentary strata are the Middle Carboniferous Huanglong Formation, Lower Permian and Lower–Middle Triassic carbonate and evaporite rocks. The intrusion-hosted and skarn orebodies exhibit well-developed zonation in alteration assemblages, metal contents, and isotopic compositions within individual deposits, and apparently formed from hydrothermal activities related to the Yanshanian magmatism. The stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano-sedimentary exhalative processes in shallow marine environments. However, extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization. On the basis of geological relationships and isotope geochemical characteristics, we propose a carbonate-hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies. This model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the Yanshanian intrusions with carbonate and evaporite wall rocks. Mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion-hosted orebodies. The stratabound massive sulfide deposits of the Lower Changjiang metallogenic belt share many features with the well-studied, high-temperature, carbonate-hosted replacement deposits of northern Mexico and western United States, particularly with respect to association with small, shallow granitoid complexes, structural and stratigraphic controls on mineralization, alteration assemblages, geometry of orebodies, metal association, metal zonation and isotopic systematics. 相似文献
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939.
工程设计Weibull分布参数拟合的改进方法 总被引:2,自引:0,他引:2
董胜 《中国海洋大学学报(自然科学版)》1999,(1)
图解法是求解Weibul分布中3个可调参数的传统方法。但参数的推求过程要图解试求,反复调整,最后结果往往不是最佳拟合参数;线性最小二乘法是最近几年提出的一种求解Weibul分布参数的方法,但其精度受位置参数初始迭代值的影响很大。文中运用麦奎尔特法推求Weibul分布的参数,实现了参数推求的一举寻优。算例表明,拟合方法可行实用,拟合精度明显提高。 相似文献
940.
对三峡数字地震台网记录的2016年3—6月三峡工程库区秭归库段杨林桥镇小震群进行双差精定位,通过Snoke方法计算该震群中较大地震的震源机制解,并结合野外宏观调查等方法,分析震源参数的时空变化特征。结果表明:杨林桥镇小震群密集分布在2 km×3 km矩形范围内,有较明显的展布方向,但与邻近的仙女山断裂、九畹溪断裂和天阳坪断裂走向不一致;震群距长江干流超过10 km,与三峡水库无水利联系,无相关性;震群展布方向上有岩溶洞分布,且降雨丰富,初步判断成因类型为岩溶塌陷型。 相似文献