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101.
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郯庐断裂带张八岭隆起段晚中生代岩浆岩继承锆石U-Pb年代学:源区属性及构造意义 总被引:1,自引:0,他引:1
大别与苏鲁造山带之间的郯庐断裂带张八岭隆起段,构成了华北与扬子板块之间的断裂边界。该边界带的深部结构状态长期以来存在着不同的认识。本文利用张八岭隆起带沿线出露的晚中生代岩浆岩中继承锆石U-Pb年代学信息,结合地球物理资料及Nd、Pb、Hf同位素资料,分析了其深部的岩浆源区属性及结构状态。张八岭隆起带北段晚中生代岩浆岩继承锆石年龄以1.9~2.7Ga为主,最大峰值年龄为2.5Ga;南段继承锆石年龄以2.2~2.6Ga为主,峰值年龄也为2.5Ga;郯庐断裂带庐江段则以含大量新元古代锆石为特征,在0.7Ga形成显著的分布峰值,并有早元古和少量太古代年龄信息。分析结果表明,张八岭隆起带北段的晚中生代岩浆岩源区为华北下地壳,南段的源区兼有华北和扬子陆壳的信息,而更南部庐江段则以扬子地壳源区为特征。电法剖面揭示,郯庐断裂主边界在张八岭隆起带下向南东倾斜,从而深部存在华北地壳;而南部庐江段转变为向北西陡倾,从而深部皆为扬子地壳。郯庐断裂深部产状特征支持其印支期应为斜向汇聚边界。而其中三叠纪继承锆石的缺失指示隆起带上变质岩应为原地岩石,而非来自大别造山带。 相似文献
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Juan Pérez Quezadas Victor M. Heilweil Alejandra Cortés Silva Luis Araguas María del Rocío Salas Ortega 《Hydrogeology Journal》2016,24(8):1953-1966
Geochemistry and environmental tracers were used to understand groundwater resources, recharge processes, and potential sources of contamination in the Rio Actopan Basin, Veracruz State, Mexico. Total dissolved solids are lower in wells and springs located in the basin uplands compared with those closer to the coast, likely associated with rock/water interaction. Geochemical results also indicate some saltwater intrusion near the coast and increased nitrate near urban centers. Stable isotopes show that precipitation is the source of recharge to the groundwater system. Interestingly, some high-elevation springs are more isotopically enriched than average annual precipitation at higher elevations, indicating preferential recharge during the drier but cooler winter months when evapotranspiration is reduced. In contrast, groundwater below 1,200 m elevation is more isotopically depleted than average precipitation, indicating recharge occurring at much higher elevation than the sampling site. Relatively cool recharge temperatures, derived from noble gas measurements at four sites (11–20 °C), also suggest higher elevation recharge. Environmental tracers indicate that groundwater residence time in the basin ranges from 12,000 years to modern. While this large range shows varying groundwater flowpaths and travel times, ages using different tracer methods (14C, 3H/3He, CFCs) were generally consistent. Comparing multiple tracers such as CFC-12 with CFC-113 indicates piston-flow to some discharge points, yet binary mixing of young and older groundwater at other points. In summary, groundwater within the Rio Actopan Basin watershed is relatively young (Holocene) and the majority of recharge occurs in the basin uplands and moves towards the coast. 相似文献
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Linear discriminant analysis to describe the relationship between rainfall and landslides in Bogotá, Colombia 总被引:1,自引:0,他引:1
Alfonso Mariano Ramos-Cañón Luis Felipe Prada-Sarmiento Mario Germán Trujillo-Vela Juan Pablo Macías Ana Carolina Santos-R 《Landslides》2016,13(4):671-681
Bogotá is located in the central Andean region of Colombia, which is frequently affected by landslide processes. These processes are mostly triggered during the rainy season in the city. This fact remarks the importance of determining what rain-derived parameters (e.g. intensity, antecedent rain, daily rain) are better related with the occurrence of landslides. For this purpose, the linear discriminant analysis (LDA), a technique derived from multivariate statistics, was used. The application of this type of analysis led to obtain simple mathematical functions that represent the probability of occurrence of landslides in Bogotá. The functions also allow to identify the most relevant variables derived from records of rainfall linked to the generation of landslides. A proof of concept using the proposed methodology was done using historic rainfall data from a 9-km2 area of homogenous climatology and geomorphology in the south part of Bogotá. Landslides needed to be grouped for the LDA. Each one of these grouping categories represents landslides that occurred in similar geomorphologic conditions. Another set of events with no landslides was generated synthetically. Results of the proof of concept show that rainfall parameters such as normalized rainfall intensity I MAP, normalized daily rainfall R MAP and rainy-days normal RDN have the best statistical correlation with the landslides observed in the zone of analysis. 相似文献
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Based on Hencky’s total strain theory of plasticity, ultimate bending capacity of steel pipes can be determined analytically assuming an elastic-linear strain hardening material, the simplified analytical solution is proposed as well. Good agreement is observed when ultimate bending capacities obtained from analytical solutions are compared with experimental results from full-size tests of steel pipes. Parametric study conducted as part of this paper indicates that the strain hardening effect has significant influence on the ultimate bending capacity of steel pipes. It is shown that pipe considering strain hardening yields higher bending capacity than that of pipe assumed as elastic-perfectly plastic material. Thus, the ignorance of strain hardening effect, as commonly assumed in current codes, may underestimate the ultimate bending capacity of steel pipes. The solutions proposed in this paper are applicable in the design of offshore/onshore steel pipes, supports of offshore platforms and other tubular structural steel members. 相似文献
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Grajales-Nishimura José Manuel Ramos-Arias Mario Alfredo Solari Luigi Murillo-Muñetón Gustavo Centeno-García Elena Schaaf Peter Torres-Vargas Ricardo 《International Journal of Earth Sciences》2018,107(3):1005-1031
International Journal of Earth Sciences - The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated... 相似文献