扬子地块西缘峨山新元古代A2型花岗闪长岩的成因及构造意义

在扬子地块西缘出露有大量的新元古代岩浆岩,这些岩石对于重建罗迪尼亚超大陆有着重要的意义。本文对云南峨山岩体的花岗闪长岩和似斑状黑云母二长花岗岩开展了详细的岩石学、岩石地球化学和年代学研究,结果表明,似斑状黑云母二长花岗岩侵位于826.6±2.5 Ma,而花岗闪长岩有着较年轻的结晶年龄818.3±2.8 Ma,花岗闪长岩比似斑状黑云母二长花岗岩有着更低的SiO₂含量,但是更高的Al₂O₃、MgO、Fe₂O₃、TiO₂和P₂O₅含量。在稀土元素配分曲线和微量元素蛛网图上,两种岩性呈现出相似的特征,都是具有右倾的稀土元素配分样式,呈现出Eu负异常,相对于大离子亲石元素（LILEs）更亏损高场强元素（HFSEs）。似斑状黑云母二长花岗岩富集Nd同位素组分,而花岗闪长岩与之有着相似的Nd同位素值。地球化学数据显示可能的岩石学成因是变质火成岩源区在826 Ma时发生部分熔融形成了峨山似斑状黑云母二长花岗岩并且残留下来了一个麻粒岩化的源区;麻粒岩源区在818 Ma时再次发生部分熔融形成了具有A型属性的峨山花岗闪长岩。结合前人的数据和本文的研究,认为扬子西缘在新元古代时期是一个活动大陆边缘,而华南地块当时在罗迪尼亚的位置更可能是在边缘而不是中心。     

基于遥感的大兴安岭小扬气镇用地类型变化及生态环境状况评价

大兴安岭小扬气镇位于大兴安岭南部,属大小兴安岭森林生态功能区,森林覆盖率高,湿地资源丰富,曾是木材生产基地。为掌握小扬气镇用地类型现状及其变化,开展生态状况评价,利用多源卫星遥感数据,通过多尺度图像分割、决策树及目视解译等方法分别对该区1985年、1998年、2008年和2018年土地利用类型进行提取,计算生态环境状况指数(I_E),评价生态环境状况。结果表明: 小扬气镇土地利用类型以林地、沼泽、水域为主,三者占研究区总面积的97%以上; 沼泽草地主要由阔叶林转化而来,耕地主要由阔叶林、沼泽草地转化而来,草地主要转化为阔叶林、沼泽草地,阔叶林与沼泽草地之间的相互转化最为剧烈; 新增工矿仓储用地主要占用了原有阔叶林土地,新增住宅用地主要占用了原有的沼泽草地、阔叶林、森林沼泽等。总体来看,区内生态环境状况良好,在维护生态安全、促进当地绿色经济发展中起到了重要作用。     

批判实在论在城市空间研究中的应用

批判实在论是一种有关社会科学的哲学理论,它从浅显易懂的本体论出发,抨击了传统科学研究中背离客观实在的种种理想主义倾向,如对“规律性”的迷信、对计量分析方法的过分依赖等。在上世纪80年代批判实在论被引入到西方城市空间研究中、发展为一种新的研究范式,该范式在对传统空间分析研究的批判基础上强调对空间现象的因果机制的阐释,提出了有关因果机制的概念框架,认为只有透过错综复杂的因果关系去把握决定事物的深层结构和机制,才能避免传统研究中常出现的“混乱归因”现象,为此发展了具体研究和抽象研究、深入研究和广泛研究相结合的研究方法,并将其应用于城市空间研究实践中。本研究对批判实在论范式的产生背景和哲学基础等进行了分析,介绍了其理论脉络、方法论和研究实践,并对该范式进行了评价。     

Early solar system aqueous activity: K isotope evidence from Allende

The alkali element K is moderately volatile and fluid mobile; thus, it can be influenced by both primary processes (evaporation and recondensation) in the solar nebula and secondary processes (thermal and aqueous alteration) in the parent body. Since these primary and secondary processes would induce different isotopic fractionations, K isotopes could become a potential tracer to distinguish them. Using recently developed methods with improved precision (0.05‰, 95% confidence interval), we systematically measured the K isotopic compositions and major/trace elemental compositions of chondritic components (18 chondrules, 3 CAIs, 2 matrices, and 5 bulks) in the carbonaceous chondrite fall Allende. Among all the components analyzed in this study, CAIs, which formed initially under high‐temperature conditions in the solar nebula and were dominated by nominally K‐free refractory minerals, have the highest K₂O content (average 0.53 wt%) and have K isotope compositions most enriched in heavy isotopes (δ⁴¹K: ?0.30 to ?0.25‰). Such an observation is consistent with previous petrologic studies that show CAIs in Allende have undergone alkali enrichment during metasomatism. In contrast, chondrules contain lower K₂O content (0.003–0.17 wt%) and generally lighter K isotope compositions (δ⁴¹K: ?0.87‰ to ?0.24‰). The matrix and bulks are nearly identical in K₂O content and K isotope compositions (0.02–0.05 wt%; δ⁴¹K: ?0.62 to ? 0.46‰), which are, as expected, right in the middle of CAIs and chondrules. This strongly indicates that most of the chondritic components of Allende suffered aqueous alteration and their K isotopic compositions are the ramification of Allende parent‐body processing instead of primary nebular signatures. Nevertheless, we propose the small K isotope fractionations observed (< 1‰) among Allende components are likely similar to the overall range of K isotopic fractionation that occurred in nebular environment. Furthermore, the K isotope compositions seen in the components of Allende in this study are consistent with MC‐ICP‐MS analyses of the components in ordinary chondrites, which also show an absence of large (10‰) isotope fractionations. This is not expected as evaporation experiments in nebular conditions suggest there should be large K isotopic fractionations. Nevertheless, possible nebular processes such as chondrules back exchanging with ambient gas when they formed could explain this lack of large K isotopic variation.     

盘西线新海站至大塘站岩溶路基塌陷发育规律及注浆整治

通过对盘西线新海站—大塘站(K 3 500~K 38 493)岩溶路基塌陷病害注浆整治的实例,介绍了该段岩溶路基塌陷发育规律、病害情况、病害的形成机理、注浆整治方法、质量检查方法等内容。     

Migration and speciation transformation mechanisms of mercury in undercurrent zones of the Tongguan gold mining area,Shaanxi Loess Plateau and impact on the environment

In order to study the migration and transformation mechanism of Hg content and occurrence form in subsurface flow zone of gold mining area in Loess Plateau and its influence on water environment, the field in-situ infiltration test and laboratory test were carried out in three typical sections of river-side loess, alluvial and proluvial strata in Tongguan gold mining area of Shaanxi Province, and the following results were obtained: (1) The source of Hg in subsurface flow zone is mainly caused by mineral processing activities; (2) the subsurface flow zone in the study area is in alkaline environment, and the residual state, iron and manganese oxidation state, strong organic state and humic acid state of mercury in loess are equally divided in dry and oxidizing environment; mercury in river alluvial or diluvial strata is mainly concentrated in silt, tailings and clayey silt soil layer, and mercury has certain stability, and the form of mercury in loess is easier to transform than the other two media; (3) under the flooding condition, most of mercury is trapped in the silt layer in the undercurrent zone where the sand and silt layers alternate with each other and the river water and groundwater are disjointed, and the migration capacity of mercury is far less than that of loess layer and alluvial layer with close hydraulic connection; (4) infiltration at the flood level accelerates the migration of pollutants to the ground; (5) the soil in the undercurrent zone is overloaded and has seriously exceeded the standard. Although the groundwater monitoring results are safe this time, relevant enterprises or departments should continue to pay attention to improving the gold extraction process, especially vigorously rectify the small workshops for illegal gold extraction and the substandard discharge of the three wastes, and intensify efforts to solve the geological environmental problems of mines left over from history. At present, the occurrence form of mercury in the undercurrent zone is relatively stable, but the water and soil layers have been polluted. The risk of disjointed groundwater pollution can not be ignored while giving priority to the treatment of loess and river alluvial landform areas with close hydraulic links. The research results will provide a scientific basis for water conservancy departments to groundwater prevention and control in water-deficient areas of the Loess Plateau.     

Flexural performances of prestressed high strength concrete piles reinforced with hybrid GFRP and steel bars

Abstract

This study developed prestressed high-strength concrete (PHC) piles reinforced with high-strength materials (glass fiber-reinforced polymer (GFRP) bars) for flexural performance enhancement. Flexural strengths and behaviors of PHC piles reinforced with hybrid GFRP and steel bars were experimentally investigated, respectively. Large-scale specimens with total lengths of 12,000?mm and diameters of 600?mm were constructed and tested under bending, accompanied by evaluation of effects of non-prestressed reinforcement type and longitudinal reinforcement ratio. J-factors were calculated to evaluate deformability of all the specimens. PHC piles reinforced with GFRP bars were demonstrated to have much higher flexural capacity than those reinforced with steel bars. Moreover, strains at the midspans of cross sections of all the specimens basically conformed to the assumption of plane section. Failure of PHC piles reinforced with GFRP bars was attributable to gradual concrete crushing, while that of PHC piles reinforced with steel bars resulted from steel yielding. Results of this study were expected to provide theoretical basis for wide engineering applications of PHC piles reinforced with hybrid GFRP bars and steel bars in marine structures.     

Dynamic characteristics of marine soft clay under variable phase difference and initial static shear stress

Abstract

Under seismic loading, the soil layer is subjected to multidirectional cyclic shear stress with different amplitudes and frequencies because of the coupling of multiple shear waves and the soil element within a slope or behind a retaining wall is subjected to initial static shear stress before subjected to cyclic loading. Due to the complexity of seismic loading propagation, a phase difference exists between the initial static shear stress and cyclic shear stress. To investigate the influence of the phase difference and initial static shear stress on cyclic shear strain, cyclic modulus, and cyclic strength, a series of laboratory tests are performed on Wenzhou marine soft clay by multi-directional simple shear system, which can simulate the actual state better by controlling the horizontal cyclic stress in the x and y directions simultaneously. As the phase difference varies from 0° to 90°, the dynamic shear modulus increases and cyclic strain accumulation decreases with an increasing number of cycles. The shear strain increases with the initial shear stress.     

Effect of the Coefficient on the Performance of A Two-Layer Boussinesq-Type Model

The coefficients embodied in a Boussinesq-type model are very important since they are determined to optimize the linear and nonlinear properties.In most conventional Boussinesq-type models,these coefficients are assigned the specific values.As for the multi-layer Boussinesq-type models with the inclusion of the vertical velocity,however,the effect of the different values of these coefficients on linear and nonlinear performances has never been investigated yet.The present study focuses on a two-layer Boussinesq-type model with the highest spatial derivatives being 2 and theoretically and numerically examines the effect of the coefficient on model performance.Theoretical analysis show that different values for(0.13≤α≤0.25)do not have great effects on the high accuracy of the linear shoaling,linear phase celerity and even third-order nonlinearity for water depth range of 0相似文献   

贵州罗甸纳饶剖面石炭系维宪阶-谢尔普霍夫阶界线附近的有孔虫

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