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901.
The Danba Structural Culmination is a tectonic window into the late Triassic to early Jurassic Songpan‐Garzê Fold Belt of eastern Tibet, which exposes an oblique section through a complete Barrovian‐type metamorphic sequence. Systematic analysis of a suite of metapelites from this locality has enabled a general study of Barrovian metamorphism, and provided new insights into the early thermotectonic history of the Tibetan plateau. The suite was used to create a detailed petrographic framework, from which four samples ranging from staurolite to sillimanite grade were selected for thermobarometry and geochronology. Pseudosection analysis was applied to calculate PT path segments and determine peak conditions between staurolite grade at ~5.2 kbar and 580 °C and sillimanite grade at ~6.0 kbar and 670 °C. In situ U–Pb monazite geochronology reveals that staurolite‐grade conditions were reached at 191.5 ± 2.4 Ma, kyanite‐grade conditions were attained at 184.2 ± 1.5 Ma, and sillimanite‐grade conditions continued until 179.4 ± 1.6 Ma. Integration of the results has provided constraints on the evolution of metamorphism in the region, including a partial reconstruction of the regional metamorphic field gradient. Several key features of Barrovian metamorphism are documented, including nested PT paths and a polychronic field gradient. In addition, several atypical features are noted, such as PT path segments having similar slopes to the metamorphic field gradient, and Tmax and Pmax being reached simultaneously in some samples. These features are attributed to the effects of slow tectonic burial, which allows for thermal relaxation during compression. While nested, clockwise PTt loops provide a useful framework for Barrovian metamorphism, this study shows that the effects of slow burial can telescope this model in PT space. Finally, the study demonstrates that eastern Tibet experienced a significant phase of crustal thickening during the Mesozoic, reinforcing the notion that the plateau may have a long history of uplift and growth.  相似文献   
902.
特提斯喜马拉雅北亚带江孜地区上古新统-下始新统甲查拉组记录了喜马拉雅碰撞造山带的早期地壳加厚和沉积历史。本文我们报道了甲查拉组详细的碎屑锆石U-Pb年龄和全岩Sm-Nd同位素数据。甲查拉组由青灰色厚层的岩屑砂岩夹泥岩组成,不整合覆盖在宗卓组之上,碎屑锆石主要的峰值介于350~80 Ma, 900~470 Ma以及1 300~950 Ma,次要的峰值介于2 800~1 500 Ma。全岩87Sr/86Sr介于0.707 505~0.713 174,143Nd/144Nd介于0.512 206~0.512 355,εNd(0)介于-5.52~-8.43。甲查拉组物源区以再循环的日喀则弧前盆地和上三叠统郎杰学群为主,少量物质来自雅鲁藏布江缝合带。上述研究表明,甲查拉组沉积在周缘前陆盆地的背景下,且特提斯喜马拉雅北亚带在始新世期间经历了明显的地壳加厚。  相似文献   
903.
印度与欧亚板块碰撞以来东喜马拉雅构造结的演化   总被引:14,自引:0,他引:14  
丁林  钟大赉 《地质科学》2013,48(2):317-333
在野外填图,构造观察及前人研究的基础上,本文识别并描述了东喜马拉雅构造结中的推覆断裂、正断裂及走滑断裂、背斜(形)和向斜(形)等构造类型,讨论了这些构造位置及与印度板块挤入,印支地块旋转的关系,还探讨了东喜马拉雅构造结对印度板块持续向北推挤下的特殊应变调节方式。在印度大陆部分,东喜马拉雅构造结由3个向外逐渐变新的构造结组成,即北东向的南迦巴瓦峰复式背斜、北西向的桑复式向斜及北东向的阿萨母复式向斜。上述3个构造结是协调印度板块的挤入、喜马拉雅弧的扩展及印支地块的旋转的构造。在欧亚大陆内部的冈底斯岛弧,在派区及阿尼桥走滑断裂协调下,高喜马拉雅结晶岩的基底挤入冈底斯岛弧内部,在大拐弯顶端形成向上的挤出构造。在南迦巴瓦峰构造结的北西侧,由于掀斜式抬升及重力滑动,使得冈底斯盖层与结晶基底脱耦,上盘盖层沿东久向北西方向滑动。在南迦巴瓦峰构造结北东侧,由于印支地块的挤出和旋转,形成一系列的北西向走滑断裂,如实皆断裂、嘉黎-高黎贡断裂、澜沧江断裂及红河断裂等。  相似文献   
904.
The cracked chevron-notched Brazilian disc (CCNBD) was proposed by the International Society for Rock Mechanics (ISRM) to test the mode I (opening mode) fracture toughness of rock. The test method has been vigorously discussed and debated, despite being the subject of intensive research for decades. The minimum (critical) dimensionless stress intensity factors affiliated with the formula for calculating the fracture toughness using CCNBD specimens with different geometric parameters remain elusive and complex. The matter cannot be resolved by simply replacing the diameter in the original formula with the radius, as claimed by several authors. In this paper, the formula is fundamentally improved, as wide-ranging minimum dimensionless stress intensity factors pertaining to diversified CCNBD geometries are recalibrated by three-dimensional finite element analysis, and an expression with tabulated coefficients is obtained through curve-fitting the data obtained from the numerical calibration. The present results are shown to be more accurate than those in the literature. Furthermore, the importance of the reasonability of the results is highlighted; a comprehensive comparison of different values shows that the upper bounds of minimum stress intensity factors are violated by the above claim. The confusion resulting from the claim is, thus, clarified conclusively.  相似文献   
905.
In order to better predict the geometry and spatial distribution of reservoir facies and permeability barriers, it is critical to understand stratigraphic geometries and architecture at all scales within a basin. Stratigraphic forward modelling (SFM) allows geologists to forward project the deposition and evolution of sedimentary facies within a stratigraphic framework with given prior boundary conditions. The method can approximate depositional processes while taking into consideration a range of factors that affect basin evolution and sedimentation. This paper presents an overview of recent developments in stratigraphic forward models that are currently available and have been successfully employed in simulating stratigraphic development, including geometric models, diffusion models, Fuzzy Logic models and hydraulic models. In addition, the paper discusses SFM used in the simulation of the behaviour of natural sedimentary systems and verification of the potential for hydrocarbon entrapment and accumulation in a basin using an example from the Ordos Basin, western China.  相似文献   
906.
Numerous ordered defect structures are known that are related to the sodium chloride (or MgO) structure type, thus they are basically cubic closest packed (ccp) arrangements with vacancies. For example the NbO type is an MgO type in which one quarter each of the anions and the cations are missing compared to the ccp in such a way that both anions and cations are in square-planar coordination. In spinel, Al2MgO4, one half of the octahedrally coordinated cations are missing compared with the MgO type and only one eighth of the tetrahedrally coordinated sites within the ccp are occupied. What these cases have in common is that all these derivatives are rather dense. This is different in pharmacosiderite, K[Fe4(OH)4As3O12]. 6 to 7H2O, where one half of the anion positions, three quarters of the octahedral sites and five eighth of the tetrahedral sites remain vacant, compared to the spinel type. Pharmacosiderite is a wide open porous structure with zeolitic properties. We are illustrating these relationships using a Bärnighausen symmetry tree and by tables relating the various structure types to each other.  相似文献   
907.
根据西北黄土地区第一条地铁——西安地铁近四年地铁基坑工程的监测经验,提出了基坑工程监测的主要内容、作用及其常用监测手段,介绍了轴力监测关键技术;测斜仪量测墙体位移关键技术;地裂缝段地表监测点布设的关键技术;盾构地表监测作用、监测项目、地层移动特征;监测报警注意事项。其中着重分析了黄土地区常用的内支撑形式——钢支撑监测的注意事项及常见异常测量数据的出现原因,提出温度对其测量结果的影响不可忽略。  相似文献   
908.
Groundwater flow in a well-developed karst aquifer dominantly occurs through bedding planes, fractures, conduits, and caves created by and/or enlarged by dissolution. Conventional groundwater modeling methods assume that groundwater flow is described by Darcian principles where primary porosity (i.e. matrix porosity) and laminar flow are dominant. However, in well-developed karst aquifers, the assumption of Darcian flow can be questionable. While Darcian flow generally occurs in the matrix portion of the karst aquifer, flow through conduits can be non-laminar where the relation between specific discharge and hydraulic gradient is non-linear. MODFLOW-CFP is a relatively new modeling program that accounts for non-laminar and laminar flow in pipes, like karst caves, within an aquifer. In this study, results from MODFLOW-CFP are compared to those from MODFLOW-2000/2005, a numerical code based on Darcy’s law, to evaluate the accuracy that CFP can achieve when modeling flows in karst aquifers at laboratory and sub-regional (Woodville Karst Plain, Florida, USA) scales. In comparison with laboratory experiments, simulation results by MODFLOW-CFP are more accurate than MODFLOW 2005. At the sub-regional scale, MODFLOW-CFP was more accurate than MODFLOW-2000 for simulating field measurements of peak flow at one spring and total discharges at two springs for an observed storm event.  相似文献   
909.
在钻井岩心观察和岩石学分析的基础上,对川中东北部龙岗地区中-下侏罗统自流井组和凉高山组典型钻井取心段碳酸盐岩样品进行了碳氧同位素分析。40余件样品的测试结果表明,δ13CPDB值在-1.24‰~4.59‰之间,除了1个负值外,都为正值。δ18OPDB值在-15.7‰~-9.83‰之间,都为负值。与海相和陆相碳酸盐岩同位素值对比显示,自流井期和凉高山期古湖泊均表现出内陆开放性淡水湖泊的特点,没有经过明显的海水入侵。在中-下侏罗统广泛存在的碳同位素正偏移是由湖泊初级生产力提高所导致的。岩相和同位素变化显示了古湖平面经历了2次主旋回和6次次级旋回变化,湖平面变化总体表现为东岳庙段沉积期>大一三亚段沉积期>大一亚段沉积期>凉高山期>马鞍山段沉积期。古湖泊初级生产力的变化表现为大一三亚段沉积期>东岳庙段沉积期>大一亚段沉积期>凉高山期>马鞍山段沉积期。  相似文献   
910.
Effects of inhibitors on uptake and assimilation of ferricyanide by different plants were investigated. Detached roots of plants were kept in a closed-dark hydroponic system with ferricyanide solution amended with various inhibitors. Dissociation of ferricyanide to free cyanide and iron in solution was negligible. The application of inhibitors affected both botanical assimilation and uptake of ferricyanide. Of the inhibitors tested, silver nitrate showed a significantly inhibitory effect on ferricyanide uptake by rice, soybean and maize (P < 0.01), while a negligible effect was found in willows spiked with the same inhibitor (P > 0.05). However, lanthanum chloride showed the most severe effect on botanical assimilation of ferricyanide by maize and rice (P < 0.01), whereas silver nitrate and tetraethylammonium chloride were the most sensitive inhibitors to soybean and willows, respectively (P < 0.01). Botanical assimilation of ferricyanide was observed positively in responses to temperatures, in which maize was more susceptible than other selected plants. In conclusion, application of inhibitors has a substantial influence on the uptake and assimilation of ferricyanide by plants, and the inhibitory efficiency is highly dependent on the species of inhibitors applied.  相似文献   
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