The Strel’tsovka uranium district: Isotopic geochronological (U-Pb,Rb-Sr,Sm-Nd) characterization of granitoids and their place in the formation history of uranium deposits

An isotopic geochronological study of Russia’s largest Strel’tsovka uranium district has been carried out. Polychronous granite generation, which determined the structure of the pre-Mesozoic basement, had important implications for the formation of volcanotectonic structural elements bearing economic uranium mineralization. The study of U-Pb, Rb-Sr, and Sm-Nd isotopic systems of whole-rock samples and minerals of granitic rocks allowed us to estimate the deportment of these systems in spatially conjugated granite-forming and hydrothermal processes differing in age and gave grounds for revising the age of granites pertaining to the Urulyungui Complex and refining the age of the Unda Complex.     

The south-western Black Forest and the Upper Rhine Graben Main Border Fault: thermal history and hydrothermal fluid flow

The thermal history of the south-westernmost Black Forest (Germany) and the adjacent Upper Rhine Graben were constrained by a combination of apatite and zircon fission-track (FT) and microstructural analyses. After intrusion of Palaeozoic granitic plutons in the Black Forest, the thermal regime of the studied area re-equilibrated during the Late Permian and the Mesozoic, interrupted by enhanced hydrothermal activity during the Jurassic. At the eastern flank of the Upper Rhine Graben along the Main Border Fault the analysed samples show microstructural characteristics related to repeated tectonic and hydrothermal activities. The integration of microstructural observations of the cataclastic fault gouge with the FT data identifies the existence of repeated tectonic-related fluid flow events characterised by different thermal conditions. The older took place during the Variscan and/or Mesozoic time at temperatures lower than 280°C, whereas the younger was probably contemporary with the Cenozoic rifting of the Upper Rhine Graben at temperatures not higher than 150°C.     

Real-time monitoring and early warning of landslides at relocated Wushan Town,the Three Gorges Reservoir,China

A special monitoring and warning system has been established and improved in the Three Gorges Reservoir area since 1999. It is necessary to develop a real-time monitoring system on landslides because there are dense populations centered in the reservoir area and geo-hazards may be triggered by a 30-m water level fluctuation between 145 and 175 m in elevation during reservoir operation; the regular monitoring could not be suitable to the early warning on landslides. Since 2003, the authors have carried out a real-time monitoring and early warning project on landslides at the relocated Wushan town in the Three Gorges Reservoir area. The monitoring station includes Global Positioning System with high-accuracy double frequency to monitor ground displacement, time domain reflection technology, and immobile borehole, inclinometer to monitor deep displacement, piezometer to monitor pore water pressure, and precipitation and reservoir water level monitoring. Compared with traditional methods, the real-time monitoring is continuous and traceable in the acquisition process, and the cycle of data acquisition is very short, usually within hours, minutes, or even shorter. Based on the landslide monitoring experience at the Three Gorges Reservoir area, the early warning criteria on landslide are established in which the critical situation is classified into four levels: blue, yellow, orange, and red, respectively, expressed by no, slight, moderate, and high risk situation. Comprehensive judgment from multimonitoring data of Yuhuangge landslide in this area since 2004 suggested that the new Wushan town will be at the blue early warning level, although some monitoring data of individual displacement at deep borehole showed that the displacement was increased by 5 mm in 5 months with an average velocity of 1.0 mm/month, and the data of BOTDR also showed an obvious dislocation along a stairway on the landslide.     

地层倾角对转换波动校速度分析的影响

动校正速度的求取是三维转换波数据处理的重要环节,其精度高低对转换波的叠加成像质量影响很大。理论上转换波的速度求取受包括界面倾角在内的多种因素影响,但实际应用时这些因素往往被忽略。为证明倾角对动校速度的影响程度,依据前人的研究成果,模拟倾斜地层计算了不同倾角条件下二维测线CCP道集、三维全方位CCP道集PS波动校正速度,并对由不同倾角引起的计算精度差异进行了研究。研究结果表明,对于二维转换波CCP道集,界面倾角不同,动校拉平的速度会差别较大,即使如此也总能实现很大倾角范围内的CCP道集的同相叠加,获得较好的成像质量;对于三维全方位CCP道集,当界面倾角超过一定范围,无论怎样进行精细扫描,得到的都只能是适合特定方位的速度,无法得到适合任意方位的动校扫描速度,随着界面倾角的减小,利用速度扫描的办法可以在一定的偏移距范围内将来自不同方位的记录较平,界面倾角越小,可以校平的偏移距越大;另外由于道集内的地震记录依赖视倾角的动校正速度,在反射界面倾斜的情况下,方位不同,动校正速度不同,致使二维反射PS波资料往往比三维反射PS波资料容易叠加成像。     

高位钻场长钻孔在淮南刘庄煤矿瓦斯抽采中的应用

刘庄煤矿东二采区121102工作面所开采的11-2煤层为非突出煤层,但在工作面回采期间,存在瓦斯突出的可能。为防止工作回风巷尤其是上隅角瓦斯超限,确保工作面的正常生产,同时兼顾瓦斯资源的抽采利用,施工了最大长度496m,钻孔直径133mm的瓦斯抽采孔。实际应用表明,该孔投入使用后,整个工作面回采过程中均未发生过瓦斯超限现象,说明利用大口径长距离钻孔取代巷道抽放瓦斯是完全可行的。本文介绍的高位钻场长钻孔的设计、施工和瓦斯抽采情况,可以为今后同类工作面中长钻孔的施工提供借鉴。     

Two-dimensional horizontal modeling of fine-sediment transport at the South Channel–North Passage of the partially mixed Changjiang River estuary,China

Tidal flow and fine-sediment transport at the South Channel–North Passage of the partially-mixed Changjiang River estuary were studied using a two-dimensional horizontal (2DH) numerical model. This 2DH model was achieved by depth-integrating the momentum and convection–diffusion equations. The Alternating Direction Implicit scheme was used to solve the governing equations. The iterative method was adopted for the calculation of convection and diffusion terms of momentum equation. Comparisons between calculated and measured results (tidal elevations and depth-averaged velocities) have shown reasonable agreement. Horizontal distributions of tidal current velocity and suspended sediment concentration were qualitatively consistent with observations. Those modeled results were analyzed to elucidate the mechanisms for the formation of the turbidity maximum and intratidal variations in fine-sediment transport processes.     

Numerical Simulation of Icing on Nrel 5-MW Reference Offshore Wind Turbine Blades Under Different Icing Conditions

Offshore wind energy resources are operational in cold regions, while offshore wind turbines will face the threat of icing. Therefore, it is necessary to study icing of offshore wind turbines under different icing conditions. In this study, icing sensitivity of offshore wind turbine blades are performed using a combination of FLUENT and FENSAP-ICE software, and the effects of liquid water content (LWC), medium volume diameter (MVD), wind speed and air temperature on blade icing shape are analyzed by two types of ice, namely rime ice and glaze ice. The results show that the increase of LWC and MVD will increase the amount of ice that forms on the blade surface for either glaze ice or rime ice, and an increase of MVD will expand the adhesion surface between ice and blade. Before reaching the rated wind speed of 11.4 m/s, it does not directly affect the icing shape. However, after reaching the rated wind speed, the attack angle of the incoming flow decreases obviously, and the amount of ice increases markedly. When the ambient air temperature meets the icing conditions of glaze ice (i.e., −5°C to 0°C), the lower the temperature, the more glaze ice freezes, whereas air temperature has no impact on the icing of rime ice. Compared with onshore wind turbines, offshore wind turbines might face extreme meteorological conditions, and the wind speed has no impact on the amount of ice that forms on the blade surface for most wind speeds

     

Variations in spring leaf phenology and leaf freezing damage of common woody species in China北大核心CSCD

Freezing damage results in the dehydration of plant cells and reduces the photosynthetic capacity of plants, which causes significant losses to ecology and economy. Over the past 40 years, global warming has reduced the frequency and intensity of frost events while bringing forward the spring phenology of plants, increasing the exposure of their leaves and flowers to harsh cold temperatures. Therefore, the dual effects of climate warming should be considered in order to accurately assess the changes of plant freezing damage. To date, there is no systematic analysis of plant freezing damage in different climatic regions of China. Based on phenological observation records from the China Phenological Observation Network, leaf frost damage of four common woody plants (Ulmus pumila, Robinia pseudoacacia, Salix babylonica, Fraxinus chinensis) in the spring over the past 40 years was calculated, and the spatio-temporal patterns were analyzed. We also investigated the change in the occurrence time of maximum frost damage (TMFD) and its relationship with plant phenology. The results show that: 1) Most species presented an overall trend towards an earlier leaf unfolding date, and the advancing trend was significant and greater than 1 d/a in about 60% of the regions (P<0.05). 2) The TMFD occurred earlier in 72.22%-83.03% of the regions, which was closely related to plants' earlier leaf unfolding date. The TMFD of all species advanced the most (8.3 days) in the temperate climate zone, followed by the warm temperate, subtropical, plateau, and cold temperate zones. 3) The leaves of U. pumila, R. pseudoacacia and S. babylonica suffered more freezing damage in the spring, and the most significant freezing damage was mainly found in the north of 50°N region and part of the west of the Qinghai-Tibet Plateau. In comparison, the leaves of F. chinensis suffered less frost damage due to later leaf unfolding date and stronger leaf frost resistance. With regard to interannual variations, the average freezing damage of U. pumila, R. pseudoacacia and S. babylonica increased significantly (P<0.05), but that of F. chinensis did not change obviously. In addition, the freezing damage of U. pumila and S. babylonica increased the most in the cold temperate zone, while that of R. pseudoacacia increased in about 10% of the regions in the plateau climate zone, and 3%-6% of the regions in the cold temperate, temperate, and warm temperate climate zones. The freezing damage of F. chinensis merely increased in the warm temperate zone. The results of this study can provide a reference for assessing the risk of plant freezing damage accurately and help develop regional-specific response and adaptation strategies to climate change. © 2023, Editorial office of PROGRESS IN GEOGRAPHY. All rights reserved.     

Climate‐driven generation of a fluvial sheet sand body at the Paleocene–Eocene boundary in north‐west Wyoming (USA)

An unusually thick and laterally persistent fluvial sand body crops out at the Paleocene–Eocene boundary within the northern part of the Bighorn Basin in northwest Wyoming, USA. The generation of this ‘Boundary Sandstone’ was previously ascribed to a period of reduced subsidence; however, a new carbon isotope record presented herein shows it to be intimately correlated to the Paleocene–Eocene Thermal Maximum (PETM), an extreme global warming event ca. 56 Ma. This study evaluates the impacts of the PETM on fluvial deposition in the basin by integrating sedimentological data with geochemical, palaeoichnological, and palaeobotanical proxy records. Compared to pre‐ and post‐PETM fluvial sand bodies, the Boundary Sandstone is more highly amalgamated, both vertically and laterally, but shows no changes in lithofacies associations, palaeodispersal directions, palaeoflow depths, or palaeochannel widths. At its thickest, the Boundary Sandstone resides entirely within the main body of the PETM, an ca. 113 kyr time interval when global pCO₂ levels and temperatures were at their highest, and local mean annual rainfall low, floodplains well drained and vegetation comparatively sparse. The totality of data sets imply that the Boundary Sandstone is related to the preferential removal of fine‐grained floodplain deposits by either: (i) rapid readjustments in river gradients related to documented short‐term precipitation oscillations or (ii) reductions in the cohesiveness of overbank sediments related to decreased rooting density and water table fluctuations. Hence, short‐term climate perturbations may manifest within large‐scale depositional patterns in ways ostensibly like tectonics.