Early J2 basalts in SE China: Incipience of large-scale late Mesozoic magmatism

Magmatism in SE China was dormant during 204–180 Ma, but was reactivated in 180–170 Ma (early J₂), and then became more and more intensive towards the end of early Cretaceous. The small-scale early J₂ magmatism is the incipience to long-term and large-scale magmatism in this region. A near east-west (EW) trend volcanic belt was distributed across south Hunan, south Jiangxi and southwest Fujian was formed during early J₂ time. Along this belt from the inland toward the coast, the lithology of basalts changes from alkali into tholeiite, and the amount of erupted volcanic rocks and the proportions of rhyolites coexisting with the basalts increase. On the basis of geochemical characteristics of these basalts, we infer that the melting degree of source rocks and the extent of fractional crystallization and crustal contamination all increased whereas the depth of mantle source decreased from the inland to the coast, which led to the variations of geological characteristics of the volcanic belt. In early J₂, the western spreading Pacific plate began to subduct underneath SE China continental block, reactivating near EW trend deep fault that was originally formed during the Indosinian event. The stress of the western spreading Pacific plate and the extent of asthenosphere upwelling increased from the inland to the coast, which is consistent with the generation and evolution of early J₂ basalts.     

Transformation relationship among different magnetic minerals within loess-paleosol sediments of the Chinese Loess Plateau

The dominant magnetic minerals and carriers of magnetic signals within the Chinese Loess Plateau are magnetite, maghemite, hematite, and goethite. In this study, we investigated the provenance and evolution of magnetic minerals during loess pedogenesis, using X-ray diffraction (XRD) and optical and electron microscopy, including field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Our results reveal that single- and multiphase mineral assemblages among magnetic minerals in the loess-paleosol sequence have been formed. Partial oxidation of coarse eolian magnetite has occurred in the desert source area and the oxidation degree is enhanced after deposition of the dust upon the Chinese Loess Plateau. This mode of origin resulted in a microtexture consisting of an inner magnetite core surrounded by a hematite rim, and strongly affected the magnetic characteristics of the loess. Goethite coexists with hematite in the loess and paleosol, and nanometer-scale hematite is formed upon goethite rims via dehydration. Our study provides direct mineralogical evidence of the magnetic record and paleoclimatic implications of the loess-paleosol sequence of the Chinese Loess Plateau. Supported by National Natural Science Foundation of China (Grant Nos. 40772032 and 40573054) and National Basic Research Program (Grant No. 2007CB815603)     

Gas Emission and Soil Chemical Properties Associated with Underground Coal Fires,Wuda Coalfield,Inner Mongolia,China

Natural Resources Research - The coal fire area in the Wuda coalfield is divided into four parts based on the degree of burning and on surface characteristics: sub-area B is characterized by...     

近50年中国地面气候变化基本特征

采用国家基准气候站和基本气象站的地面资料,系统地分析了中国大陆地区1951年以来近地表主要气候要素演化的时间和空间特征。结果表明,中国近50 a来年平均地表气温变暖幅度约为1.1℃,增温速率接近0.22℃/(10 a),比全球或半球同期平均增温速率明显偏高。地表气温增暖主要发生在最近的20余年,其季节和空间特征与前人分析结论基本一致。降水量变化趋势对所取时间段和区域范围敏感。1951年以来全国平均降水量变化趋势不明显,但1956年以来略有增加。降水变化的空间特征明显而相对稳定,东北北部、包括长江中下游的东南部地区和西部广大地区降水增加,而华北地区以及东北东南部和西北东部地区降水明显减少。分析还发现,近50a来全国平均的日照时数、平均风速、水面蒸发等气候要素均呈显著下降趋势,但积雪地带的最大积雪深度却有所增加。中国日照时间和水面蒸发量变化的空间特征很相似,减少最明显的地区均发生在华北和华东,新疆次之。影响中国年代以上尺度气候变化的因子错综复杂,人类活动引起的大气中温室气体浓度增高可能在一定程度上影响了中国近50 a来的气候,但考虑到尚存的不确定性,目前仍不能给出明确结论。中国东部大部分地区日照时间和水面蒸发量减少可能均起源于人为排放的气溶胶影响,平均风速减弱也有利于水面蒸发量下降,而在西部地区云量和降水量的变化可能更重要。     

一次湖北暴雪天气的诊断与模拟

利用NCEP GFS资料分析了2007年1月15—16日鄂东南地区降雪过程,对造成暴雪过程的天气系统发生、发展背景场进行分析。并利用中尺度数值天气模式WRF模拟了这次暴雪过程,探讨了其发生发展的机制。天气系统的背景分析表明,这次暴雪过程主要是受700 hPa西南急流和地面冷空气的共同影响而产生的,降水过程与西南急流的变化密切联系。WRF模式较好地再现了此次暴雪的过程。模拟结果表明西南急流的减弱和移出,对应着降雪的开始和停止;在西南急流的左侧,由于低层涡度的增加,使低空辐合、高空辐散,在连续性原理和动力机制约束下导致上升运动的加强是该次暴雪的形成机制。模式结果说明,产生暴雪的上升运动要远小于产生暴雨的上升运动,且在暴雪过程中,中层为上升运动,近地层和高层伴随着下沉运动。     

Dynamic interaction of bridge–train system under non‐uniform seismic ground motion

The probability that an earthquake occurs when a train is running over a bridge in earthquake‐prone regions is much higher than before, for high‐speed railway lines are rapidly developed to connect major cities worldwide. This paper presents a finite element method‐based framework for dynamic analysis of coupled bridge–train systems under non‐uniform seismic ground motion, in which rail–wheel interactions and possible separations between wheels and rails are taken into consideration. The governing equations of motion of the coupled bridge–train system are established in an absolute coordinate system. Without considering the decomposition of seismic responses into pseudo‐static and inertia‐dynamic components, the equations of motion of the coupled system are formed in terms of displacement seismic ground motions. The mode superposition method is applied to the bridge structure to make the problem manageable while the Newmark‐β method with an iterative computation scheme is used to find the best solution for the problem concerned. Eight high‐speed trains running over a multi‐span steel truss‐arch bridge subject to earthquakes are taken as a case study. The results from the case study demonstrate that the spatial variation of seismic ground motion affects dynamic responses of the bridge–train system. The ignorance of pseudo‐static component when using acceleration seismic ground motions as input may underestimate seismic responses of the bridge–train system. The probability of separation between wheels and rails becomes higher with increasing train speed. Copyright © 2011 John Wiley & Sons, Ltd.     

郯庐断裂带的伸展活动及其动力学背景

郯庐断裂带的伸展活动发生于晚白垩世至早第三纪,控制形成了-系列断陷盆地.安徽段的断陷出现在晚白垩世至早第三纪,苏鲁段仅发生于晚白垩世,而山东潍坊以北的断陷皆出现在早第三纪,显示了伸展活动南早北晚的迁移规律.这一伸展活动叠加在前期走滑构造之上,呈现为幕式的正断层运动.现可鉴别出断裂带的伸展活动经历过5次显著的断陷事件.郯庐断裂带的伸展构造多不同于典型的裂谷.它与中国东部同期一系列伸展盆地形成的动力学背景一致,是太平洋板块向西正面高角度俯冲下、中国东部岩石圈上拱中出现的巨型伸展构造.     

测绘工程专业“测绘管理”课程教学探讨

结合“测绘管理”课程的教学实践,针对测绘工程专业的培养目标和注册测绘师制度对人才的要求,论述了“测绘管理”课程的课程目标、课程特点和教学要求,对教学设计进行了较为深入的探讨,最后提出了几条教学建议.     

The role of dynamic transport in the formation of the inverted charge structure in a simulated hailstorm

The inverted charge structure formation of a hailstorm was investigated using the Advanced Weather Research and Forecasting(WRF-ARW) model coupled with electrification and discharge schemes. Different processes may be responsible for inverted charge structure in different storms and regions. A dynamical-derived mechanism of inverted charge structure formation was confirmed by the numerical model: the inverted structure was formed by strong updraft and downdraft under normal-polarity charging conditions such that the graupel charged negatively in the main charging region in the middle-upper level of the cloud. The simulation results showed the storm presented a normal charge structure before and after hail-fall; while during the hail-fall stage, it showed an inverted charge structure—negative charge region in the upper level of the cloud and a positive charge region in the middle level of the cloud—appearing at the front edge near the strong updraft in the hailstorm. The charging processes between the two particles mainly occurred at the top of the cloud, where the graupel charged negatively and ice crystals positively due to the strong updraft. When the updraft air reached the top of the storm, it would spread to the rear and front. The light ice crystals were transported backward and forward more easily. Meanwhile, the positively charged ice crystals were transported downward by the frontal subsidence, and then a positive charge region formed between the ?10 and ?25°C levels. Subsequently, a negative charge region materialized in the upper level of the cloud, and the inverted charge structure formed.     

Integrated navigation system and experiment of a low-cost and low-accuracy SINS/GPS

When SINS (strap-down inertial navigation system) is combined with GPS, the observability of the course angle is weak. Although the course angle error is improved to some extent through Kalman filtering, the course angle still assumes a divergent trend. This trend is aggravated further when using low-cost and low-accuracy SINS. In order to restrain this trend, a method that uses AHRS to substitute for SINS course angle information is put forward aimed at the hardware component characteristic of the low-cost and low-accuracy SINS including AHRS (attitude and heading reference system) and IMU (inertial measurement unit). Real static and dynamic experiments show that the method can restrain the divergent trend of the navigation system angle effectively, and the positioning accuracy is high.