Variations of the alpine precipitation from an ice core record of the Laohugou glacier basin during 1960-2006 in western Qilian Mountains,China

The net accumulation record of ice core is one of the most reliable indicators for reconstructing precipitation changes in high mountains. A 20.12 m ice core was drilled in 2006 from the accumulation zone of Laohugou Glacier No.12 in the northeastern Tibetan Plateau, China. We obtained the precipitation from the ice core net accumulation during 1960-2006, and found out the relationship between Laohugou ice core record and other data from surrounding sites of the northeastern Tibetan Plateau. Results showed that during 1960-2006, the precipitation in the high mountains showed firstly an increasing trend, while during 1980 to 2006 it showed an obvious decreasing trend. Reconstructed precipitation change in the Laohugou glacier basin was consistent with the measured data from the nearby weather stations in the lower mountain of Subei, and the correlation coefficient was 0.619 (P<0.001). However, the precipitation in the high mountain was about 3 times more than that of the lower mountain. The precipitation in Laohugou Glacier No.12 of the western Qilian Mountains corresponded well to the net accumulation of Dunde ice core during the same period, tree-ring reconstructed precipitation, the measured data of multiple meteorological stations in the northeastern Tibetan Plateau, and also the changes of adjacent PDSI drought index. Precipitation changes of the Laohugou glacier basin and other sites of the northeastern Tibetan Plateau had significantly positive correlation with ENSO, which implied that the regional alpine precipitation change was very likely to be influenced by ENSO.     

上海地区单桩水平承载力的若干影响因素研究

结合上海软土地区12个场地57根单桩水平静载荷试验,研究建筑桩基单桩在水平荷载作用下的受力特点。根据试验实测数据,探讨不同桩径、不同试验加载方法及灌芯对预应力空心桩受力性状影响等因素,认为建筑工程中,可选择桩径较大或者采用在桩顶一定范围内扩大桩径的做法进行单桩水平承载力优化设计,试验加载方式建议可采用单向单循环恒速水平加载法,预应力空心桩顶部灌芯可作为水平承载力的安全储备,为软土地区类似工程的单桩水平承载力的设计和理论研究提供参考。     

日本海沟俯冲带热结构与深源地震

本文利用有限差分方法,计算了全地幔对流模式和双层地幔对流模式下日本海沟俯冲带热结构、浮力及P波速度异常分布,基于亚稳态橄榄石相变模型推测亚稳态橄榄石的存在范围,同时分析了热传导系数、热膨胀系数和热源对俯冲带热结构的影响,以及俯冲带所受浮力与俯冲带形态的关系.结果表明,双层地幔对流模式下模拟的P波速度异常分布与层析成像结果更为相符,也与深源地震的分布有较好的相关性.板块内部亚稳态橄榄石的存在范围随热传导系数和热膨胀系数的减小而增大,同时忽略相变潜热和剪切生热的影响也会造成模型所预测的亚稳态橄榄石范围偏大.俯冲带所受负浮力在400 km深度附近达到最大值,亚稳态橄榄石的存在使负浮力逐渐减小,甚至在板块内部产生正浮力,不利于俯冲带穿透660 km相变界面.     

Formation of elongated granite–migmatite domes as isostatic accommodation structures in collisional orogens

The mid-Carboniferous Pelhřimov core complex, Bohemian Massif, is a crustal-scale elongated granite–migmatite dome interpreted to have formed by gravity-driven diapiric upwelling of the metapelitic middle crust. The vertical diapiric flow is evidenced by outward-dipping foliation and lineation patterns, deformation coeval with the widespread presence of melt, rapid exhumation of the dome center from depths corresponding to pressure of about 0.6 GPa to shallow levels (pressure less than 0.2 GPa) within 2 M.y., and kinematic indicators of downward return flow of the mantling rocks. As compared to common diapirs, however, the Pelhřimov complex exhibits a more complicated inferred strain pattern with two perpendicular, irregularly alternating directions of horizontal extension in what is interpreted as the diapir head. Comparison of structural data from migmatites with anisotropy of magnetic susceptibility (AMS) data in granites also reveals that only final increments of strain are recorded in the granites. The map dimensions and gravity image of the complex suggest that the diapiric upwelling affected a large portion of the orogen's interior between two microplates brought together during continental collision. The northwesterly microplate (the upper-crustal Teplá–Barrandian unit) collapsed vertically as an ‘elevator’ at around 346–337 Ma whereas the easterly microplate (Brunia) was underthrust beneath the Moldanubian rocks during ∼346–330 Ma (the indentor). It is suggested that these microplates then acted as cold and rigid margins localizing mid-crustal diapirism and associated voluminous S-type granite plutons inbetween, parallel to the edge of the Brunia indentor.We conclude that bringing together soft metapelitic middle crust with two rigid lithospheric blocks during collision resulted in significant lateral temperature and strength variations across the orogen's interior. A general conclusion from these inferences is that granite–migmatite domes delineating margins of collided microplates may form as crustal-scale structures accommodating late-orogenic isostatic reequilibration.     

天津局地暴雨特征及落区预报分析

利用常规观测资料分析2009-2011年天津地区33次局地暴雨天气过程的影响系统。对局地暴雨天气发生前的大气环境物理参数进行统计,对比不同影响系统下预报着眼点的差异。结果表明：天津局地暴雨主要发生在蒙古冷涡、东北冷涡、高空槽前以及高空槽后四种天气系统的影响下。蒙古冷涡系统下应以整层良好的水汽和涡旋系统东南象限深厚的辐合上升运动为着眼点;而东北冷涡系统下则需关注低层水汽条件充沛和中层强烈的辐合抬升;高空槽系统下在动力、水汽以及能量条件配合较为均衡;而槽后型系统影响下若发生局地暴雨,各种强对流参数特征则最为显著。在此基础上,通过典型局地暴雨过程对强降水落区进行诊断表明,天津构造加密探空由于充分考虑了近地面的温湿风特征,计算所得的可降水量、对流有效位能以及地面至3km高度的垂直风切变对局地暴雨落区具有良好的指示性。同时,个例研究也表明TJ-WRF对局地暴雨天气过程有较好的预报能力,综合应用模式物理量结果能较好地预报局地暴雨落区。     

黔东地区变质核杂岩构造及其控矿作用

黔东地区的变质核杂岩构造其变质核杂岩为中元古界四堡群、梵净山群变质基底,其主滑脱面发育于新元古界底部的甲路组,同时在下江群、板溪群中出现一系列次级滑脱面,在其上的早古生代地层中则发育伸展剥离正断层系统。该类型构造形成于加里东期末,是该区加里东造山期后隆升背景的产物。变质核杂岩构造与该地区的金、铜、铅、锌、锑及汞等矿产关系十分密切,它们分别受控于主滑脱带、次级滑脱带及伸展剥离正断层系统,且在剖面上矿物组合、成矿温度出现有规律变化,反映出该地区金及多金属矿产是受控于变质核杂岩构造的一个完整的、相互有机联系的成矿系统。     

一次蒙古冷涡影响下宁夏强对流天气分析

2004年6月14、15日连续2 d宁夏大部地区出现了强雷阵雨天气,引黄灌区局部地区遭受冰雹袭击。利用常规气象资料、多普勒雷达产品等资料,对此次过程进行了天气学分析,分析表明这是一次典型的蒙古冷涡旋转东移南压造成的宁夏连续性强对流天气过程。并根据一般性雷雨与伴有冰雹的强雷雨天气发生时雷达回波的差异,统计得到宁夏发生强对流性天气的监测预警指标,同时利用宁夏中尺度区域模式MM5预报产品对其相关物理量进行了模拟分析,得到了有价值的结果。     

上地幔密度异常驱动小尺度对流及实验模型

建立了由密度异常驱动上地幔小尺度对流的数学 物理模型, 发展了利用地震层析成像数据反演上地幔小尺度对流的基本理论和方法. 该模型建立在三维直角坐标系框架上, 假设地震层析成像所显示的地震波速度异常对应于上地幔物质密度异常, 而该密度异常反映了上地幔小尺度热对流系统的温度异常场. 模型首先将地震层析成像确定的地震波速度异常转换为密度异常, 并视其为对流的驱动力; 进而利用三维傅立叶变换, 在波数域内, 在给定的边界条件下, 求解控制流体行为的运动方程和连续性方程, 最后求得对流的流场. 为检验本研究提出的理论和方法的有效性, 本文使用了两个简单的实验模型: 热体和冷体模型; 俯冲断离( break off)板片模型, 计算了其驱动的地幔流场. 结果表明, 本文提供的理论和方法, 可以直接应用于与区域岩石层构造动力学相关的上地幔小尺度对流的研究.      

渭河下游咸阳-草滩段河谷沉积对构造活动的响应

渭河下游咸阳-草滩段河道位于西安凹陷向临潼隆起的过渡区,发育河漫滩和T₁～T₃阶地,渭河断裂隐伏于河道北岸。文章对渭河北岸河谷地貌和地层剖面进行了观测和年代学样品的测试,并对跨渭河断裂的系列钻探中的2个深150m的钻孔岩芯进行了年代学样品测试和地层对比。河谷区地层年代测定表明,渭河北岸在距今约10万年前为风成黄土堆积环境,大致在2.5万年以来开始了最新一期的河道沉积。钻孔岩芯揭露的多个黄土-河流冲积的沉积旋回显示第四纪时期渭河河道经历了多次的南北向摆动。受临潼隆起的影响,咸阳-草滩段晚第四纪河谷沉积自西向东厚度明显减薄。通过对渭河断裂两侧钻孔柱状图的对比,认为渭河断裂0.04～0.05m/ka垂向差异运动速率低于河流0.15～0.24m/ka沉积速率,是渭河断裂隐伏于河谷中的原因。     

中南半岛对流对南海夏季风建立过程的影响

利用RegCM2模式进行数值试验,得到中南半岛对流对北半球副高带断裂、进而对孟加拉湾对流建立具有重要影响,而孟加拉湾对流建立后激发的Rossby波列又是南海夏季风建立的主要因子之一.进一步分析中南半岛对流、副高带断裂及南海夏季风建立的年际变化,得到中南半岛对流的强弱(活跃的早晚)与副高带在孟加拉湾北部断裂及南海夏季风爆发的早晚有密切关系.它们还与海温异常及纬圈环流的变化相联系:当赤道中东太平洋海温偏暖(冷)时,Walker环流偏弱(强),中南半岛对流偏弱(强),副高带断裂偏晚(早),南海夏季风建立偏迟(早).