金沙江中段元古宙变质岩的Sm-Nd同位素年龄报道

金沙江中段的古老变质岩由多期变质的元古宙变质岩石单元组成。利用Sm-Nd同位素方法获得了雄松群二云母片岩全岩同位素等时线年龄1594Ma和1723Ma、2011Ma两组模式年龄。前者代表了成岩年龄,后者代表金沙江中段地层的基底年龄,这与金沙江流域乃至整个华南地壳最初形成的年龄十分相似。表明,川西、藏东地区雄松群变质岩可能属于华南地壳的组成部分。其形成时间应在早元古代或更早的时期内。     

二维地震观测系统合理性的论证方法

已知勘查区深度范围前提下,最大炮检X和道间距ΔX,不可以太大也不可以太小,施工前能够计算出它的允许值范围。     

斯通利波和渗透率的关系分析

理论和实际资料证明,在渗透性地层,低频斯通利波出现的频散和能量衰减与地层渗透率有关,因此可利用斯通利波的传播速度和能量衰减等特性来估算地层渗透率。斯通利波的能量和渗透率负相关。因为斯通利波能量代表了斯通利波的有关信息,因此可以认定斯通利波和渗透率负相关。     

Evolution of the Mesozoic Granites in the Xiong''ershan-Waifangshan Region,Western Henan Province,China,and Its Tectonic Implications

Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong'ershan-Waifangshan region in western Henan Province: high-Ba-SrⅠ-type granite emplaced in the early stage (～160 Ma),Ⅰ-type granite in the middle stage (～130 Ma) and anorogenic A-type granite in the late stage (～115 Ma). Geochemical characteristics of the high-Ba-SrⅠ-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New 40Ar/39Ar plateau ages of the early-stage Wuzhangshan granite (156.0±1.1 Ma, amphibole) and middle-stage Heyu granite (131.8±0.7 Ma, biotite) are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A-type granite, Taishanmiao pluton, was emplaced at～115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between～160 Ma and～115 Ma. The genesis of the early- and middle-stageⅠ-type granites could be linked to delamination of subducted lithosphere of the Qiniing orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qiniing -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial 87Sr/86Sr ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratons.     

Simulation of Stress Distribution around Tunnels and Interaction between Tunnels Using an Elasto–plastic Model

This article presents a computer simulation of stress distribution around tunnels and interaction between tunnels using an elasto-plastic model. A finite element method using ANSYS software has been used for the analyses of one and two tunnels at different overburden depths with different separating distances between the tunnels. The results of numerical analyses indicate that stress distribution and stress concentration around the tunnels vary with the overburden depths. It is found that the coefficients of stress concentration for elasto-plastic medium are smaller than those for elastic one by 1.9%. Furthermore, the interaction between the two tunnels rapidly decreases with the increase of separation distance between them. In addition, for quantitatively describing the interaction between the two tunnels, a critical separation distance is introduced. The critical separation distances between the two tunnels at different overburden depths are 8 m, 12 m, and 14 m respectively. This fact is very important and essential for the design of mining tunnels and to ensure safety in tunnel engineering.     

基于等效偏移距的偏移成像方法

等效偏移距偏移(EOM)成像方法将克希霍夫时间偏移的双平方根方程转化为一个单平方根方程,使输入采样在没有发生时移的情况下映射到以等效偏移距为变量的共散射点道集上,使散射能量按照双曲线规律分布。然后通过克希霍夫动校正和适用在共散射点道集上的叠加来完成偏移成像。基于等效偏移距叠前地震偏移(EOM)的基本理论,对CSP道集的抽取过程进行模拟实现,并对模型进行速度分析,实现偏移成像。     

Calculation of the Model of Coesite Inclusions and Analysis of Their Retrometamorphic Paths

The process and path of retrometamorphism of coesite have great significance to our understanding of the P-T tracks of the exhumation of ultrahigh-pressure metamorphic rocks. Most of the coesites in the eclogite from Shima, Anhui Province, the Dabie Mountains, China, are found degraded to quartz partly or wholly, with ruptures occurring in the shells, outside which include the coesite and quartz. According to the microscopic observation, the sample of coesite inclusion is composed of garnet, quartz and coesite, based on which we have built a three-shelled composite sphere model to compute the transition of coesite. Based on the crystal growth formulas and pressure conditions of the ruptures in the garnet, we have calculated the radius of the quartz sphere, which depends on temperature, and eventually drawn the different retrometamorphic paths for different retrometamorphism rates.     

Two-dimensional Numerical Modeling Research on Continent Subduction Dynamics

Continent subduction is one of the hot research problems in geoscience. New models presented here have been set up and two-dimensional numerical modeling research on the possibility of continental subduction has been made with the finite element software, ANSYS, based on documentary evidence and reasonable assumptions that the subduction of oceanic crust has occurred, the subduction of continental crust can take place and the process can be simplified to a discontinuous plane strain theory model. The modeling results show that it is completely possible for continental crust to be subducted to a depth of 120 km under certain circumstances and conditions. At the same time, the simulations of continental subduction under a single dynamical factor have also been made, including the pull force of the subducted oceanic lithosphere, the drag force connected with mantle convection and the push force of the mid-ocean ridge. These experiments show that the drag force connected with mantle convection is critical fo     

青藏高原西部降水中δ18O变化特征

根据青藏高原西部阿里地区狮泉河气象站和改则气象站取得的降水水样和降水气象资料, 分析了该区域降水中δ18O的变化特征.结果表明: 在长时间尺度上, 狮泉河和改则两站点历次降水中δ18O和气温之间都有较好的正相关, 尤其是降水中月平均δ18O与月平均降水温度之间相关性更加显著, 降水中δ18O主要受"温度效应"的影响.而在其中的某一年, 这种相关性不是很明显, 而且在降水中δ18O和降水时温度之间的相关性很好的年份, 在7月底或8月份初短期内降水中δ18O几乎都有一个突然降低的事件, 这可能与印度季风水汽输送有关.与狮泉河站相比, 在改则降水中δ18O和气温二者之间这种相关性相对较弱, 这与改则当地内陆水循环特别是强烈蒸发引起的降水有关.