安徽庐枞矿集区大地电磁探测与电性结构分析

庐枞矿集区位于长江中下游成矿带,内赋有大型铁矿床、铜矿床及一系列中小型铅锌、铜、铜金矿床。为理解矿集区成岩成矿与深部结构的关系,通过5条大地电磁测深剖面,获得了庐枞矿集区及其邻区10km以浅的地电结构。地下电性分布清晰地反映了区域断裂位置、庐枞火山岩盆地的双层结构,指示了遭受多期构造运动的庐枞火山岩盆地外围基底出露区和大别造山带及其前陆地堑式凹陷盆地结构特征,划分了形成于不同时期、不同性质的地质构造单元,识别了火山盖层厚度和控制庐枞火山岩盆地范围的边界断裂。电性异常部位显示,与沙溪斑岩型铜矿具有成因联系的闪长岩体表现出亲造山带,可能为独立于火山岩盆地的具有不同演化路径的岩浆系统。通过3条北西—南东走向和2条北东—南西走向的剖面特征对比发现从浅至深北东-南西向构造在研究区内均占主导地位。根据一系列受断裂控制的北东-南西走向不同构造单元特征可以推演,在晚侏罗世挤压背景向早白垩纪伸展机制转变时,燕山期构造继承了印支期造山运动的前陆构造体系。     

MT在天津地热勘查中的应用及主要成果

利用大地电磁测深法(MT)反映地质体的电性差异,可以确定具有不同电性特征的地质体的空间展布。近十年来,天津在多个地热资源勘查项目中,利用MT方法确定断裂、地层并尝试圈定地热远景区,取得了一定效果。本文通过不同构造单元的MT成果,分析了这一方法在地热勘查中的适用性,从而得出:对于深大断裂、尤其是坳陷与隆起区的分界断裂在MT上有较明晰的显示;对上、下层电阻率相差较大、且分布较为稳定的地层,MT确定的地层界面较为准确;以剩余电阻率等值线圈定的地热异常区与盖层平均地热梯度等值线圈定的地热异常区相吻合的区域,通常具有比周边地区更好的地热资源条件。     

海底环境参数采集电路的硬件实现及其驱动软件设计

海底大地电磁探测与陆上同类探测的技术差别之一是其测量过程受环境因素的影响较大.为真实地获取海底岩石介质的电性模型, 在对海底大地电磁实测信号进行数据处理的同时, 需参考海底仪器的方位朝向、倾斜姿态等信息, 以便认识海底电磁场真实的矢量变化方向, 进而实现对整个测网多站位的统一资料解释.为达到这一目的, 海底大地电磁仪内部设有环境参数采集通道, 该通道对诸如方位、倾斜、温度等信息实施分时循环采集.电路包括PC104嵌入式计算机、多路选择开关、逻辑控制门阵列等硬件单元.在硬件架构搭建完成后, 开发出相配套的电路驱动软件, 实现对海底环境参数的实时记录与存储.近期的海洋试验效果显示, 所研制的电路硬件及其驱动软件已达到设计要求.      

Stress And Seismicity In The Lower Continental Crust: A Challenge To Simple Ductility And Implications For Electrical Conductivity Mechanisms

The lower crust is generally considered to be an aseismic, weak zone where fluid distribution might be governed by textural equilibrium geometries. Saline fluids below the transition from brittle to ductile rheology have been advanced as a joint explanation for deep crustal conductivity and seismic reflectivity, the depth of onset of both phenomena being apparently bounded by isotherms in the 300–450 °C temperature range. Some petrologists, meanwhile, contest that the deep crust should be devoid of extensive fluid networks. This review exposes some geophysical exceptions to the statistical norm suggested by global geophysical data compilations and presents counter-arguments that the lower crust in places may be both dry and strong, that fluids if at all present at such depths may not necessarily be connected and that fluid mobility in the lower crust may be more limited and heterogeneous than commonly assumed.Laboratory data on crustal rocks implies that the transition from brittle to ductile rheology actually occurs over a much broader range of temperatures than 300–450 °C, and the apparent association of deep crustal conductive horizons with a temperature field of 300–450 °C may be interpretable in terms of formation temperatures of graphite, rather than fluids and brittle-ductile transition rheology.High v_P/v_S ratios from a 6 km thick, seismically layered zone below the Weardale granite, NE England can be explained by underplated mafic material. They are unlikely to be explained by fluids in an area where deep crustal conductance has been shown to be relatively low, unless conventional assumptions regarding deep crustal fluid distribution are inadequate or false.Perusal of the literature reveals that lower crustal seismicity is less seldom than generally appreciated. Interpretation of earthquakes nucleating at lower crustal depths is ambiguous, but in some tectonic regimes may indicate preservation of brittle rheology to the Moho and a lower crust that is predominantly mafic and dry.A better understanding of lower crustal deformation mechanisms and history may provide better insight into deep crustal conductivity mechanisms. Recent rock mechanical experiments suggest that permeability (and thus fluid connectivity) may be decreased by ductile shearing, whereas ductile shearing may aid graphitisation at lower crustal temperatures. If the lower crust in some regions is strong, this may explain the apparent preservation of both extant- and palaeostress orientations in interpretations involving electrical anisotropy.     

改进混合蛙跳算法的CSAMT信号激电信息提取研究

从CSAMT信号中提取激电信息有利于提高频率域电磁法反演与解释的精度.目前的研究多以线性反演方法为主,存在依赖初始模型、易陷入局部极值的问题.针对CSAMT信号IP提取问题的非线性和非凸特征,本文提出了一种基于柯西分布和惯性权重的二阶段最小构造混合蛙跳反演方法来提取IP信息.该方法首先利用柯西算子取代随机算子来提高算法的全局搜索能力,并通过引入混沌震荡惯性权重来均衡进化过程中的个体经验和群体经验,保证算法后期的稳定收敛;然后通过引入第二阶段反演过程来强化极化率对观测数据的影响,同时将正则化参数引入混合蛙跳算法的适应度函数来改善反演的多解性问题;最后利用CPU并行计算加速了算法的模因组搜索过程.反演结果表明,上述方法能够较好地重构地电结构和提取激电信息,在加噪环境下具有较强的鲁棒性.相比其他非线性算法(标准混合蛙跳算法SFLA,差分进化算法DE和粒子群优化算法PSO)的反演结果,本文算法具有更强的全局搜索能力和更高的计算效率,适合对微弱的激电信息进行提取.