Investigation of fractal distribution law for the trace number of random and grouped fractures in a geological mass

A fractal study method of the number of geological mass fractures is introduced in detail in this paper. Three main aspects of the problem were studied: (1) The random distribution of fractures in a geological mass was in good agreement with the fractal law. The size scale of the studied geological mass ranged from 2400 m to 1 mm for the length of each side, and the geological mass samples were taken from 13 coal areas in China. (2) The geological mass fractures were evidently directional and anisotropic, having originated from tectonic movement. Observation and statistics for the data from the Xuangang, Fenxi and Dongshan coal areas in Shanxi, China, demonstrated that the fracture distribution of each group, classified by the strike of the strata, still follow the fractal law, even though the fractal dimension varies to a certain extent with different strikes. (3) The sedimentary strata containing the coal seams, as a geological mass, underwent almost similar tectonic movements in their geological history. The mechanical experiments on geological mass samples from Fenxi and Jiexiu in Shanxi demonstrated that the fractal dimension of the number of fractures in the same strata is in good power function with the product of strength and elastic modulus. The larger the product of the strength of the elastic modulus is, the larger is the fractal dimension, and vice versa.     

Magnetic fabrics and rock magnetism of Proterozoic dike swarm from the southern São Francisco Craton, Minas Gerais State, Brazil

Magnetic fabric and rock magnetism studies were performed on 32 mafic dikes of a Proterozoic dike swarm from the southern São Francisco Craton (SFC; Minas Gerais State, SE Brazil). Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of remanent magnetization (ARM). The latter was performed imposing both anhysteretic (total (AAR) and partial pAAR)) and isothermal remanence magnetizations (AIRM). Partial anhysteretic remanence anisotropy was performed based on remanent coercivity spectra from a pilot specimen of each site. In most sites, AMS is dominantly carried by ferromagnetic minerals, however, in some sites, the paramagnetic contribution exceeds 70% of bulk susceptibility. Rock magnetism and thin section analysis allow classifying the dikes as non-hydrothermalized and hydrothermalized. Magnetic measurement shows that the mean magnetic susceptibility is usually lower than 5×10⁻³ (SI). Ti-poor titanomagnetites up to pure magnetite pseudo-single-domain (PSD) grain sizes carry the majority of magnetic fabrics for non-hydrothermalized dikes whereas coarse to fine grained Ti-poor titanomagnetites carry the majority of magnetic fabrics for hydrothermalized dikes.Three primary AMS fabrics are recognized which are coaxial with ARM fabric, except for two dikes, from both non-hydrothermalized and hydrothermalized dikes. Normal AMS fabric surprisingly is not dominant (31%). The parallelism between AMS, pAAR_0–30, pAAR_30–60 and pAAR_60–90 fabrics in the hydrothermalized dikes indicates that magnetic grains formed due to late-stage crystallization or to remobilization of iron oxides due to hydrothermal alteration after dike emplacement have acquired a mimetic fabric coaxial with the primary fabric given by coarse-grained early crystallized Ti-poor titanomagnetites. This fabric is interpreted as magma flow in which the analysis of K_max inclination permitted the inference that the dikes were fed by horizontal or subhorizontal fluxes (K_max<30°). Intermediate AMS fabric is the most important (41%) in the investigated swarm. It is interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike strike. ARM determinations for these sites also remained intermediate except for two dikes. In one of them, AIRM fabric resulted in normal AMS fabric while for the other AAR fabric resulted in inverse AMS fabric. A combination of AMS and ARM fabrics suggest that magmatic fabric for both dikes were overprinted by some late local event, probably related to Brasiliano orogenic processes after dike emplacement. InverseInverse AMS fabric is a minority (four dikes). ARM determinations also remained inverse suggesting a primary origin for inverse AMS fabric.     

澜沧江某电站右坝肩复杂岩体质量分类

笔者通过对澜沧江某电站右岸坝肩复杂岩体的成因进行分析,采用岩体质量指数Z并结合水利水电工程围岩分级和RMR分级等岩体分类方法对电站右岸坝肩的复杂岩体进行了综合分类。     

激光探针等离子体质谱同时测定锆石微区铀—铅年龄及微量元素

建立了一种利用激光探针等离子体质谱技术同时原位测定锆石Ｐｂ－Ｐｂ及Ｐｂ－Ｕ年龄和２５个微量元素的快速分析方法。Ｐ的检出限为１４μｇ／ｇ,Ｓｃ的检出限为３μｇ／ｇ,Ｒｂ、Ｎｂ、Ｂａ稀土元素Ｎｄ、Ｇｄ、Ｄｙ、Ｅｒ及Ｙｂ的检出限为０．１￣０．３μｇ／ｇ,Ｐｂ的检出限０．５μｇ／ｇ,其它稀土元素及Ｓｒ、ｙ、Ｈｆ、Ｔａ、Ｔｈ和Ｕ的检出限为１０￣９０ｎｇ／ｇ。方法对绝大多数微量元素的相对标准偏差为５￣１５％;     

节理网络分形在隧道超前地质预报中的应用

分形几何是20世纪70年代以来发展起来的研究非线性现象的理论和方法,这一理论的诞生为揭示隐藏于混乱复杂现象的精细结构和定量地描述它们提供了理论基础。将分形的方法引入到隧道的超前地质预报,通过岩体结构面网络的分维值来预测岩体的质量。结合工程实例可以看出,岩体结构具有良好的分形特征,其分形描述可作为评价结构岩体质量的标准之一。分形方法是评价岩体性质的一个有效的方法,具有广泛的应用前景。     

沿雅鲁藏布江缝合带东坡、日喀则等蛇绿岩体磁异常特征及其找矿标志

航空磁测△T图上清楚显示出沿雅鲁藏布江缝合带具有南北两条航磁异常,地质研究确认沿雅鲁藏布江缝合带的蛇绿岩体呈带状东西向延续近2000 km,但已知主要含铬蛇绿岩体分布于雅鲁藏布江南岸。在罗布莎和泽当地表观测到断续分布着含铬蛇绿岩体,地质研究程度较高,岩体规模不大。向西地表有出露日喀则岩体,再西段有当穷、普兰、东坡等规模巨大的岩体。航空磁测图上显示出日喀则、东坡、普兰、当穷等岩体与清晰的航磁异常对应。对上述岩体进行的地面磁测准确地确定了已知岩体与航磁异常的关系,位于雅鲁藏布江东段的罗布莎与泽当岩体属于其南部强航磁异常北缘的负异常范围内的小岩体。西部沿江含铬蛇绿岩体是断续分布的,呈短条带状或较大的三度体;地面磁测异常突出反映出地表岩体磁铁矿分布的不均匀性,在岩体边缘(包括近岩体围岩)的蛇纹石化较强,磁异常亦较强,并由此较准确地圈定出岩体范围。航磁异常反映出岩体内部有相对富积的磁性矿物和磁性体,它们可能来自深部含Fe O、Fe2O3等矿物在岩浆上涌到上地壳由于蛇纹石化而生成了Fe3O4,当温度低于480℃时形成较强的磁性。反演计算了磁性体位于3~5 km深度上,虽然蛇绿岩体及其围岩中存在的磁铁矿非直接来源于地幔物质,但含铬蛇绿岩体的岩浆物质是生成磁铁矿的主要物质贡献者。由此将航磁和地面磁测异常与大地电磁法、反射地震等方法结合可以给出岩体深部结构的地球物理特征,这有利于圈定找矿的远景地段。     

Displacement velocity effects on rock fracture shear strengths

Triaxial shear tests are performed to assess the effects of displacement velocity and confining pressure on shear strengths and dilations of tension-induced fractures and smooth saw-cut surfaces prepared in granite, sandstone and marl specimens. A polyaxial load frame is used to apply confining pressures between 1 and 18 MPa with displacement velocities ranging from 1.15 × 10⁻⁵ to 1.15 × 10⁻² mm/s. The results indicate that the shearing resistances of smooth saw-cut surfaces tend to be independent of the displacement velocity and confining pressure. Under each confinement the peak and residual shear strengths and dilation rates of rough fractures increase with displacement velocities. The sheared-off areas increase when the confining pressure increases, and the displacement rate decreases. The velocity-dependent shear strengths tend to act more under high confining pressures for the rough fractures in strong rock (granite) than for the smoother fractures in weaker rocks (sandstone and marl). An empirical criterion that explicitly incorporates the effects of shear velocity is proposed to describe the peak and residual shear strengths. The criterion fits well to the test results for the three tested rocks.     

乔治王岛菲尔德斯半岛的地温特征和岩石热物理性质

1985—1986年度和1986—1987年度在菲尔德斯半岛对地面温度进行了测量,共获得129个数据,并对带回的样品进行了岩石热导率测量,共获得210个数据。本文在分析和归纳这些数据的基础上对菲尔德斯半岛的地温特征和岩石热物理性质进行了初步探讨。     

Erosion-driven uplift of the modern Central Alps

We present a compilation of data of modern tectono-geomorphic processes in the Central European Alps which suggest that observed rock uplift is a response to climate-driven denudation. This interpretation is predominantly based on the recent quantification of basin-averaged Late Holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling. Furthermore, a GPS data-based synthesis of Adriatic microplate kinematics suggests that the Central Alps are currently not in a state of active convergence. Finally, we illustrate that the Central Alps have acted as a closed system for Holocene redistribution of sediment in which the peri-Alpine lakes have operated as a sink for the erosional products of the inner Central Alps.While various hypotheses have been put forward to explain Central Alpine rock uplift (e.g. lithospheric forcing by convergence, mantle processes, or ice melting) we show with an elastic model of lithospheric deformation, that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading. Thus, erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens. Rather, we suggest that the geomorphic response of the Alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift. Therefore, in a non-convergent orogen such as the Central European Alps, the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion.     

甘肃北山牛圈子地区志留纪骆驼圈西岩体的岩石成因及构造意义

北山牛圈子地区的骆驼圈西埃达克岩为过铝质钙碱性岩浆系列,具有高的SiO_2(57.94%)、Al_2O_3(16.66%)和低的MgO(4.32%)含量,较高的Na_2O/K_2O比值(3.13),显示富钠的特征;而在微量元素上,高Sr(589×10~(-6)~1170×10~(-6)),低Y(4.60×10~(-6)~13.90×10~(-6))和Yb(0.43×10~(-6)~1.32×10~(-6));轻重稀土分异明显(La/Dy)N=4.60~13.87、(La/Yb)N=7.17~20.58,Eu异常不明显(Eu/Eu*=0.85~1.32);富集轻稀土和大离子亲石元素,而亏损高场强元素Nb,Ta,Ti和重稀土HREE,与世界上典型的俯冲洋壳熔融形成的埃达克岩特征相似。结合区域上埃达克岩的研究成果和岀露的构造位置,以及与牛圈子蛇绿岩的关系,认为骆驼圈西埃达克岩是志留纪(U-Pb年龄为428.9 Ma)时期热的洋壳向公婆泉—东七一山早古生代活动陆缘带俯冲过程中部分熔融的产物。对该岩体的研究,为进一步研究北山造山带早古生代北山洋盆闭合和晚古生代北山洋盆重新裂开提供新的依据。