岩质高边坡岩体变形参数及松弛带厚度研究   总被引：10，自引：0，他引：10  

聂德新 《地球科学进展》2004,19(3):472-477

预测岩质高边坡开挖后岩体变形模量的变化及松弛带厚度，是分析岩质高边坡在开挖后变形（位移）和作好防护设计的重要资料，运用波动力学关于平均应力与体积模量、岩体纵波速度与弹性模量、变形模量间的关系，通过部分实测资料及边坡应力场有限元分析的资料，分别建立了纵波速度与岩体变形模、岩体应力间的关系，研究了开挖边坡岩体变形模量的变化，预测了岩体松弛带的厚度。  相似文献   

中国大陆科学钻探主孔0～2000米流体剖面及流体地球化学研究   总被引：13，自引：6，他引：13  

罗立强孙青  詹秀春 《岩石学报》2004,20(1):185-191

地下深部流体的来源与演化的研究已成为国际地球化学领域的探索前沿和研究热点之一，中国大陆科学钻探(CCSD)为开展深部流体地球化学研究提供了珍贵的样品，构建了探索地下流体的研究平台。中给出了中国大陆科学钻探(CCSD)主孔He、Ar、N2、O2、H2、CH4、CO2流体地球化学剖面。CCSD主孔CH4浓度的变化与H2浓度的升降没有显相关性；CO2浓度的变化与钻井条件下的氧含量无显相关性；CO2浓度与CH4浓度的关系有三种情况：CO2浓度与CH4浓度不相关、CO2浓度与CH4浓度负相关、或CO2浓度与CH4浓度正相关；氦浓度的增加与CO2和CH4浓度的上升呈现一定的正相关。大气中N2、O2、Ar浓度太高，掩盖了井中N2、O2、Ar气体组分浓度变化，通常情况下N2、O2、Ar浓度变化难以作为深源气体的判据。CCSD流体与KTB流体中氧．氮关系基本一致，氧、氮线性相关(r=0.97)，表明这两种气体主要来源于大气。KTB中的CH4与乙烷、N2表现出非常强的线性关系，而在CCSD流体中CH4与乙烷、N2之间不存在线性相关性。两个地区间的流体成因、围岩相互作用机理等方面可能有所不同。在CCSD主孔中，目前已发现存在大量的CO2，及少量CO、CH4、C2H6、C3H8、C4H10和He、N2等气体。已确定300～2000米主孔出现多处来自于地下的气体异常，包括甲烷和C2～C4等烃类气体，一氧化碳与二氧化碳，稀有气体氦。根据流体各组分间相关性研究，可以判定异常中氧主要来源于大气，N2、Ar和CO2有一部分源于大气，一部分来源于地下。在流体显异常时，甲烷等烃类气体、氦、一氧化碳和绝大部分CO2来源于地下。出现显地下流体异常处，在岩石中存在裂隙、晶洞、破裂面、断层；它们作为流体迁移通道或存储空间，可能是流体存在的必要条件。某些CO2和He气异常与碳酸盐和铀矿石等围岩密切相关。  相似文献   

铜陵地区中生代中酸性侵入岩的地球化学特征及其成矿-地球动力学意义   总被引：24，自引：21，他引：24  

王元龙　王焰张旗  贾秀琴韩松 《岩石学报》2004,20(2):325-338

本文对铜陵地区晚侏罗世-早白垩世高钾钙碱性中酸性侵入岩进行了研究,发现该类岩体具有埃达克岩的地球化学特征,具体表现为:SiO2≥56％,Al2O3含量高(>15％),Na2O/K2O>1,亏损HREE,(La/Yb)N>12,负Eu异常不明显(Eu*/Eu=0.71-0.96),Sr含量高(>750μg/g),Sr/Y比值高(>38)。但是,由于岩石的K2O含量较高、εNd(t)较低和ISr值较高,又不同于典型的与板块俯冲有关的埃达克岩,而与中国东部中生代的C型埃达克岩比较类似,暗示铜陵地区的高钾钙碱性岩可能是加厚的下地壳底部基性岩部分熔融的产物。本文主要依据铜陵埃达克质岩的HREE特征,将其分为三类:第一类岩体为HREE平坦型,Yb含量较高(>1.8μg/g);第二类为HREE平坦型,Yb<1.8μg/g,(Ho/Yb)N≈1;第三类岩体HREE亏损,Yb<1.8μg/g,(Ho/Yb)N<1.2。上述三类岩石地球化学性质上的差异不太可能是分离结晶作用或地壳混染的 结果,而可能是由于幔源岩浆与下地壳物质混合的程度不同引起源区成分不同形成的。铜陵地区及中国东部埃达克质岩石可能代表了中国东部中生代时的地壳增生和加厚过程。铜陵埃达克岩主要是古老下地壳和底侵玄武岩不同比例混合部分熔融形成的,在岩浆演化过程中可能还不同程度地叠加了分离结晶作用和岩浆混合作用的影响。铜陵埃达克岩具岛弧特征,但并不表明其  相似文献   

内蒙古"宝音图隆起"的归属讨论   总被引：5，自引：0，他引：5  

沈存利  陈志勇  常忠耀 《华北地质》2004,27(1):18-23

对比研究表明，内蒙古“宝音图隆起”和狼山地区的古元古代宝音图岩群与新太古代色尔腾山岩群都是由中低级变质的各种片岩、大理岩组成，一致的岩石组合和变质相暗示二者可能是等同物而不是两个岩群。以物探资料为据的构造研究也证实，“宝音图隆起”与狼山地区之间并无槽一台级的大型断裂构造分开，二者实为统一的构造整体而不是分属槽台，只因两侧被两条近于平行的NE向断裂围限，使其总构造线方向呈NE或NNE向而与色尔腾山的构造线不同。结论认为，“宝音图隆起”仍是华北陆块的一部分，不属于内蒙古一大兴安蛉地槽褶皱系。  相似文献   

Geological controls on rock mass classification of coal from Huntly East Mine, New Zealand     

Vicki Moon  Trisha Roy 《Engineering Geology》2004,75(2):201-213

Rock Mass Rating (RMR) measurements from 65 sites within Huntly East underground coal mine are presented. All measurements are in coal, for which the dominant discontinuities are vertical cleat. Basic RMR values using two discontinuity spacings are presented: overall RMR based on the average spacing of all individual discontinuities; and cleat zone RMR based on the average spacing between zones of cleat. Cleat orientations are highly variable, but on average approximately parallel horizontal stress axes (face cleat follows maximum horizontal stress axis, butt cleat follows minimum horizontal stress axis).Contours of RMR variations throughout the mine are used to compare rock mass conditions with geological structure. It is apparent that: (1) RMR is least within downthrown fault blocks, and particularly immediately on the downthrown sides of faults, and greatest in upthrown fault blocks; and (2) RMR contours parallel horizontal stress axes within fault-bounded blocks, and bend to parallel faults at block boundaries. From similar contours for parameters contributing to RMR, the Rock Quality Designation (RQD), groundwater rating, and discontinuity condition rating create most of the observed variations in RMR. RQD is determined from the measured discontinuity frequency and hence is a measure of the degree of fracturing of the rock mass. This is interpreted as influencing the groundwater and condition parameters directly by allowing greater water ingress. Discontinuity frequency is greatest (least spacing) in the immediate vicinity of faults, and in downthrown fault blocks, generating low RMR values. Within fault blocks RQD varies little, so RMR contours align with cleat orientations.As RMR contours, faults, stress field and cleat orientation are clearly interrelated, there is unequivocally a connection between RMR and structural geology; this allows some predictive capacity in terms of ground conditions. If geological features can be accurately defined through either drilling programs or seismic surveys, then ground conditions may be predicted before panels are driven.  相似文献   

Mudstones of the Tanqua Basin, South Africa: an analysis of lateral and stratigraphic variations within mudstones, and a comparison of mudstones within and between turbidite fans     

P. O. D. Andersson  R. H. Worden† 《Sedimentology》2004,51(3):479-502

Permian deep‐water mudstones in the Tanqua Basin, South Africa, have been studied using geochemical and spectral gamma ray techniques. The mudstones occur as thick sequences between sand‐rich submarine fans, but also occur as thinner mud‐rich units within each fan. The interfan mudstones are interpreted to have accumulated during transgression and the consequent period of relatively high sea‐level, while the submarine fans and their intrafan mudstones were deposited during regression and relatively low sea‐level. Geochemical analyses revealed systematic differences between interfan and intrafan mudstones because the two types of mudstones have slightly different source lithologies. Differences between the two types of mudstone suggest that changes in relative sea‐level played a role in controlling exposure of sediment source areas. There are geochemical signals that display systematic stratigraphic trends within both interfan and intrafan mudstones. These are best explained by gradual denudation, exposure and weathering of different lithologies within a single sediment source area. Both interfan and intrafan mudstones have uniform geochemical signals along the flow direction except for the relative amount of uranium. It is most likely that the basinward increase in uranium in the mudstones is the result of reduced clastic dilution of uranium‐bearing pelagic fallout.  相似文献   

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

Maria Irene Bartolomeu Raposo  Alexandre O. Chaves  Paulo Lojkasek-Lima  Manoel Souza D'Agrella-Filho  Wilson Teixeira   《Tectonophysics》2004,378(1-2):43-63

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.  相似文献   

Geochronology and petrogenesis of the post-orogenic Cu–Ni sulfide-bearing mafic–ultramafic complexes in Jilin Province, NE China     

Fu-yuan Wu  Simon A. Wilde  Guang-liang Zhang  De-you Sun 《Journal of Asian Earth Sciences》2004,23(5):781

Northeastern (NE) China is a well-documented example of a collisional zone characterized by widespread post-orogenic granites and mafic–ultramafic complexes. Based on a study of the Hongqiling and Piaohechuan Cu–Ni sulfide-bearing mafic–ultramafic complexes in central Jilin province, we present geological, petrological, geochemical and geochronological data which indicates their post-orogenic origin.The Hongqiling complex comprises pyroxenite, olivine websterite, lherzolite, gabbro and leucogabbro. Zircon U–Pb SHRIMP analyses on a leucogabbro of the Hongqiling complex yield a weighted mean ²⁰⁶Pb–²³⁸U age of 216±5 Ma. The Piaohechuan complex is composed of gabbro, pyroxenite and dolerite, exposed as dikes. A plagioclase-bearing pyroxenite has a U–Pb zircon weighted mean ²⁰⁶Pb–²³⁸U age of 217±3 Ma, identical to that of the Hongqiling complex. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than the regional metamorphism (240 Ma) and syn-orogenic granitic magmatism (246±4 Ma). This suggests that these mafic–ultramafic complexes are post-orogenic in origin. The age data also indicated a short period of lithospheric stabilization of about 30 Ma after cessation of orogenic activity.Geochemical investigation indicates that the primary mafic magma was a lithospheric mantle-derived basalt resulting from the upwelling of asthenosphere due to lithospheric delamination during post-orogenic processes. The magmatic source was contaminated by a small amount of crustal material, and subsequent crystal fractionation resulted in the Cu–Ni mineralization.The widespread occurrence of mafic–ultramafic complexes in the Xing'an–Mongolian Orogenic Belt of NE China and in the Altay–Tianshan–Junggar Orogenic Belt of Northern Xinjiang indicates that mafic intrusions are an important magmatic suite that evolved during post-orogenic processes. Portions of this mafic magma could have underplated the lower crust, and served as the heat source for associated late-stage granitic magmas.  相似文献   

Groundwater and geotechnical aspects of deep excavations in Hong Kong     

R. A. Forth   《Engineering Geology》2004,72(3-4):253-260

Consideration of groundwater is a key element in almost every construction project. The design of deep excavations for basements or underground railway station concourses below the water table require that the water pressures are taken into account. Whilst these can be considered to be hydrostatic in soil, the decreasing permeability of rock with depth and the fact that groundwater flow is invariably along discrete fractures means that the water pressure is unlikely to be hydrostatic at depth.

Groundwater control for deep excavations can be achieved by a number of methods such as grouting, pumping or structural walls or a combination of these. For tunnelling projects grouting is extensively used, but the development of sophisticated tunnelling machines has led in many cases to the demise of compressed air as a means of groundwater control.  相似文献   

Fuzzy set approaches to classification of rock masses   总被引：6，自引：0，他引：6  

A. Aydin   《Engineering Geology》2004,74(3-4):227-245

Rock mass classification is analogous to multi-feature pattern recognition problem. The objective is to assign a rock mass to one of the pre-defined classes using a given set of criteria. This process involves a number of subjective uncertainties stemming from: (a) qualitative (linguistic) criteria; (b) sharp class boundaries; (c) fixed rating (or weight) scales; and (d) variable input reliability. Fuzzy set theory enables a soft approach to account for these uncertainties by allowing the expert to participate in this process in several ways. Hence, this study was designed to investigate the earlier fuzzy rock mass classification attempts and to devise improved methodologies to utilize the theory more accurately and efficiently. As in the earlier studies, the Rock Mass Rating (RMR) system was adopted as a reference conventional classification system because of its simple linear aggregation.

The proposed classification approach is based on the concept of partial fuzzy sets representing the variable importance or recognition power of each criterion in the universal domain of rock mass quality. The method enables one to evaluate rock mass quality using any set of criteria, and it is easy to implement. To reduce uncertainties due to project- and lithology-dependent variations, partial membership functions were formulated considering shallow (<200 m) tunneling in granitic rock masses. This facilitated a detailed expression of the variations in the classification power of each criterion along the corresponding universal domains. The binary relationship tables generated using these functions were processed not to derive a single class but rather to plot criterion contribution trends (stacked area graphs) and belief surface contours, which proved to be very satisfactory in difficult decision situations. Four input scenarios were selected to demonstrate the efficiency of the proposed approach in different situations and with reference to the earlier approaches.  相似文献