Stratigraphy and geochemistry of pillow basalts within the ophiolitic mélange of the Izmir–Ankara–Erzincan suture zone: implications for the geotectonic character of the northern branch of Neotethys     

Ergun Gökten  P. A. Floyd 《International Journal of Earth Sciences》2007,96(4):725-741

The Izmir-Ankara-Erzincan suture zone of Turkey is a broad zone of ophiolitic mélange containing numerous fragmented blocks ranging in age from Triassic to Cretaceous. Stratigraphic sequences for various mélange units are compared, together with the geochemistry of associated basaltic pillow lavas of Cretaceous age. A review of geochemical data for the pillow lavas demonstrate: (a) a dominant group of alkalic basalts with enriched incompatible elements, variable Zr/Y and Zr/Nb ratios, and (b) a range of tholeiitic basalts with slightly depleted to mildly enriched (normalized) rare earth patterns, (La/Yb)_N 0.4-3.0, and generally low Zr/Y ratios. The alkalic basalts can be chemically matched to Pacific Ocean seamounts, although the close association of red radiolarites and cherts suggests that many basalts represent the margins of such structures, rather than the main seamount edifice. Nd-Sr isotope data are typical for ocean island basalts and represent an admixture of a dominant EM-1 source and a depleted MORB-like source. Enhanced δ¹⁸O compositions are a consequence of submarine alteration and not crustal contamination. Tholeiitic compositions have affinities with both N- and E-type MORB, although most are probably representative of tholeiitic ocean islands. Overall the basalts are mainly representative of structures built on the ocean floor, rather than the oceanic crust itself, being scraped off the subducting crust and preserved in the mélange of the accretionary wedge.  相似文献   

南极普里兹湾夏季海冰边缘区内破碎海冰的分布特征          下载免费PDF全文

卢鹏  李志军  张占海  董西路 《水科学进展》2007,18(6):884-892

基于中国第21次南极考察中获得的69°00'S、76°24'E附近普里兹湾夏季海冰边缘区内破碎海冰的航拍照片,利用图像处理的方法从中提取了破碎海冰的若干几何参数,得到了海冰边缘区内随着与开阔水域距离增大,海冰面积、平均钳测直径等几何参数的变化规律。并按其尺寸的变化规律将海冰边缘区划分为边界区、过渡区和内部区三部分,其变化和波浪在冰边缘区中的衰减过程紧密相关。圆度的变化则说明海冰边缘区中海冰磨损最充分的地方是在冰间相互作用最明显的过渡区。另外,一种改进的幂函数分布和Weibull分布用来对破碎海冰尺寸的累积频率进行拟合,分布函数中各参数的变化情况很好的反映了海冰边缘区内破碎海冰的分布变化。其中,参数L_r随着与开阔水距离增加而增大(说明由于波能衰减导致可以出现的破碎海冰最大尺寸的增加);尺度参数L₀随着与开阔水距离增加而增大(反映了破碎海冰平均尺寸的增加以及由于波能的衰减而导致单位面积区域内尺寸较大的破碎海冰所占比例的增加);分布维数D随着与开阔水距离增加而减小(说明了由于波能的衰减导致破碎海冰所受约束条件的减弱);形状参数γ随着与开阔水距离增加而减小(说明了随着波能的衰减破碎海冰尺寸分布范围的增大)。  相似文献   

个旧老-卡岩体接触-凹陷带锡-铜多金属矿地质特征及成因分析   总被引：3，自引：0，他引：3  

刘明  彭省临  王力  杨斌 《矿产与地质》2007,21(4):395-403

个旧老—卡岩体接触—凹陷带是个旧矿集区最重要的锡-铜多金属成矿构造带,该带中锡、铜矿产资源十分丰富。通过对凹陷带内矿体地质特征、围岩地层含矿性、微量元素、稀土元素、稳定同位素等的研究,结合大地构造环境,结果认为,凹陷带矿体是多种成矿物质来源,经历多种地质作用、多个大地构造演化阶段的多因复成矿床,接触-凹陷带锡-铜矿体形成主要与燕山中晚期花岗岩岩浆作用有关,其次与印支期海底火山-沉积与海底（火山）喷流-热水沉积成矿作用有关。  相似文献   

裂陷盆地中的构造变换带及其石油地质意义   总被引：16，自引：0，他引：16  

漆家福 《海相油气地质》2007,12(4):43-50

构造变换带是裂陷盆地中的重要构造变形。讨论了构造变换带的含义、类型及对油气聚集的意义。裂陷盆地主干正断层之间的几何关系可以分为同向倾斜、背向倾斜和相向倾斜共3种组合方式;正断层之间的构造变换方式可以分为缓冲式、接力式、消长式、传递式和消减式等5种形式,构成15种类型的构造变换带。不同方式的断裂组合所形成的不同构造变换带类型会随着主干正断层位移的渐进增大发生相应的转变。构造变换带是有利的油气聚集区带:(1)它常常是主边界断裂带上地形高差变化较小的部位,是主要碎屑物源注入裂陷盆地的入口处,有利于发育储集层;(2)长期处于盆地内部相对高的构造部位,而且近邻生油凹陷,是油气运移指向区带;(3)它是裂陷盆地构造变形相对复杂的区带,有利于发育多种样式的油气圈闭。  相似文献   

Influence of initial density of cohesionless soil on evolution of passive earth pressure     

J. Tejchman  E. Bauer  S. F. Tantono 《Acta Geotechnica》2007,2(1):53-63

This paper focuses on the influence of the initial void ratio on the evolution of the passive earth pressure and the formation of shear zones in a dry sand body behind a retaining wall. For the numerical simulation a rigid and very rough retaining wall undergoing a horizontal translation against the backfill is considered. The essential mechanical properties of cohesionless granular soil are described with a micro-polar hypoplastic model which takes into account stresses and couple stresses, pressure dependent limit void ratios and the mean grain size as a characteristic length. Numerical investigations are carried out with an initially medium dense and initially loose sand using a homogeneous and random distribution of the initial void ratio. The geometry of calculated shear zones is discussed and compared with a corresponding laboratory model test.  相似文献   

How can the epikarst zone influence the karst aquifer hydraulic behaviour?   总被引：3，自引：0，他引：3  

Branka Trček 《Environmental Geology》2007,51(5):761-765

The role of an epikarst zone in the karst aquifer hydraulic behaviour was brought into focus in our studies referring to the catchment area of the Hubelj spring (SW Slovenia). This study points out the significance of effects of the fast preferential flow—epiflow, which is the main factor controlling solute/contaminant transport towards the aquifer saturated zone. The so-called epikarstic hypothesis is verified on the basis of the most significant research results that are supported by the most important findings from the literature.  相似文献   

Digital Image Based Approach for Three-Dimensional Mechanical Analysis of Heterogeneous Rocks   总被引：2，自引：0，他引：2  

S. Chen  Z. Q. Yue  L. G. Tham 《Rock Mechanics and Rock Engineering》2007,40(2):145-168

Summary This paper presents a digital image based approach for three-dimensional (3-D) numerical simulation and failure analysis of rocks by taking into account the actual 3-D heterogeneity. Digital image techniques are adopted to extract two-dimensional (2-D) material heterogeneity from material surface images. The 2-D image mesostructures are further extrapolated to 3-D cuboid mesostructures by assuming the material surface as a representation of the inner material heterogeneity within a very small depth. The iterative milling and scanning system is set up to generate the 3-D rock mesostructures. A Hong Kong granite specimen is used as an example to demonstrate the procedure of 3-D mesostructure establishment. The mechanical responses and failure process under the conventional Brazilian tensile test condition are examined through numerical analyses. The stress distribution, crack propagation process and failure model of heterogeneous material cases are simulated with a finite difference software. The numerical results indicate that material heterogeneity plays an important role in determining the failure behavior of rocks under external loading.  相似文献   

国内外开发区土地集约利用的途径及其启示   总被引：22，自引：0，他引：22  

班茂盛  方创琳  宋吉涛 《世界地理研究》2007,16(3):45-50

在国家宏观政策调控的背景下、开发区空间扩展与土地稀缺性矛盾目益会进一步突出。解决这一问题的出路在于提高开发区土地集约利用的程度。本文在对国内外开发区的土地集约利用手段与控制方法进行梳理的基础上，从土体利用控制的实施主体、实施程序等几个方面对国内外的情况做了比较分析，从借鉴国外开发区土地集约利用的经验和推广总结国内开发区已有的土地集约利用的经验两个角度提出了国内开发区土地进一步的集约化利用的对策建议。  相似文献   

Slab dehydration and fluid migration at the base of the upper mantle: implications for deep earthquake mechanisms     

Guillaume Richard  Marc Monnereau  Michel Rabinowicz 《Geophysical Journal International》2007,168(3):1291-1304

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Spatial variability and non-linearity of strong ground motion near a fault     

Hayrullah Karabulut  Michel Bouchon 《Geophysical Journal International》2007,170(1):262-274

We present observations of ground accelerations recorded at a small array close to the fault during the Düzce earthquake and its early aftershocks. The records show the strong spatial variability of ground acceleration over distances of only a few hundred metres. During the main shock, the peak horizontal acceleration values ranged from 0.3 to about 1.0 g at stations distant of 1.5 km only. We attribute this spatial variability to a fault zone site effect as peak ground acceleration steadily increases as the distance to the fault trace decreases. The spectral ratio between the ground motion recorded near the fault and the one outside the fault zone shows a shift of the spectral peak to lower frequencies with increasing peak accelerations. Such an observation suggests a non-linear behaviour of the fault zone due to the strong ground shaking. As much as a 45 per cent reduction in the shear wave velocity is necessary for the observed shifts. The opening of pre-existing cracks throughout the fault zone is the proposed mechanism to account for the observed shear wave reductions. The observation that elastic fault zone properties are soon recovered following episodes of large strains shows that cracks and fissures close rapidly after the strong shaking is over.  相似文献