共查询到20条相似文献，搜索用时 46 毫秒
1.
O.Adrian Pfiffner 《Tectonophysics》1980,61(4):337-362
Strain analysis based on initially uniformly oriented elliptical particles in an oolitic limestone (Blegi oolite) was used to study the homogeneity of the state of strain on various scales, kinematics of folding and deformation mechanisms. A computer (reduced means) method for strain analysis is presented which is based on deforming a population of ellipses with shape and orientation properties of measured undeformed ooids. The strain values obtained with this method are within an accuracy of about 10% (in terms of axial ratios) and are in good agreement with the ones obtained with existing graphical methods. The state of strain is homogeneous on the scale of a thin section, handspecimen and outcrop, provided that regions around relatively strong fossils and regions of marked variations in lithology are avoided. Whole rock strains and strains as indicated by ooids alone are similar. Strain patterns in folds in limestones embedded in sandstones, shales and marl are compatible with bending accompanied simultaneously with a shortening perpendicular to the axial surface. The shortening may be attributed to the shear strains related to fold asymmetry and overthrusting. Strains on the outer arcs of a competent dolomite layer compare well with theoretical and experimental fold models; strain patterns include complex contact strains and change along the fold hinge line across a transverse fault which was active during the folding process. Strains parallel to the hinge line are more or less uniform but do not necessarily represent a plane strain state. Volume change took place during deformation. It was accomplished by pressure solution processes, the pressure solved material being partly redeposited. Pressure solution accounts for only a relatively small fraction of the bulk finite strain and was accompanied by plastic flow. Intracrystalline deformation together with grain boundary sliding and/or grain boundary migration went hand in hand with recrystallization (noteably grain growth). 相似文献
2.
A strategy to predict strain across geological structures, based on previous techniques, is modified and evaluated, and a practical application is shown. The technique, which employs cross-section restoration combined with kinematic forward modelling, consists of restoring a section, placing circular strain markers on different domains of the restoration, and forward modelling the restored section with strain markers until the present-day stage is reached. The restoration algorithm employed must be also used to forward model the structure. The ellipses in the forward modelled section allow determining the strain state of the structure and may indirectly predict orientation and distribution of minor structures such as small-scale fractures. The forward model may be frozen at different time steps (different growth stages) allowing prediction of both spatial and temporal variation of strain. The method is evaluated through its application to two stages of a clay experiment, that includes strain markers, and its geometry and deformation history are well documented, providing a strong control on the results. To demonstrate the method's potential, it is successfully applied to a depth-converted seismic profile in the Central Sumatra Basin, Indonesia. This allowed us to gain insight into the deformation undergone by rollover anticlines over listric normal faults. 相似文献
3.
基于地层力学结构的三维构造恢复及其地质意义 总被引：3，自引：0，他引：3
三维构造恢复不仅可以验证构造解释在三维空间的一致性,也可用于计算构造内部的应变状态,确定构造位移变化路径及地层力学结构对构造生长过程的影响。在Gocad三维平台上综合遥感、地震和钻井等资料,建立准噶尔盆地南缘主要勘探目的层古近系古新统—始新统紫泥泉子组(E1-2z)的面模型和霍尔果斯深层背斜的体模型,并在体模型的三维域中设置剪切模量、拉梅常数以及岩层密度,以求真实反映实际地层力学结构。在此基础上利用基于Gocad平台开发的三维构造恢复插件对两者开展恢复试验。面模型恢复结果表明,准噶尔盆地南缘山前逆冲断层上盘的恢复应变椭球长轴多呈北西方向,与该位置天山山体和山前断裂带走向斜交,这一特征印证了晚新生代以来的斜向挤压作用。但在山前第二排背斜带东西300km的范围内,恢复应变椭球长轴由霍尔果斯背斜处的近南北逐渐向东西两侧的北北东向和北西向过渡,揭示出深部隐伏断裂可能具有前陆地区典型的弧形冲断特征。体模型恢复结果表明,霍尔果斯深层背斜内部的应变状态与其所经历的运动学过程并没有显著的对应关系,恢复应变分布主要受相邻地层之间力学结构的差异控制,这就导致同一断块不同地层内部的应变状态具有不同的分布特征。在石油勘探开发领域,针对圈闭范围小尺度构造的恢复应变计算可用于构造裂缝性质、方位和分布的预测。 相似文献
4.
Detailed micro-meso to macroscopic structural analyses reveal two deformation phases in the western limb of the Hazara-Kashmir Syntaxis(HKS). Bulk top to NW shearing transformed initially symmetrical NNE-SSW trending meso to macroscopic folds from asymmetric to overturned ones without changing their trend. Sigmoidal en-echelon tension gashes developed during this deformation,that were oblique to bedding parallel worm burrows and bedding planes themselves. Strain analyses of deformed elliptical ooids using the R_f/φ method constrain the internal strain patterns of the NNE-SSW structures. The principal stretching axis(S_3) defined by deformed elliptical ooids is oriented N27°E at right angles to WNW-ESE shortening. The deformed elliptical ooids in sub-vertical bedding vertical planes contain ooids that plunge ~70° SE due to NW-directed tectonic transport. Finite strain ratios are1.45(R_(xy)) parallel to bedding plane and 1.46(R_(yz)) for the vertical plane. From these 2D strain values, we derive an oblate strain ellipsoidal in 3D using the Flinn and Hsu/Nadai techniques. Strains calculated from deformed elliptical ooids average-18.10% parallel to bedding and-18.47% in the vertical plane.However, a balanced cross-section through the study area indicates a minimum of~-28% shortening.Consequently, regional shortening was only partially accommodated by internal deformation. 相似文献
5.
Some Distinctions Between Self-Similar and Self-Affine Estimates of Fractal Dimension with Case History 总被引：1，自引：0，他引：1
Thomas H. Wilson 《Mathematical Geology》2000,32(3):319-335
Compass, power-spectral, and roughness-length estimates of fractal dimension are widely used to evaluate the fractal characteristics of geological and geophysical variables. These techniques reveal self-similar or self-affine fractal characteristics and are uniquely suited for certain analysis. Compass measurements establish the self-similarity of profile and can be used to classify profiles based on variations of profile length with scale. Power spectral and roughness-length methods provide scale-invariant self-affine measures of relief variation and are useful in the classification of profiles based on relative variation of profile relief with scale. Profile magnification can be employed to reduce differences between the compass and power-spectral dimensions; however, the process of magnification invalidates estimates of profile length or shortening made from the results. The power-spectral estimate of fractal dimension is invariant to magnification, but is generally subject to significant error from edge effects and nonstationarity. The roughness-length estimate is also invariant to magnification and in addition is less sensitive to edge effects and nonstationarity. Analysis of structural cross sections using these methods highlight differences between self-similar and self-affine evaluations. Shortening estimates can be made from the compass walk analysis that includes shortening contributions from predicted small-scale structure. Roughness-length analysis reveals systematic structural changes that, however, cannot be easily related to strain. Power-spectral analysis failed to extract useful structural information from the sections. 相似文献
6.
We apply multiple balancing/restoration methods to three examples of fault-bend folds exhibiting increasing levels of complexity and uncertainty. Three methods (the Chamberlin depth-to-detachment calculation, direct measurement of fault displacement, and flexural-slip restoration/balancing) assume that bed lengths and thicknesses (BLT) remain constant during deformation. The area-depth-strain (ADS) method allows bed lengths and thicknesses to vary during deformation. For a kinematic model, the agreement among methods is exact to within measurement error. For an experimental sand model, the disagreement among methods is substantial. The ADS relationship shows that the sand model has significant layer-parallel shortening and an area increase of ∼4%. A previously published interpretation of a seismically imaged fault-bend fold from the Rosario oil field, Venezuela, is nearly line-length balanced, but the ADS relationship indicates small, but significant, anomalies, including an area deficit for the deeper stratigraphic levels. A revised interpretation with a more internally consistent ADS relationship suggests that much of the footwall uplift is real and not a velocity pull-up. Our comparisons of the results of the various balancing/restoration techniques show the resolving power of the ADS method to detect sub-resolution changes in bed lengths and thicknesses and to identify footwall structures overlooked by the constant BLT methods. 相似文献
7.
Deformation studies require that geological bodies are kinematically moved along faults. Fault-parallel flow is one of a small number of kinematic restoration algorithms developed for this purpose. This scale-independent method describes how material nodes are displaced parallel to the fault plane, in the direction of fault movement. The one-dimensional strain of linear objects and two-dimensional strain of bodies within the hanging-wall during the restoration is shown for all cutoff angles and all angles of fault bends. A line moving over a fault bend is either shortened or extended depending on its initial orientation. However, the elongation of the line is significantly different under shortening and extension, with respect to the fault bend angle. The geometries of compressional fault systems, in which faults change angle by about 20 to 40°, generate low values of elongation. Modeling of extensional faults, which typically have steeper dips (60 to 80°) and therefore have tighter fault bends, causes high, unnatural values of elongation. The calculated strain ellipse ratios are directly proportional to the fault bend angle, corroborating the one-dimensional results. The fault-parallel flow method should be used primarily to kinematically restore and forward-model compressional faults, and other faults where the fault bend angles do not exceed 40°. 相似文献
8.
This paper considers the basic principles of the strain analysis method based on the analysis of antitaxial regeneration fibrous fringes around linear rigid inclusions in a low-viscosity rock matrix. This method has been developed for pressure shadows composed of fibrous minerals, whose orientation is controlled by the major elongation direction rather than the orientation of rigid inclusions. This approach is applicable only for rocks exposed to uniform coaxial straining. The strain ellipse is calculated in two ways: for three variably oriented strain markers, it is calculated using Mohr’s circles, and for numerous strain markers by average body ellipse. The strain ellipsoid is calculated using the parameters of a few strain ellipses calculated with three and more non-parallel planes. This paper provides the data on the method testing in reference sites of Dora–Pil’ ore field in the Upper Indigirka district and Vangash area in the Yenisei Range. Regeneration fibrous fringes around fragments of fern fossils and linear rutile metacrystals were used as markers. The results of strain analysis obtained for the reference sites in the Upper Indigirka district made it possible to describe the signs of variable strain stages of developing strike-slip zones making up the Adycha–Taryn Fault Zone. Sublatitudinal ore-bearing strike-slip zones are characterized by a subvertical orientation of the elongation axes X of elongated strain ellipsoids, which are subperpendicular to quartz–carbonate veins and slope kink zones. NW-trending strike-slip zones are characterized by subhorizontal orientation of the Z shortening axes of flattened strain ellipsoids, which are subparallel to the normals of quartz–carbonate veins and veinlets. The results of strain analysis obtained for reference sites in the Vangash area made it possible to describe the thrust strain environment following the metamorphism stage and to reveal specific features in the formation of the strain textures of ore-bearing rocks based on their rheological properties. 相似文献
9.
Conventional cross-section balancing techniques based on layer length measuring can be applied only for foreland structures. To analyse complicated hinterland structure with numerous small-scale folds, this balancing technique requires the reliable and detailed tracing of the morphology of any layer throughout the cross-section, which is unattainable. We present a special kinematic method of balancing cross sections based “on the geometry of the folded domain” which enables the structural restoration of hinterland regions. We apply the method to restore the detailed structural section along the Shilbilisaj River, having a length of 26 km. We divided this section into 40–60 so-called “domains” each including 2–7 folds. Our method uses the fold's morphology to determine the strain ellipsoid, which describes the deformation of each domain and is used to restore its pre-folded state. By combining the pre-folded states of the domains, we reconstruct the entire profile, and calculate shortening values as K = L0/L1 (initial to final length). The overall shortening value for the profile is 4.49, incrementally varying along the section from 3.79 to 5.53. The comparable results of two independently performed reconstructions emphasize the reliability of the applied balancing method. 相似文献
10.
本文采用褶皱等倾线法，砾石三维应变和S－C夹角等应变测量方法，对富蕴地区阿尔泰造山带一个50km的剖面进行了系统的有限应变测算，得出其顺层缩短和剪应变剖面图，测量结果表明，该剖面褶皱压扁的顺层缩短最高达78％，断层处的剪应变（γ）最大可达8左右，三维应变分析和Finn图解表明该区应变主要为平面应变，断层活动为简单剪切，利用分段积分和正态曲线恢复方法对剖面的缩短和剪切进行应变恢复，结果表明该剖面由原宽为267.2km的原始剖面经缩短和剪切而形成。 相似文献
11.
Complexity and scale in geomorphology: Statistical self-similarity vs. characteristic scales 总被引：3，自引：0，他引：3
Robert Andrle 《Mathematical Geology》1996,28(3):275-293
Two models of the relationship between complexity and scale of geomorphic lines are compared, one based on statistical self-similarity (in which complexity is invariant for some range of scale), and the other on the concept of characteristic scales (in which complexity changes continuously with scale). Two corresponding techniques are used in the comparison, fractal analysis utilizing the divider method, and an angle measure technique. These techniques are applied to three types of coastlines: fiord, volcanic, and tectonic, in order to ascertain which model, statistical self-similarity or characteristic scales, is more useful in understanding variations in coastline complexity for scale. Apparently linear log-log plots of number of steps against steplength produced by fractal analysis display slight but significant curvature. Upon closer examination, it is determined that using fractal dimension to compare even the same types of features is unreliable because of the dependency of fractal dimension on scale of measurement, even if the same steplengths are used throughout the study. These results are corroborated by the use of the angle measure technique, a method based on measuring angles between points along a digitized line. It is concluded that the coastlines examined display no evidence of statistical self-similarity and that the characteristic scales model is more useful in investigating complexity and scale in geomorphology. 相似文献
12.
We examine the development of the Yanjinggou anticline, a fault-propagation-fold in the southern Longmen Shan, through an integrated study of structural geometry, strain, and paleomagnetism. The 3-D structural and strain restoration models generated in our analysis reveal that the NE-trending Yanjinggou fold has a curved map trace that is convex to the southeast. The fold has three distinct regions characterized by different strain patterns: contraction in the core of the fold, extension in the outer arc, and a forelimb with distributed shear. To further understand the kinematics of the Yanjinggou anticline, we performed paleomagnetic analysis on 184 oriented samples collected across the structure. Anisotropy of magnetic susceptibility (AMS) measurements and stepwise thermal demagnetization were conducted. A strike test was applied to the high temperature component (HTC) in order to identify rotation around the arc. The result indicates that the Yanjinggou anticline is a progressive arc, with a minor initial curvature and a dominant secondary curvature related to vertical-axis rotation synchronous with thrusting. The primary curvature and initial development of the structure correlates with the growth of the southern Longmen Shan in Late Miocene. The secondary curvature correlates with displacement extending since Late Pleistocene toward the southeast into the central basin along the detachments that underlie the structure. Lateral gradients in displacement along this underlying detachment provide a mechanism for producing the vertical rotation of the anticline. AMS results and historical earthquake analysis imply that the fault-propagation fold, along with other NE trending structures in the southern Sichuan basin, are tectonically active and accommodate east-west crustal shortening in the basin. By integrating 3-D structural and strain restoration modeling with systematic AMS and paleomagnetic methods using statistical analysis, we closely constrain how the Yanjinggou anticline developed, and provide insights into the formation of fault-related folds with curved shapes in map view, which are common in other fold-and-thrust belts around the world. 相似文献
13.
Specimens of fine grained micritic limestone were deformed in plane strain geometry in pure shear, a combination of simple and pure shear, and in simple shear. Temperatures were 400° C and 500° C, confining pressure was 100 MPa. In the experiments with a simple shear component strain is concentrated and approximately homogeneous in a 2–3 mm wide shear zone. Shear displacement is documented by marker lines and circles. Shear strain γ varies between 0.84 and 1.56. Strain is recorded by flattening of individual grains, defining a foliation normal to the axis of principal finite shortening ε 1. No twinning is observed on a macroscopic scale. X-ray and neutron diffraction techniques were used to characterize texture before and after deformation. All specimens display strong preferred orientation as documented by 0006, 10¯14 and 11¯220 pole-figures, c axes pole-figures display three maxima in the ε1–ε3 plane. If the axes of the strain ellipsoids are used as a coordinate system textures in pure and simple shear are similar but there is considerable monoclinic distortion in simple shear which is attributed to the noncoaxial strain path. 相似文献
14.
R.G. Park 《Precambrian Research》1981,14(1):31-47
The later Archaean history of the granite-greenstone terrain of the western Superior Province in Manitoba was marked by the development of numerous shear zones with varying orientation and sense of movement. Data are presented on the orientation, width and displacement of 15 shear zones in a 61,000 km2 area east of Lake Winnipeg. By making simplifying assumptions, estimates are made of the orientation of the maximum compressive stress (N-S) and the bulk shortening strain caused by the shear zone displacements (39–45%).The estimates of shear zone displacement strain are compared with estimates of bulk strain obtained by analysing the granite-greenstone shape pattern over a large area of the western Superior Province, again making simplifying assumptions. As expected, the contribution of the more ductile greenstones to the bulk strain is proportionately greater. A value of around 40% is indicated for the bulk shortening strain.Estimates of mean shear strain obtained both from shear zone displacement/width measurements and from strain profiles show a wide range in values from around 10 in some narrow zones to around 1 in very wide zones. 相似文献
15.
V.K. Gairola 《Tectonophysics》1977,41(4):291-319
Experiments have been carried out to study the orientation and values of the three principal extensions during folding, and to investigate the nature of the deformation paths of the strain ellipsoids at the fold hinges. Single layers embedded in a matrix were deformed by plane strain pure shear with the layers obliquely inclined to the axes of the bulk strain. The strains on the outer and inner arcs of the fold hinges were measured by means of grids on the layer surfaces. The orientation and values of three principal strains during folding depend on the layer orientation and the degree of deformation, and may be different on the outer and the inner arcs. The deformation paths in the outer arc are generally in the constriction field and those in the inner arc lie in the flattening field. The deformation paths have been computed by analyzing the manner by which components of layer shortening, tangential longitudinal strain and elongation parallel to the fold-hinge line combine to give the finite strain. 相似文献
16.
《Journal of Structural Geology》2001,23(2-3):379-392
Fault-slip data are used to reconstruct varying tectonic regimes associated with transverse fold development along the eastern and southern margins of the Jaca basin, southern Pyrenees, Spain. The Spanish Pyrenean foreland consists of thrust sheets and leading-edge décollement folds which developed within piggyback basins. Guara Formation limestones on the margins of the Jaca basin were deposited synchronously with deformation and are exposed in the External Sierra. Within the transverse folds, principal shortening axes determined from P and T dihedra plots of fault-slip data show a shift from steep shortening in stratigraphically older beds to NNE–SSW horizontal shortening in younger beds. Older strata are characterized by extensional faults interpreted to result from halotectonic (salt tectonics) deformation, whereas younger strata are characterized by contraction and strike-slip faults interpreted to result from thrust sheet emplacement. The interpretation of the timing for the shortening axes in the younger strata is supported by the observation that these axes are parallel to shortening axes determined from finite strain analysis, calcite twins, and regional thrusting directions determined from fault-related folds and slickenlines. This study shows that fault population analysis in syntectonic strata provides an opportunity to constrain kinematic evolution during orogeny. 相似文献
17.
Zoltán Gribovszki 《Hydrogeology Journal》2018,26(3):869-880
Methods that use diurnal groundwater-level fluctuations are commonly used for shallow water-table environments to estimate evapotranspiration (ET) and recharge. The key element needed to obtain reliable estimates is the specific yield (Sy), a soil-water storage parameter that depends on unsaturated soil-moisture and water-table fluxes, among others. Soil-moisture profile measurement down to the water table, along with water-table-depth measurements, can provide a good opportunity to calculate Sy values even on a sub-daily scale. These values were compared with Sy estimates derived by traditional techniques, and it was found that slug-test-based Sy values gave the most similar results in a sandy soil environment. Therefore, slug-test methods, which are relatively cheap and require little time, were most suited to estimate Sy using diurnal fluctuations. The reason for this is that the timeframe of the slug-test measurement is very similar to the dynamic of the diurnal signal. The dynamic characteristic of Sy was also analyzed on a sub-daily scale (depending mostly on the speed of drainage from the soil profile) and a remarkable difference was found in Sy with respect to the rate of change of the water table. When comparing constant and sub-daily (dynamic) Sy values for ET estimation, the sub-daily Sy application yielded higher correlation, but only a slightly smaller deviation from the control ET method, compared with the usage of constant Sy. 相似文献
18.
Gregory H. Roder 《Tectonophysics》1977,43(3-4)
Two methods are presented whereby finite-strain data may be determined from naturally occurring irregular strain markers (polygons) which are of unknown pre-deformation shape and distribution, without assumptions as to the orientation of the finite-strain ellipse. The first method describes “construction” of ellipses within the polygons, these ellipses providing the basis for analysis by already developed techniques. The second method is a simple extension of Wellman's method, which graphically establishes a strain ellipse from angle and line data. 相似文献
19.
Deformed conglomerates and ooidal/oncoidal packstones are commonly used to evaluate finite strain in deformed sedimentary successions. In order to obtain a correct estimate of finite strain, it is necessary to consider not only the different behaviour of matrix and objects, but also object concentration. The analysis of two-component rocks characterised by high values of packing commonly results in a substantial underestimate of bulk strain and of viscosity contrast between objects and matrix. In this study, the effects of the volumetric fraction of competent inclusions on both object and bulk measured finite strain, as well as on apparent viscosity contrast, have been investigated in naturally deformed packstones characterised by variable object concentration on the scale of the hand specimen (and hence for homogenous viscosity contrast). Object finite strain has been obtained by Rf/ analysis, whereas the Fry method provides a measure of whole-rock strain that is also a function of inclusion concentration. Therefore, the finite strain measured by the Fry method is better termed effective bulk strain. In order to investigate the role of object concentration, this parameter has been plotted against object and effective bulk strain, and also against viscosity contrast. These diagrams show that: (i) for high values of packing, measured object and effective bulk strain show values that are significantly lower with respect to the calculated maximum value (that would result in the ideal case of no particle interaction and represents therefore the real bulk strain of the samples); (ii) the viscosity contrast shows lower values with respect to the calculated maximum one (that is equal for the three principal sections of the finite strain ellipsoid), and as packing reaches the maximum value, the viscosity contrast approaches a unit value. Empirical equations have also been found that link object concentration with both object and effective bulk finite strain. 相似文献
20.