共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
A simple empirical model representing the variation of shear strain throughout a simple shear zone allows us to determine the evolution of finite strain as well as the progressive shape changes of passive markers. Theoretical strain patterns (intensity and orientation of finite strain trajectories, deformed shapes of initially planar, equidimensional and non-equidimensional passive markers) compare remarkably well with patterns observed in natural and experimental zones of ductile simple shear (intensity and orientation of schistosity, shape changes of markers, foliation developed by deformation of markers).The deformed shapes of initially equidimensional and non-equidimensional passive markers is controlled by a coefficient P, the product of
- 1. (1) the ratio between marker size and shear zone thickness
- 2. (2) the shear gradient across the zone.
3.
Two types of noise afflict strain and tilt measurement. They may be categorized as “active” noise, which is due to atmospheric pressure variations, temperature variations, water-table variations and so forth; and “passive” or signal-generated noise which is a consequence of the interaction of the strain field of interest with inhomogeneities of material properties local to the measurement site.The reason why both types of noise are normally reduced by the use of long base line instruments is explained and a simple, practical long base line tiltmeter is described. 相似文献
4.
A relatively undeformed quartzite sample from the Weverton formation was experimentally deformed in plane strain at a temperature of 700° C, a confining pressure of 15 kb and a constant strain rate of 10−6/sec, in a modified Griggs apparatus. A comparison of the known experimental strain for the sample with that measured from deformed rutile needles within the quartz grains shows fairly close agreement between the two values. This confirms the validity of using the needles as intracrystalline strain markers. A comparison has been made of the microstructures and preferred orientations in the experimentally deformed sample and a naturally deformed sample of the same quartzite which has undergone the same strain. The experimentally deformed sample exhibits more inhomogeneous intragranular deformation and a “double funnel” pattern of c axes, while the naturally deformed sample exhibits more homogeneous intragranular deformation and a broad great circle girdle of c axes normal to the foliation and lineation. 相似文献
5.
Strain analysis and vorticity of flow in the Northern Sardinian Variscan Belt: Recognition of a partitioned oblique deformation event 总被引：1，自引：0，他引：1
A field example of strain partitioning has been analysed along the Nurra–Asinara transect of the NW Sardinian Variscan chain (Italy). The section in the Nurra–Asinara area is in a continuous sequence of tectono-metamorphic complexes made of low- to high-grade metamorphic rocks affected by a polyphase tectonic history. The principal fabric of the area is controlled by a D2 progressive deformation phase in which the strain is partitioned into folds and shear zone domains. The D2 stretching lineation and shear sense show a clear change from south to north. The principal meso- and micro-structures, vorticity gauges and a quantitative kinematic analysis of local strain suggest that the D2 kinematic history could be envisaged as an oblique heterogeneous deformation similar to the transpressive systems described in ancient and modern settings elsewhere. Using a simple kinematic model we also propose that both a transpressive system followed by “thrusting” or a partitioned transpressive system could be responsible for the fabric distribution and strain accumulation described in the study transect. 相似文献
6.
Evidence of a Cretaceous remagnetization in the Cameros Basin (North Spain): implications for basin geometry 总被引：1，自引：0，他引：1
The paleomagnetic results obtained in 23 sites from red beds of the northern border of the inverted Cameros Basin (northern Iberian Peninsula) prove a Cretaceous widespread remagnetization. Paleomagnetic and rock magnetic analyses indicate that the Natural remanent magnetization (NRM) is dominated by a stable and always normal polarity component carried by haematite. Two conglomerate test and five-fold test indicate that this component is a syn-tectonic overprint dated between Albian and Santonian times, most probably Albian, contemporary with a low-grade metamorphism. Remagnetization was acquired before compressional deformation and post-dates the main extensional stage of basin formation (Berriasian–Albian). Incremental fold tests provide best clustering solutions showing dispersed results and far from the expected direction. An alternative procedure to obtain fold test solution was applied considering asymmetric limb rotation. Mean directions obtained from these “asymmetric solutions” are consistent with the expected direction and yield a statistical value for significant grouping at the 95% confidence level in all fold tests performed. This reconstruction allows to determine the tilting of beds at the moment of acquisition of magnetization. These original dips were used to reconstruct the original geometry of the northern basin border, later modified during the Tertiary inversion stage. This extensional geometry can be characterised as a large-scale syn-sedimentary normal fault drag, with a minor roll-over anticline. The procedure developed in this paper should be tested in other inverted basins that also have undergone burial remagnetizations. 相似文献
7.
Ruud Weijermars 《Tectonophysics》1986,124(3-4)
The initiation of analogue studies of rock flow is stimulated by improving our knowledge of suitable model materials. Bouncing Putties and “Plasticines” are the most frequently used model materials in analogue studies of flow instabilities in deforming rocks. Polydimethyl-siloxane (PDMS) and polyborondimethylsiloxane (PBDMS), both substrates of Bouncing Putty, are introduced as convenient geological model materials. The chemistry of PDMS, PBDMS, Bouncing Putties and “Plasticines” is reviewed. A comprehensive set of instructions and graphs is provided for the manipulation of these model materials.In particular, a high viscosity PDMS produced as an intermediate compound under the code name SGM36 by Dow Corning (Great Britain) opens exciting possibilities for analogue studies of rock flow, because it is perfectly transparent. This allows continuous observation of three-dimensional strain markers during an experiment.The polymeric flow mechanisms are compared with the flow behaviour and crystal plasticity theory of rocks. The flow of natural rocks is taken to be of Reiner-Rivlin type with powers n varying between 1 and 10.Flow curves have been constructed for Bouncing Putties, Plastilinas (cf. Plasticines) and SGM36 (cf. PDMS). These original curves are supplemented with extensive data on similar materials compiled from the literature. The combined data reveal a consistent flow curve pattern for each group of model materials considered.Strain-rate softening of commercially available Bouncing Putties and “Plasticines” at low strain rates can be attributed to the solid filler concentration. The power n, which describes the departure from Newtonian flow, appears to be dependent on the angular filler volume concentration c and is governed by the preliminary equation n = 1−11c + 48c2. This finding provides a technique for manipulating liquid polymers to simulate natural rock flow with various powers of n.The (T, P) dependence of the viscosity and thermal properties of PDMS are outlined to stimulate modelling which includes natural (T, P) gradients. 相似文献
8.
Humic acids were extracted from six Paleosols (buried soils), ranging in radiocarbon ages from about 6000 to 29,000 yr. The N distribution (total N, amino acid-N, amino sugar-N, ammonia-N and “unknown” N) in each Paleosol humic acid was determined. After 6 M HCl hydrolysis, amino acid-N and ammonia-N decreased with increasing age but relative concentrations of “unknown” N increased. Aspartic acid, valine and serine were the most stable amino acids. Concentrations of amino sugars were very small, with concentrations of galactosamine exceeding those of glucosamine. The data showed that with increasing age, identifiable N components were converted to complex polymeric compounds whose identities still remain unknown. The different N-forms in HA's of geological times are valuable geochemical markers which provide useful information on the history of these soils. 相似文献
9.
John Morgan 《Tectonophysics》1994,230(3-4):181-198
A method is outlined for calculating three-dimensional finite strain in physical models of geological structures containing passive strain markers. This method makes it possible to determine the three-dimensional strain pattern in models of structures that lack any of the types of symmetry (such as that imparted by cylindrical folding) that simplified calculations in previous work. The strain markers in the new method are in the shape of stubby rectangular prisms or cubes. These form a three-dimensional grid or array occupying each of the active layers in a model (e.g., for a simple two-layer gravitationally unstable system, one grid for the overburden layer and one for the buoyant layer). Each of the grids can be described by positions of three families of “strain marker surfaces”, which are contacts between layers of strain markers.
After deformation, the model is serial-sectioned horizontally and the traces of the strain marker surfaces on the sections are digitized. The strain state is calculated at each of several hundred points arranged in a three-dimensional “output grid” extending throughout the mechanically active part of the model. An interpolation procedure is used to estimate the spacing and orientation of the strain marker surfaces in the vicinity of each of the output grid points. The following quantities are determined for each of the three families of strain marker surfaces:
1. (1) the local horizontal orientation of the strain marker surfaces;
2. (2) the local spacing of the surfaces; and
3. (3) the local inclination of the surfaces, calculated from their change in position from the serial section above, to the serial section below, the output grid point.
This information is used to generate a parallelepiped representing the strain marker geometry in the neighbourhood of the output grid point. The edges of the parallelepiped are equivalent to the coefficients of the strain matrix, from which the three principal strain magnitudes and orientations are readily derived. 相似文献
10.
The localization of plastic deformation in rock is of particular interest in geology in connection with the formation of “ductile” shear zones. It is commonly conjectured that strain softening, as evidenced by a falling stress–strain curve at constant strain rate, is likely to lead to strain localization. Yet observations in torsion tests at constant twist rate fail to show such an effect. However, a more sophisticated analysis using the theory of Fressengeas and Molinari (J. Mech. Phys. Solids 1987, 35, 185–211) for material showing strain-rate dependence of the flow stress does show that, when the boundary conditions are specified in terms of displacements, no localization is predicted in case of strain softening. In contrast, if the boundary conditions are set in terms of forces, localization can be expected for a strain softening material. This prediction needs experimental testing. 相似文献
11.
Some degree of tectonic stress within the earth originates from gravity acting upon density structures. The work performed by this “gravitational tectonics stress” must have formerly existed as gravitational potential energy contained in the stress-causing density structure.According to the elastic rebound theory (Reid, 1910), the energy of earthquakes comes from an elastic strain field built up by fairly continuous elastic deformation in the period between events. For earthquakes resulting from gravitational tectonic stress, the elastic rebound theory requires the transfer of energy from the gravitational potential of the density structures into an elastic strain field prior to the event.An alternate theory involves partial gravitational collapse of the stress-causing density structures. The earthquake energy comes directly from a net decrease in gravitational potential energy. The gravitational potential energy released at the time of the earthquake is split between the energy released by the earthquake, including work done in the fault zone and an increase in stored elastic strain energy. The stress associated with this elastic strain field should oppose further fault slip. 相似文献
12.
Khandeker Mosharraf Hossain 《Tectonophysics》1979,60(3-4):279-288
Belemnites are valuable strain markers and can be used to determine the elongation that has been suffered by the matrix in which they are situated. Experiments simulating the development of stretched belemnites have been performed to verify their deformation history. The analysis of the experimental results is used in the interpretation of field examples collected from Leytron, Valais, Switzerland. The amount of strain suffered by Leytron belemnites has been evaluated using the “least square” method and the result has been compared with that obtained by the “average elongation” method. The relationship between the final orientation of the whole specimen (θ′b) and that of the fragments (θ′f) demonstrates that the Leytron belemnites have suffered an irrotational type of deformation. 相似文献
13.
Spheres and clylinders of various rock types were embedded in a matrix of crushed rock and the combined samples were then deformed by applying uniaxial compressive loads of up to 4.5 MN. Under these conditions, large confining pressures are built up in the centre of the samples; thus the granular matrix is compressed into relatively hard rock and the objects experience flattening and stretching strains of up to 30%. The rock types used for the objects ranged from weak sandstone and shale to very strong quartzite; matrix materials were crushed adamellite, marble and a marble—salt mixture. The experiments were designed to investigate the relative deformation of the objects and the composite samples and, in particular, the effect of the ductility contrasts (or complete differences) between the objects and the matrix.Spheres and cylinders with a length/diameter ratio of unity are called “pebbles” in the paper. They experience a homogeneous flattening during compression and the ductility contrast controls the load at which yielding occurs and the relative rates at which a pebble and the surrounding matrix deform. The changes in shape of pebble and sample are related linearly and the slope of the straight line graph gives a quantitative estimate of the ductility contrast ; in this way a table of ductility contrasts for the various rock types has been constructed and the relative responses of different pebbles in a granular matrix are nicely illustrated in an artificial deformed conglomerate.Cataclasis is the dominant mode of deformation and much of the large finite strain induced into the objects occurs at surprisingly low applied loads. This suggests that deformed pebbles in natural rock need not necessarily have deformed as a result of tectonic pressures but could have changed shape during diagenesis of the host rocks. 相似文献
14.
Strain has been measured from clasts within a deformed conglomerate layer at 17 localities around an asymmetric fold in the Rundemanen Formation in the Bergen Arc System, West Norwegian Caledonides. Strain is very high and a marked gradient in strain ellipsoid shape exists. To either side of the fold, strain within the conglomerate bed is of the extreme flattening type. In the fold, especially on the lower fold closure, the strain is constrictional. Mathematical models of perturbations of flow in glacial ice have produced folds of the same geometry as this fold, with a strikingly similar pattern of finite strain. The fold geometry and strain pattern, as well as other field observations, suggest that the fold developed passively, as the result of a perturbation of flow in a shear zone, where the strain was accommodated by simple shear accompanied by extension along Y. 相似文献
15.
The finite strain of clasts (maximum aspect ratio varying from 2 to 40) in a deformed conglomerate from Dry Hill, Plymouth, Vermont, correlates inversely with the average grain size (300-150 μm) in the clast, suggesting that the operative deformation mechanism was grain-size sensitive. In a general way, the average quartz grain size appeared to be smaller in those clasts with higher volume of minerals other than quartz. Dislocation densities varied by as much as a factor of 10 from grain to grain within a clast, but the average dislocation density was relatively constant from clast to clast. If grain-size sensitivity of strength is accepted as a working hypothesis, other elements of the microstructure, such as grain flattening, grain morphology, and dislocation structure can be reconciled as happening either through a late, low strain, high stress pulse—if the current palaeostress indicators are correct to within a factor of 10 or as happening concurrently with the grain-size sensitive mechanism if the current palaeostress estimates are in error. The evidence from this study agrees with several previously published suggestions that grain-size sensitive deformation occurs in the crust for quartzose rocks with grain size of 100 to 300 μm at temperatures of 350 to 420°C. 相似文献
16.
W.E. Krumbein 《Precambrian Research》1983,20(2-4)
Several definitions of stromatolites are discussed and Kalkowsky's most important statements about stromatolites are translated from German to English. A new definition for stromatolites is proposed, namely “Stromatolites are laminated rocks, the origin of which can clearly be related to the activity of microbial communities, which by their morphology, physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure”. Unconsolidated laminated systems, clearly related to the activity of microbial communities and often called “recent stromatolites” or “living stromatolites”, are defined as “potential stromatolites”.The main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types, including iron stromatolites, are also described. 相似文献
17.
G. De Vicente R. Vegas A. Muoz-Martín J.D. Van Wees A. Casas-Sinz A. Sopea Y. Snchez-Moya A. Arche J. Lpez-Gmez A. Olaiz J. Fernndez-Lozano 《Tectonophysics》2009,470(3-4):224-242
The Iberian Chain is a wide intraplate deformation zone formed by the tectonic inversion during the Pyrenean orogeny of a Permian–Mesozoic basin developed in the eastern part of the Iberian Massif. The N–S convergence between Iberia and Eurasia from the Late Cretaceous to the Lower Miocene times produced significant intraplate deformation. The NW–SE oriented Castilian Branch of the Iberian Chain can be considered as a “key zone” where the proposed models for the Cenozoic tectonic evolution of the Iberian Chain can be tested. Structural style of basin inversion suggests mainly strike–slip displacements along previous NW–SE normal faults, developed mostly during the Mesozoic. To confirm this hypothesis, structural and basin evolution analysis, macrostructural Bouguer gravity anomaly analysis, detailed mapping and paleostress inversions have been used to prove the important role of strike slip deformation. In addition, we demonstrate that two main folding trends almost perpendicular (NE–SW to E–W and NW–SE) were simultaneously active in a wide transpressive zone. The two fold trends were generated by different mechanical behaviour, including buckling and bending under constrictive strain conditions. We propose that strain partitioning occurred with oblique compression and transpression during the Cenozoic. 相似文献
18.
19.
John Glover Stainforth 《Tectonophysics》1978,48(1-2)
In some metamorphic terrains, lineations in folded surfaces are coaxial to the folds at their hinges, but show a systematic dispersion on the limbs. A simple theoretical model is presented, based on two assumptions: (1) the layering is folded according to two idealised models, “ideal compression folding” and “ideal shear folding”, which assume that the rock material is homogeneous and the layering passive; (2) the lineation is a manifestation of the total product of the pre-folding and folding strains. In an ideal compression fold, only apparent lineations can be dispersed away from the fold-axial trend; in an ideal shear fold, however, both real and apparent lineations are dispersed in a similar way, the degree of similarity depending on the X/Y ratio of the pre-fold strain. The lineation loci of the two models are sufficiently distinct for them to be used, together with other features of the fabric, to distinguish between folds produced by dominantly vertical movements, and those produced by dominantly horizontal movements. 相似文献
20.
A.J. Vroman 《Tectonophysics》1976,30(1-2)
The offsets on the ocean floor, usually called “transform-faults” are not shear faults common in solid Hookian rocks, but reflect the viscous Newtonian properties of laminar flow at the time when the upwelling magma along the spreading center was still in a liquid state. During spreading this liquid is carried away with the walls of the spreading center. This movement creates a pattern of stream lines in the liquid which run parallel to the direction of spreading. “Transform faults” are initiated along zones where a larger rate of shear disturbs the process of solidification. Consequently the strength of the basalt after solidification will be impaired along these zones. These weak zones will fracture under the thermo-elastic stresses during the final stage of cooling.The history of the term “transform fault” is discussed and the name “spreading offset” is proposed. 相似文献