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金矿赋存于挤压——滑脱构造破碎带中。成矿受构造、地层（岩性）、地球化学条件和围岩蚀变等条件控制。该区具有较大的找金潜力。 相似文献
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Crack-related fabric analyses were carried out in terms of crack tensors using Inada granite deformed inelastically in a triaxial vessel up to post-failure, focusing on the fabric changes during brittle failure. Complementarily, numerical simulation tests were conducted to determine the representative volume element (RVE) required for crack surveying. Numerical simulation tests show that the window size for crack surveying should be at least six times the mean trace length in order to obtain a statistically meaningful crack tensor. A larger window is needed to estimate the distribution of crack radii. In quartz, cracks grow preferentially parallel to the major loading axis. Crack tensors in quartz can provide a measure of damage reflecting inelastic deformation under differential stress in past geological events. During the first stage of inelastic deformation, the number density of cracks decreases with a rather sharp increase in crack diameters. This happens because pre-existing cracks in intact rock join together to make longer cracks. However, the density remains almost constant during the second stage of loading from 90% to 100% of the peak stress. The crack diameter gradually increases due to the stable propagation of cracks. When granite is further deformed beyond the peak stress, the number density decreases again while sharp increases in crack diameters appear as a result of the forking and coalescence of cracks. It is also suggested that load-normal grain boundary cracks are generated as a result of the rolling and sliding of disintegrated blocks in the post-failure stage. 相似文献
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P. Beneduce V. Festa R. Francioso M. Schiattarella M. Tropeano 《Physics and Chemistry of the Earth》2004,29(10):717-724
The Matera Horst (“Murgia materana”) is included in the Apulian plateau, basically formed by Mesozoic shallow-water carbonates. The zone is located in a present-day temperate belt and form a flat-topped morphostructural large element inside the foreland area of the southern Apennines. This horst is bordered by high-angle faults and surrounded by downthrown blocks covered by Plio-Quaternary marine and alluvial sediments. The structural high experienced several morphological cycles from Miocene to Quaternary. In particular, three evolutionary stages can be recognized at least. The first stage is currently represented by relics of a flat erosional landscape at the top of the relieves. The second one is testified by gentle slopes with wide glacis at the foothills, locally covered by coarse waste deposits. During the third stage a series of marine terraces formed and a drainage system developed creating both bland valleys and well-defined channels and gorges. The latter streams deeply carve the Cretaceous limestone of the Matera Horst for they represent the morphological response to the tectonic uplift of the area and clearly post-date the former features. Since the fluvial net took place on Pleistocene covers, later widely eroded, it is possible to conclude that the major part of the Matera Horst drainage system represents a good example of superimposition. However, low order streams and segments of major rivers appear to be structurally controlled, as suggested by comparison with the fracture system. Further, also open synclines and gently steeped flexures may locally exert a driving control on minor streams. These apparently conflicting genetic hypotheses can be explained by the role of exhumation of inherited structures of the bedrock in add to a constant interplay between tectonics, erosion and drainage evolution during Quaternary times. 相似文献
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Theocharis Baxevanis Euripides Papamichos Olav Flornes Idar Larsen 《Acta Geotechnica》2006,1(2):123-135
The mechanical behavior and permeability of the Tuffeau de Maastricht calcarenite were studied. Compactions bands were found to form in the “transitional” regime between brittle faulting and cataclastic flow. In order to predict the formation of compaction bands, bifurcation analysis was applied on a model developed by Lade and Kim. The numerical results proved to be in good agreement with the experimental ones where the localization point was identified to be the onset of shear-enhanced compaction (a threshold in differential stress after which significant reduction of porosity is induced). Before the onset of shear-enhanced compaction, permeability was primarily controlled by the effective mean stress, independent of the deviatoric stresses. With the onset of shear-enhanced compaction, however, coupling of the deviatoric and hydrostatic stresses induced considerable permeability and porosity reduction. 相似文献
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Gernold Zulauf 《International Journal of Earth Sciences》1993,82(3):489-504
Investigations of brittle deformation structures, present within the crystalline rocks of the Bavarian Oberpfalz, reveal a complex late to post-Variscan crustal evolution. Upper Carboniferous (mainly Westphalian) granites were emplaced into semibrittle to brittle rocks of the ZEV (zone of Erbendorf-Vohenstrauß) and the EGZ (Erbendorf greenschist unit), respectively. From both the alignment of the granites and the direction of granite-related tension gashes a north-east-south-west extension must be assumed for the period of magmatic activities. Apart from the granite intrusions, rapid crustal uplift (about 1.5 km/my) led to an increase in the geothermal gradient from < 30 °C/km (late Variscan pre-granitic) to > 40 °C/km (late Variscan post-granitic). The increased geothermal gradient persisted during the succeeding reverse faulting which results from late Carboniferous (probably Stephanian) east-west and northeast-south-west compression. Although not evidenced directly in the area considered, strike-slip faults seem to have played an important part during the late Variscan crustal evolution, particularly in the Early Permian. The strike-slip events indicate further crustal shortening and indentation under north-south compression.A similar indentation was present in Cretaceous time. After a weak phase of Early Cretaceous reverse faulting, which results from north-south compression, strike-slip faults formed under north-west-south-east and north-south compression. All these faults, in particular the strike-slip faults, seem to be related to the Cretaceous and lowermost Tertiary convergence of the Alpine/Carpathian orogeny.A late stage of crustal extension, characterized by a radial stress tensor (2 = 3), is indicated through high angle normal faults which probably formed during the subsidence of the adjacent Neogene Eger Graben. 相似文献
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E. Gonzalez-Clavijo M. A. Diez-Balda F. Alvarez 《International Journal of Earth Sciences》1993,82(3):448-460
The Villalcampo shear system is a regional dextral strike-slip fault zone that affects Late Variscan granites and their metamorphic country rocks over an area of about 150 km2. The detailed geometry of this subvertical north-west—south-east shear zone is outlined. The system forms an extensional fan to the northwest and extends to the south-east as a broad extensional duplex. Particular attention is focused on the distribution of fault rocks and associated veins in its north-west splay. A structural study of the shear bands (encompassing both geometric and kinematic criteria) and a microscopic study of the fault rocks has led to the interpretation of the system as a brittle—ductile shear zone. Calculations give a shear strain value of = 1.5 and a minimum displacement of s = 3700 m. The localization of gold mineralization in mylonite-filled subvertical extensional veins is a product of the formation of the Villalcampo shear system. The subvertical faults and veins underwent a process of cyclical sealing and reopening. As such they acted as valves controlled by fluid pressure regulating fluid—rock interactions and gold deposition. Conditions favouring these processes occur near the base of the seismogenic zone in the vicinity of the frictional—quasi-plastic transition at mid-greenschist metamorphic conditions (T = 350°C and 10–15 km depth). 相似文献
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Effect of brittle fracture on the rheological structure of the lithosphere and its application in the Ordos 总被引：2，自引：0，他引：2
An empirical formula for the fracture strength of the principal rock type in the lithosphere is obtained based on the experimental data from previous studies, in which the effects of the confining pressure, size of the rock sample, temperature, strain rate and the pore pressure are taken into account, the empirical formulae for the effects of them are also presented. By comparing the frictional strength to the fracture strength calculated using the new empirical formula, it is shown that frictional sliding is dominant in the upper crust but brittle fracture is dominant in the lower part of the crust and the lithosphere beneath the crust. Therefore the fracture mechanism must be taken into account in the study of the rheological structure of the lithosphere. The empirical formula for the fracture strength is applied to study the rheological structure of the lithosphere in the Ordos block. Brittle regime in the rheological structure can be divided into two sub-regions, in one of which brittle fracture and in the other frictional sliding are dominant, respectively, unlike previous conventional studies in which frictional sliding is assumed to be the only factor; the magnitude of the rheological strength of the lithosphere calculated by the empirical formula is also lower than that obtained in previous conventional studies. 相似文献
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