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1.
舒兰北东向韧性剪切带位于佳木斯-伊通断裂带(佳-伊断裂带)中南段, 剪切带内糜棱岩具有明显左行走滑特征, 片麻理产状近NNE向.糜棱岩中长石有限应变Flinn图解判别岩石类型为L-S型构造岩, 属拉长型应变.石英C轴EBSD组构分析表明, 石英组构以中低温菱面为主, 滑移系为{0001} < 110>.剪切带内糜棱岩的剪应变为0.44, 不同方法计算所得运动学涡度值均大于0.95, 指示剪切变形以简单剪切为主.综合矿物变形温度计、石英C轴EBSD组构、石英的粒度-频数图及Kruhl温度计综合估计该韧性剪切带变形机制以位错蠕变机制为主, 变质相为低绿片岩相, 发生韧性变形和糜棱岩化温度范围在400~500 ℃之间.糜棱岩内石英动态重结晶新晶粒边界普遍具有锯齿状或港湾状结构, 利用分形方法对其重结晶新晶边界研究表明, 这些晶粒边界具有自相似性, 表现出分形特征, 分形维数值为1.195~1.220.根据石英重结晶粒径估算差应力值为24.35~27.59 MPa, 代表了舒兰韧性剪切带糜棱岩化作用过程的差异应力下限.使用不同实验方法估算、比较和分析了该剪切带古应变速率, 认为该速率应为10-12.00~10-13.18 s-1, 与区域性应变速率10-13.00~10-15.00 s-1对比, 说明舒兰韧性剪切带的应变速率与世界上大多数韧性剪切带中的糜棱岩应变速率一致, 是缓慢变形的结果, 其形成可能与早白垩世伊泽纳崎板块向欧亚大陆俯冲发生转向有关. 相似文献
2.
U. Ring 《International Journal of Earth Sciences》1998,86(4):786-801
This study explores the state of finite strain and changes in the mean kinematic vorticity number, grain size, whole-rock chemistry and mineralogy across an upper amphibolite-facies shear zone in a metadiorite, northern Malawi, east-central Africa. P–T conditions during shear-zone formation and deformation were approximately 700–750?°C and 5–7?kbar and are slightly less than P–T conditions for the regional peak of metamorphism. The major rock-forming minerals, plagioclase, hornblende, biotite, and quartz, were deformed by crystal-plastic processes accompanied by, except for hornblende, dynamic recrystallization. The modal abundance of all four major rock-forming minerals shows no systematic change from the country rock into and across the shear zone, indicating that shear-zone development was not associated with retrograde mineral reactions. The grain size of the major rock-forming minerals decreases within the shear zone. Plagioclase and hornblende, which occur as porphyroblasts outside the shear zone, exhibit a bimodal grain-size distribution within the shear zone. Quartz has a unimodal grain-size distribution in the shear zone. Major and trace element chemistry does not change systematically across the shear zone, implying no volume change in the mylonite. Matrix strain data for plagioclase and hornblende by the Fry method and fabric strain as deduced from Rf/φ analysis of plagioclase and quartz grains demonstrate a slightly constrictional strain type (K≈1.5) across the shear zone. The quantitative finite-strain data for the different residual minerals as obtained by unlike methods show no systematic variation, but recrystallized plagioclase grains record higher strain than the residual grains. The mean kinematic vorticity number changes from approximately 0.3 outside to approximately 0.8 within the shear zone, indicating that the bulk deformation path deviated from progressive simple shear. The estimates for finite strain and the degree of noncoaxiality account for approximately 50% of thinning normal to the shear zone. 相似文献
3.
Feldspar grain-size reduction occurred due to the fracturing of plagioclase and K-feldspar, myrmekite formation and neocrystallization of albitic plagioclase along shear fractures of K-feldspar porphyroclasts in the leucocratic granitic rocks from the Yecheon shear zone of South Korea that was deformed under a middle greenschist-facies condition. The neocrystallization of albitic plagioclase was induced by strain energy adjacent to the shear fractures and by chemical free energy due to the compositional disequilibrium between infiltrating Na-rich fluid and host K-feldspar. With increasing deformation from protomylonite to mylonite, alternating layers of feldspar, quartz and muscovite developed. The fine-grained feldspar-rich layers were deformed dominantly by granular flow, while quartz ribbons were deformed by dislocation creep. With layer development and a more distributed strain in the mylonite, lower stresses in the quartz-rich layers resulted in a larger size of dynamically recrystallized quartz grains than that of the protomylonite. 相似文献
4.
A detailed structural and microstructural analysis of the Miocene Raft River detachment shear zone (NW Utah) provides insight into the thermomechanical evolution of the continental crust during extension associated with the exhumation of metamorphic core complexes. Combined microstructural, electron backscattered diffraction, strain, and vorticity analysis of the very well exposed quartzite mylonite show an increase in intensity of the rock fabrics from west to east, along the transport direction, compatible with observed finite strain markers and a model of ``necking'' of the shear zone. Microstructural evidence (quartz microstructures and deformation lamellae) suggests that the detachment shear zone evolved at its peak strength, close to the dislocation creep/exponential creep transition, where meteoric fluids played an important role on strain hardening, embrittlement, and eventually seismic failure.Empirically calibrated paleopiezometers based on quartz recrystallized grain size and deformation lamellae spacing show very similar results, indicate that the shear zone developed under stress ranging from 40 MPa to 60 MPa. Using a quartzite dislocation creep flow law we further estimate that the detachment shear zone quartzite mylonite developed at a strain rates between 10−12 and 10−14 s−1. We suggest that a compressed geothermal gradient across this detachment, which was produced by a combination of ductile shearing, heat advection, and cooling by meteoric fluids, may have triggered mechanical instabilities and strongly influenced the rheology of the detachment shear zone. 相似文献
5.
位于北喜马拉雅穹隆带东段的然巴构造穹隆外围发育环形韧性剪切带,带内岩石经韧性剪切形成各类糜棱状岩石。石英为带内变形岩中最为常见的造岩矿物,在不同的温度、应变速率下产生不同的显微构造,其中动态重结晶最为常见。重结晶新晶颗粒边界普遍具有锯齿状或港湾状结构,是应变和变形环境的天然记录。新晶粒分维几何统计分析表明:带内动态重结晶石英颗粒边界形态具有自相似性(1≤D≤2),表现出分形特征,分维数值为1.14～1.19,变形温度大约500℃。同构造变质环境属中——高绿片岩相;初步估算古应变速率可能低于10-9.5S-1;根据重结晶粒径估算变形古应力6.2～58.8MPa。 相似文献
6.
LIANG Chenyue LIU Yongjiang ZHENG Changqing LI Weimin Franz NEUBAUER ZHANG Qian 《《地质学报》英文版》2019,93(5):1477-1499
The calcite mylonites in the Xar Moron-Changchun shear zone show a significance dextral shearing characteristics. The asymmetric(σ-structure) calcite/quartz grains or aggregates, asymmetry of calcite c-axes fabric diagrams and the oblique foliation of recrystallized calcite grains correspond to a top-to-E shearing. Mineral deformation behaviors, twin morphology, C-axis EBSD fabrics, and quartz grain size-frequency diagrams demonstrate that the ductile shear zone was developed under conditions of greenschist facies, with the range of deformation temperatures from 200 to 300°C. These subgrains of host grains and surrounding recrystallized grains, strong undulose extinction, and slightly curved grain boundaries are probably results of intracrystalline deformation and dynamic recrystallization implying that the deformation took place within the dislocation-creep regime at shallow crustal levels. The calculated paleo-strain rates are between 10~(–7.87)s~(–1) and 10~(–11.49)s~(–1) with differential stresses of 32.63–63.94 MPa lying at the higher bound of typical strain rates in shear zones at crustal levels, and may indicate a relatively rapid deformation. The S-L-calcite tectonites have undergone a component of uplift which led to subhorizontal lifting in an already non-coaxial compressional deformation regime with a bulk pure shear-dominated general shear. This E-W large-scale dextral strike-slip movement is a consequence of the eastward extrusion of the Xing'an-Mongolian Orogenic Belt, and results from far-field forces associated with Late Triassic convergence domains after the final closure of the Paleo-Asian Ocean. 相似文献
7.
We use quantitative microstructural analysis including misorientation analysis based on electron backscatter diffraction (EBSD) data to investigate deformation mechanisms of naturally deformed plagioclase in an amphibolite gabbro mylonite. The sample is from lower oceanic crust exposed near the Southwest Indian Ridge, and it has a high ratio of recrystallized matrix grains to porphyroclasts. Microstructures preserved in porphyroclasts suggest that early deformation was achieved principally by dislocation creep with subgrain rotation recrystallization; recrystallized grain (average diameter ∼8 μm) microstructures indicate that subsequent grain boundary sliding (GBS) was active in the continued deformation of the recrystallized matrix. The recrystallized matrix shows four-grain junctions, randomized misorientation axes, and a shift towards higher angles for neighbor-pair misorientations, all indicative of GBS. The matrix grains also exhibit a shape preferred orientation, a weak lattice preferred orientation consistent with slip on multiple slip systems, and intragrain microstructures indicative of dislocation movement. The combination of these microstructures suggest deformation by dislocation-accommodated GBS (DisGBS). Strain localization within the recrystallized matrix was promoted by a transition from grain size insensitive dislocation creep to grain size sensitive GBS, and sustained by the maintenance of a small grain size during superplasticity. 相似文献
8.
Debasis Sen Gupta 《Journal of Earth System Science》1995,104(3):407-417
Recrystallized grain size was measured from quartzite mylonite specimens collected from parts of Singhbhum shear zone in eastern
India. The specimens were collected along five traverses (Mushabani, Pathargora, Surda, Rakha and Jadugoda) across the elongation
of the shear zone. The sheared quartzites range from protomylonite through mylonite to ultramylonite. The microstructural
studies of the specimens reflect that dynamic recrystallization was the main deformation process. Estimation of flow stresses
were derived from these specimens using empirical equations relating to flow stress and recrystallized grain size. The calculated
stresses range from 12–28 MPa (Mercieret al 1977), 23–49 MPa (Twiss 1977), 20–68 MPa (Christie and Ord 1980), considering all the traverses. The results show that these
values can only be used semiquantitatively. 相似文献
9.
Recrystallized grain sizes, subgrain sizes and dislocation densities of quartz grains in quartzose mylonitic rocks have been examined using optical and transmission electron microscopy (TEM). The samples come from the Moine Thrust zone in the Assynt district, Scotland. They had been studied previously and described in detail with respect to their structural position in relation to the various thrusts in the region and to their preferred orientation. Stresses were derived from these samples using empirical and theoretical equations relating flow stress to the scale of the microstructures. The stresses determined, 43–244 MPa from recrystallized grain size, 9–13 MPa from etched subgrain size, 50–95 MPa from TEM-scale subgrain size and 75–147 MPa from dislocation density, are not constant in individual samples. Simultaneous formation of the quartz fabrics and of the dynamically recrystallized grains during the period of mylonitization may have occurred under flow stresses ranging from 43 to 244 MPa. A later dynamic recovery event reset subgrain sizes and dislocation densities to a constant-value for each microstructure throughout the area. There is insufficient empirical information available on the flow stress/subgrain size relationship and on the effects of annealing recovery and annealing recrystallization to allow for a more detailed interpretation. Recrystallized grain size is still the most easily measured microstructural feature and the relationship of recrystallized grain size to flow stress has a sounder experimental basis than subgrain size or dislocation density. The effect of chemical environment on the behaviour of all the microstructures is still unknown. 相似文献
10.
AbstractThe Cadomian Dyje Batholith, in the foot–wall of the Variscan Moravian nappe pile, has been involved in Variscan ductile deformation. The Cadomian Brunovistulian rocks were obliquely underthrusted during Carboniferous dextral transpression.Strain intensity is inversely proportional to the distance from the contact of the Variscan thrust front. The microstructures of deformed granodiorites and quartz–diorites show a characteristic zonality marked by relatively high temperature flow in the west (550–580 °C) characterized by dynamic recrystallization of feldspars and grain boundary migration recrystallization of quartz. The size of quartz grains decreases with decreasing strain towards the east. At the easternmost part of the autochthonous Dyje massif, fracturing of feldspar and subgrain rotation recrystallization of quartz predominate. Flow stress estimates calculated from recrystallized quartz grain size show a regional increase of stress intensity from the highly strained margin towards the less deformed core of the Dyje massif. This microstructural zonation is oblique with respect to the major thrust boundary and corresponds roughly to metamorphic isogrades. The microstructural zonation reflects underthrusting of the Brunovistulian domain below the Moldanubian nappe.The main ductile tectonic event D1 is followed by a retrogressive brittle–ductile and brittle deformation D2. D2 results in the development of shear zones and faults superimposed on the D1 mylonite fabric. D2 is related to extension oblique to the D1 fabric, associated with detachment and the westward movement of the Moravian nappes. © Elsevier, Paris 相似文献
11.
12.
Shear zones are areas of intense deformation in localized zones which can be used as natural laboratories for studying deformation characteristics. Metre to-micro scale structures that develop in response to a progressive simple shear in a shear zone are characterized by a protracted history of deformation and are immensely useful in delineating the history of progressive deformation. To decipher these localized zones of deformation and to establish the continuous non-coaxial character of deformation, detail microstructural studies are very useful. Singhbhum shear zone (SSZ), a regional Precambrian tectonic dislocation zone in eastern India, depicting a top-to-south thrust movement of the hanging wall provides a scope for studying microstructural characteristics developed in response to a progressive shear at mid-crustal level. SSZ is characterized by intense stretching lineation, isoclinal folds, shear planes, superposed schistosity and deformed quartz veins. Quasi-plastic (QP) deformation mechanisms were predominantly active in the SSZ. The overprinting relationship between the earlier and later schistosity with a consistent sense of shear indicates that earlier schistosity is transposed to later schistosity through the intermediate stages of crenulation cleavage during a progressive non-coaxial deformation. The recrystallization of quartz in mylonitic quartzite suggests protracted history of deformation. The analysis of the character of quartz grains of both the porphyroclasts and recrystallized grains suggests that strain was partitioned between the most intensely deformed central part of the shear zone and the shear-related deformation zone outside the central part of the shear zone. 相似文献
13.
This work focuses on the development of a regional P-T-path from the Malpica-Lamego Ductile Shear Zone, NW Portugal, based on the microstructures of shearband boudins evolved during progressive simple shear. The combination of microstructural analysis, fluid inclusion studies, crystallographic preffered orientation and fractal geometry analyses, allows to link several stages in the internal evolution of the boudin to regional P-T conditions. The boudinage process is initiated under differential stress after the original layer achieved sufficient viscosity contrast relative to the surrounding matrix. Two main transformations occur simultaneously: i) change in the external shape with continuous evolution from tabular rigid body to sigmoidal asymmetric morphology (shearband boudin) and ii) localized dynamic recrystallization in the sharp-tips of the structure (acute edge of shearband boudin), and along the boudin's margin and grain boundaries. Smaller recrystallized grains, particularly in the sharp-tip domains, accommodate most of the external strain, and larger relict grains are preserved in the centre. Dynamic recrystallization under constant strain rates and strain partitioning inside the boudins is indicated by fractal geometry based on grain boundary and grain area analysis. Progressive deformation leads to the generation of structural and textural heterogeneous domains inside the boudins, and is recorded by quartz c-axis orientation analysis and fluid inclusion studies. The last deformation episode shows the final formation of the blunt-tip domain and internal secondary shear planes. The regional P-T path begins with the crystallization of andalusite after an internal shearband boudin dilation event and ends with quartz dynamic recrystallization on boudin tips. The main deformation stage (310/315 Ma) led to reactivation of internal secondary shear zones with sillimanite crystallization. 相似文献
14.
阿尔泰造山带的剪切带中发育大量S-C糜棱岩,其内云母产生云母鱼和扭折构造并发生边界重结晶。长石发生不同性质的系列变形,并以出熔成核为主的动态重结晶为主要变形机制,同时伴有强烈的扩散作用,属Naborrow-Herring蠕变。石英的变形呈条带状并发生完全的旋转和边界迁移动态重结晶。石英晶内变形以位错运动和动态恢复为主,形成亚颗粒构造及动态重结晶,以致产生应变弱化和超塑性变形,定量分析确定的石英变形机制主要为低温幂指数蠕变。 相似文献
15.
A natural example of crystal-plastic deformation enhancing the incorporation of water into quartz 总被引：2，自引：0，他引：2
Water content of quartz in and around a greenschist facies mylonitic shear zone located in the western Adirondacks was analyzed by micro-FTIR spectroscopy. The shear zone is within a pegmatitic dike, which cuts across a granitic gneiss. The thickness of the shear zone varies along strike from 15 cm wide and encompassing all of the pegmatite dike at its northern most exposure to 5 cm wide approximately 10 m south, along strike. Microstructures, including quartz ribbons and recrystallized grains, indicate quartz and feldspar within the mylonite underwent dislocation creep. Infrared spectral analysis was carried out using a Nicolet micro-FTIR on mylonitic quartz ribbons, pegmatitic quartz and gneissic quartz. A small aperture size (56 μm by 50 μm) for the IR beam allowed optically clear regions of the quartz grains to be analyzed without any contribution from grain boundaries. The smallest dimension of the quartz ribbons is 0.3 mm, whereas the pegmatitic quartz has a grain size of 3 to 5 cm. Results show mylonitic quartz ribbons contain the most water (320 H:106 Si average, range of 50 to 1120 H:106 Si); pegmatite quartz contains much less water (30 H:106 Si average, range of 20–40 H:106 Si) and the gneissic quartz contained an intermediate amount (200 H:106 Si average, range of 20 to 870 H:106 Si). These data indicate that water was preferentially incorporated into the deformed quartz ribbons. 相似文献
16.
The analysis of fabric and microstructure across an amphibolite facies shear zone of mafic composition reveals that the strain-dependent change from grain size insensitive to grain size sensitive creep is associated with a fundamental reorganization of the mylonitic fabric. At moderate strain a banded mylonite evolves from a metagabbro, which displays a mechanically-induced compositional layering. Strain is concentrated in monomineralic layers of dynamically recrystallized plagioclase. At higher strain and decreasing grain size (10-30 µm) the phase segregation is progressively destroyed and replaced by a phase mixture of amphibole and plagioclase. Phase mixing in these ultramylonites is developed and stabilized by heterogeneous nucleation processes of amphibole and plagioclase within unlike phases and at dilatant sites. Nucleation appears to be controlled by grain-scale gradients in stress. A dispersed phase distribution in fine-grained ultramylonites indicates (water-assisted) diffusion processes that accommodate grain boundary sliding. Although diffusion-controlled creep plays a dominant role in these ultramylonites, the dislocation densities remain high (2.0-4.0᎒9 cm-2) and indicate that two competing mechanisms (dislocation and diffusion creep) accommodate grain boundary sliding. Commonly accepted criteria for superplastic or granular flow derived from monomineralic aggregates must be applied with caution to polymineralic rocks of mafic composition. 相似文献
17.
Mylonitization of medium-grade marbles in the Bancroft shear zone, Ontario, Canada, is characterized by decreasing grain-size of both calcite and graphite, and a variety of textures. Calcite grain-sizes vary from several millimeters in the protolith, to 50–200 μm in mylonite, to <30 μm in ultramylonite. Corresponding calcite grain shapes are equant in the protolith, elongate in protomylonite (first-developed dimensional preferred orientation), equant in coarse mylonite, elongate in fine mylonite (second-developed dimensional preferred orientation) and generally equant in ultramylonite, which suggests that external energy (applied stress) that tends to elongate grains competed with internal energy sources (e.g. distortional strain) that favor equant shapes. Graphite grain-size changes from several millimeters to centimeters in the protolith to submicroscopic in ultramylonite. In the mylonitic stages, graphite is present as dark bands, while in the ultramylonitic stage it is preserved as a fine coating on calcite grains.Based on textural evidence, twinning (exponential creep; regime I), dynamic recrystallization (power law creep; regime II) and possibly grain boundary sliding superplasticity (regime III) are considered the dominant deformation mechanisms with increasing intensity of mylonitization; their activity is largely controlled by calcite grain-size. Calcite grain-size reduction occurred predominantly by the process of rotation recrystallization during the early stages of mylonitization, as indicated by the occurrence of core and mantle or mortar structures, and by the grain-size of subgrains and recrystallized grains. Grain elongation in S-C structures indicates the activity of migration recrystallization; these structures are not the result of flattening of originally equant grains. Differential stress estimates in coarse mylonites and ultramylonites, based on recrystallized grain-size, are 2–5 and 14–38 MPa, respectively. Initial grain-size reduction of graphite occurred by progressive separation along basal planes, analogous to mica fish formation in quartzo-feldspathic mylonites.Calcite-graphite thermometry on mylonitic and ultramylonitic samples shows that the metamorphic conditions during mylonitization were 475 ± 50°C, which, combined with a differential stress value of 26 MPa, gives a strain rate of 1.2 x 10−10s−1 based on constitutive equations; corresponding displacement rates are <38 mmyr−1. 相似文献
18.
长乐-南澳韧性剪切带糜棱岩的显微变形机制有粒间滑动、粒内滑动、位错及其滑移和蠕变、应变的局部恢复等。石英丰富的韧性变形和位错特征以及长石的脆一弹性变形说明糜棱岩形成于绿片岩相条件,变形时的温度约为300-350℃。石英塑性变形处于重结晶一软化阶段和热加工一恢复阶段。由位错密度和动态重结晶颗粒粒径计算了差异应力和应变速率,分别为56.8-99.7MPa,(0.35-1.61)×10-13s-1和175.8-406.9MPa,(0.7-7.2)×10-12s-1,二者较大的差值表明糜棱岩是缓慢上升至地表的,这一结论与应变局部恢复现象一致。该韧性剪切带是闽粤沿海早白垩世末碰撞造山的产物。 相似文献
19.
Plastically deformed quartzites from the Betic Movement Zone (Betic Cordilleras, Spain) exhibit microstructures indicative of crystal plasticity on a mineral grain scale. Quartzites with dynamically recrystallized grain sizes larger than 10 μm have strong crystallographic preferred orientations, narrow grain boundaries, little creep damage, and an inverse proportionality of dislocation density and grain size. Mylonites with grain sizes smaller than 10 μm have low crystallographic preferred orientations, wide grain boundaries (up to 1000 Å), abundant creep damage, and decreasing dislocation density with diminishing grain size. This is thought to reflect a clear-cut shift in deformational regimes from dislocation creep to superplastic flow at 10 μm grain size. Superplasticity can be acquired by quartzites which suffer dynamic recrystallization to grain sizes smaller than 10 μm during an initial dislocation creep stage. Dislocation motion is the major accomodating mechanism for strain incompatibilities that arise during grain-boundary sliding in the mylonites.It seems reasonable to estimate flow stresses from unbound dislocation densities and dynamically recrystallized grain sizes in the tectonite specimens. In the mylonites, dynamically recrystallized grain size probably reflects the stress magnitude before the shift in deformational mechanisms, and an estimate for late stage stresses is provided by unbound dislocation densities. In both deformational regimes the flow strength appears to depend on the extent of dynamic recrystallization. 相似文献
20.
糜棱岩韧性变形发生的应变局部化过程,尤其是多相糜棱岩第二相对基质相变形的影响一直是显微构造研究难点.研究表明糜棱岩借助颗粒边界滑移实现多相混合,形成多矿物相集合体.在多相糜棱岩内,第二相在基质相颗粒边界施加齐纳阻力,牵制基质相颗粒边界的迁移速率,破坏基质相颗粒的动态平衡过程,使基质相颗粒位于古应力计对应的颗粒粒度以下,导致基质相整体的表面积增大,促进扩散交换过程,提高了扩散蠕变,降低了基质相位错蠕变和结晶学优选方位(CPO)形成的效率,使变形机制从颗粒粒径不敏感蠕变机制(GSI)过渡为颗粒粒径敏感蠕变机制(GSS).另外,多相糜棱岩内的第二相具有诱导应变局部化的效应,使塑性应变局部化更为强烈,引起物质强度的变化,进而引起岩石变形过程和岩石圈流变行为的改变.选取秦岭群花岗质糜棱岩进行多相矿物糜棱岩定量化研究,结果显示花岗质糜棱岩伴随着云母含量的增多以及各相混合程度的增大,石英的颗粒粒度明显减小,CPO强度显著降低,基质相显微变形受第二相控制逐渐增强. 相似文献