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1.
Samples of San Marcos gabbro were deformed to both pre- and post-failure stages at confining pressures of 100, 250 and 350 MPa. Scanning electron microscope observations were performed on the samples after ion-milling. The unstressed gabbro has insignificant crack porosity but a high volume fraction of healed and sealed cracks. Extensive stress-induced cracking at high angles to the maximum compressive stress is observed at the two higher pressures. Such high-angle cracks are mostly associated with the pre-existing healed cracks or cleavage planes, and they control the geometry and length scale of crack networks in plagioclase. Intensive kinking in biotite is widely observed at 350 MPa pressure, which together with the crack networks control the brittle fracture process. Stress-induced cracks in samples deformed at 100 MPa pressure are predominantly subparallel to the maximum compressive stress, and their coalescence leads to shear localization.Quantitative measurements of crack density as a function of differential stress indicate that crack interaction is appreciable beyond about 90% peak stress for all three pressures. The data also show significant decreases in stress-induced anisotropy as pressure increases, suggesting that there may be a threshold pressure beyond which stress-induced anisotropy vanishes with the onset of cataclasis. 相似文献
2.
Syntectonic plutons emplaced in shallow crust often contain intermediate-to low-temperature deformation microstructures but
lack a high-temperature, subsolidus deformation fabric, although the relict magmatic fabric is preserved. The Proterozoic
Vellaturu granite emplaced at the eastern margin of the northern Nallamalai fold belt, south India during the late phase of
regional deformation has a common occurrence of intermediate-to low-temperature deformation fabric, superimposed over magmatic
fabric with an internally complex pattern. But high-T subsolidus deformation microstructure and fabric are absent in this
pluton. The main crystal plastic deformation and fluid enhanced reaction softening was concentrated along the margin of the
granite body. Resulting granite mylonites show Y-maximum c-axis fabric in completely recrystallized quartz ribbonds, dynamic recrystallization of perthites, and myrmekite indicative
of fabric development under intermediate temperature (∼ 500–400°C). The weakly-deformed interior shows myrmekite, feldspar
microfracturing and limited bulging recrystallization of quartz. The abundance of prism subgrain boundaries is indicative
of continuing deformation through low-temperature (∼ 300°C). The relative rates of cooling influenced by advective heat transfer
and deformation of the pluton seem to control the overall subsolidus fabric development. The rapid advective heat transfer
from the interior in the early stages of subsolidus cooling was followed by slow cooling through intermediate temperature
window as a well-developed phyllosilicate rich mylonitic skin around the granite body slowed down conductive heat loss. Low-T
crystal plastic deformation of quartz was effected at a late stage of cooling and deformation of the shallow crustal granite
body emplaced within the greenschist facies Nallamlai rocks. 相似文献
3.
以CCD相机配合高速相机搭建试验变形观测系统,开展不同加载速率下含Ⅰ型预制裂纹花岗岩试件的三点弯试验。利用数字散斑相关方法对试验过程采集的数字散斑图像进行分析,对不同加载速率作用下含Ⅰ型预制裂纹花岗岩试件裂纹扩展过程中的变形演化特征、裂纹扩展速率、裂纹尖端张开位移、裂纹张开角以及初始断裂应力强度因子进行研究,研究结果表明：（1）花岗岩试件初始裂纹扩展速率随着加载速率的增加总体呈线性增加趋势;最大扩展速率随着加载速率增加呈现先较快增加后缓慢增加的变化趋势。（2）不同加载速率作用下,花岗岩试件预制裂纹尖端张开位移均呈现非线性缓慢增长-迅速增长-线性增长的变形趋势,且线性增长阶段曲线斜率随着加载速率的增加而增大。（3）随着加载速率的增加,花岗岩试件初始裂纹张开角先逐渐减小后稳定在0.1o～0.13o。（4）随着加载速率的增加,花岗岩试件初始断裂应力强度因子呈指数增长。 相似文献
4.
Youqing Chen Kota Watanabe Hiromu Kusuda Eishi Kusaka Mamoru Mabuchi 《Engineering Geology》2011,117(3-4):189-197
To examine the fatigue process of granite, cylindrical Westerly granite specimens, 10 mm in diameter and 20 mm in length, were subjected to a cyclic loading test under uniaxial compression with a maximum of 140 MPa at room temperature, and crack growth patterns within them were analyzed by microscopic observation and image analysis techniques. The fatigue process is divided into three characteristic stages; a primary stage in which the upper peak strain increases at a decelerating rate (stage I), a second stage with linearly slight increasing rate of strain following stage I (stage II), and the third and final stage in which the upper peak strain increases at an accelerating rate and culminates in specimen failure (stage III). A series of prefailure specimens, of which the stage in the fatigue process was decided by monitoring the strain behavior during the test, were retrieved. In addition, these specimens were compared with specimens stressed to close to the breaking strength by monotonic compression to examine the characteristic features of fatigue. The fluorescent method was applied to identify microcracks within the specimens. The advantage of this method is to provide quick and accurate identification of microcracks with an optical microscope. Microcracks are detected based on a marked difference in brightness under ultraviolet light irradiation because they are fully filled with acrylic resin mixed with a fluorescent substance in advance. Thin sections, including the axis of the specimen, 10 × 20 mm, were prepared for detailed observation after the pretreatment of the method.The results were as follows. At the initial degradation stage, distinguishing crack growth was identified in quartz grains. It is estimated that the slowdown of the strain growth rate at this stage was caused by the decrease in crack growth, that is, the portions with cracking potentiality were damaged at the first or early loading, and no further damage occurred immediately following the first damage. At the second stage, no significant crack growth in quartz grains was identified. On the other hand, in feldspar grains, development of cracks in a preferential direction, parallel to the loading direction, was observed. However, they did not grow into intergranular cracks by cutting across the grain boundaries during this stage. Consequently, it was found that a gradual progress of microcracks within feldspar grains was dominant during the second stage, and this is because the strain growth rate was in a steady and long state. At the final accelerated stage, many intergranular cracks running parallel to the loading direction were identified. It is obvious that these long cracks were formed mainly by the linking and growth of the intragranular cracks in feldspars, which were generated during the former stages. Their formation takes the fatigue process from the second stage to the final stage with a sharp increase in strain, and their further development seemed to lead the whole specimen to ultimate fatigue failure. 相似文献
5.
6.
E.G. Bombolakis 《Tectonophysics》1973,18(3-4)
Static friction along inclined cracks in photoelastic models increases with both the loading and frictional displacement before the larger crack-wall asperities are broken or completely over-ridden. Elastic shocks resulting from successive stick-slip during this stage can be repeated more or less indefinitely with repeated loading and unloading. Locked-in residual stresses, especially around crack tips, result when the model is unloaded, because of frictional coupling between crack walls. Favorable crack arrays for initial growth in the model include particular sets of en-echelon cracks inclined 45° to the stress axis, but the critical orientation may be smaller in brittle rock if crack-wall friction in rock is greater than in the model. Axial growth of en-echelon cleavage cracks, inclined at angles smaller than 45°, was observed in feldspar during deformation of a pegmatite having a mineralogy and texture similar to granite. Their growth follows predictions derived from photoelastic model studies.Crack growth in the pegmatite begins between half and two-thirds of the ultimate strength. The first flaws to grow, however, also include pre-existing axially oriented cleavage cracks in the feldspar. Crack growth occurs randomly throughout the specimen as stress is increased, without much evidence that grain boundaries are activated for crack growth. But when the applied stress approaches the ultimate strength, two new features are observed. There is an abrupt development of finite frictional slip along favorably inclined flaws and grain boundaries, beginning with displacements of the order of the dimensions of grain-boundary asperities. Crack growth still occurs at various locations throughout the specimen at this stage, but there is also a detectable concentration of growth along potential shear zones. Flaw-wall friction appears to be one of the critical factors that determine the pegmatite's ultimate strength and the instability of through-going fracture. 相似文献
7.
微裂隙对于岩石的物理性质有重要影响.通过光学显微镜对显微裂隙进行的观察,难以将薄片的制作过程中产生的裂隙同自然裂隙区分;其次,观测的裂隙大小限制在0.1mm或以上数量级,一些重要细节观察不到.扫描电镜的高放大倍数和三维分辨率使其成为适合于裂隙研究的理想工具.利用扫描电镜观测了浙江花岗岩在室温下由51.6MPa压力产生的裂隙的发育过程.观察花岗岩的表面以研究其微裂隙和矿物的解理、晶形及破裂作用.微裂隙分为3种类型:晶体内裂隙(完全发育在颗粒内部),晶体间裂隙(穿过颗粒边界进入其他颗粒中),颗粒边界裂隙(沿颗粒边界发育或与边界重合).本研究中的花岗岩为中—粗粒(1～6mm),经过蚀变,约含40%斜长石,25%钾长石,25%石英,10%镁铁矿物(主要为黑云母和白云母).(1)石英裂隙表面的石英颗粒具有边界破裂和贯穿颗粒破裂.贯穿石英颗粒的破裂常呈贝壳状断口.变形集中带与滑动面相伴,其上发育有擦痕和沟槽,这是石英典型的脆性破裂类型.石英矿物的贝壳状破裂产状指示其变形作用早期的碎裂作用,在变形作用中发生交代作用.一些平滑的破裂面上没有石英颗粒的微裂隙构造,但在石英表面却有明显的擦痕面,可指示应力的方向.由于石英的各向异性,这些面也是由贯穿颗粒破裂所形成.一些开放的裂隙集中于石英晶体之中或沿 相似文献
8.
微裂隙对于岩石的物理性质有重要影响.通过光学显微镜对显微裂隙进行的观察,难以将薄片的制作过程中产生的裂隙同自然裂隙区分;其次,观测的裂隙大小限制在0.1mm或以上数量级,一些重要细节观察不到.扫描电镜的高放大倍数和三维分辨率使其成为适合于裂隙研究的理想工具.利用扫描电镜观测了浙江花岗岩在室温下由51.6MPa压力产生的裂隙的发育过程.观察花岗岩的表面以研究其微裂隙和矿物的解理、晶形及破裂作用.微裂隙分为3种类型:晶体内裂隙(完全发育在颗粒内部),晶体间裂隙(穿过颗粒边界进入其他颗粒中),颗粒边界裂隙(沿颗粒边界发育或与边界重合).本研究中的花岗岩为中-粗粒(1~6mm),经过蚀变,约含40%斜长石,25%钾长石,25%石英,10%镁铁矿物(主要为黑云母和白云母). 相似文献
9.
为研究花岗岩在三轴循环加卸载条件下气体渗透率的演化规律,利用岩石多场耦合三轴试验仪分别对花岗岩进行三轴恒下限分级循环加卸载试验和气体渗透试验。试验结果表明：加载曲线与上一次循环卸载曲线形成塑性滞回环,随着循环次数的增加,每个循环应力下限的轴向应变也随之增加;前期几个循环试样体积压缩明显,以轴向压缩变形为主,后期轴向应力达到一定数值时体积由压缩转为扩容,裂纹发展方向偏向于轴向方向,均呈剪切脆性破坏;气体渗透率变化分为稳定下降阶段、缓慢增加阶段、急剧上升阶段3个阶段,试样脆性破坏后气体渗透率均上升2～3个数量级;体积应变曲线拐点与横向应变曲线结合起来可以作为研究岩石渗透率变化规律的一个重要参考因素。 相似文献
10.
辽南金州拆离断层带中花岗质岩石的变形:显微构造、组构与年代学分析 总被引：1，自引：0，他引：1
花岗岩(脉)在中下地壳韧性剪切带中普遍发育,如何正确鉴别剪切带中剪切前、剪切期及剪切后花岗岩(脉)以及正确理解剪切过程中构造变形与岩浆作用之间的关系一直是一个重要课题。本文以辽南金州拆离断层带为研究对象,选取中部地壳伸展作用过程中具有不同变形表现的花岗岩(脉)开展宏观-微观构造观察、石英EBSD组构分析及锆石LA-ICP-MS年代学测试等工作,从而进一步丰富构造-岩浆关系判别准则。剪切前花岗岩(脉)多变形强烈且具有后期固态变形叠加在早期高温岩浆组构之上的特点,而剪切期的花岗岩由于侵位的时间不同,岩石的变形程度也会不同。剪切晚期侵入的岩脉遭受了较弱的晶内塑性变形,而剪切早期的岩脉可以显示岩浆流动或结晶后高温至中温固态变形。从组构特点上看,剪切前和剪切期花岗质岩石石英c轴组构大多表现为中高温组构叠加有低温组构的特点。剪切后的花岗质岩石仅发生微弱的晶内变形或未变形而显示低温或无规律的组构特征。对五个典型的样品进行年代学测试,其结果符合相应的期次划分类型。应用宏观构造、显微构造与组构分析,结合年代学测试综合分析,对于辽南变质核杂岩构造-岩浆活动性进行了精细划分,包括134~130Ma初始伸展阶段,130~115Ma峰期伸展与强烈岩浆活动阶段,以及115Ma前后伸展作用结束。 相似文献
11.
In the Dora Maira Massif, western Alps, essentially undeformed ultrahigh-pressure (UHP) metamorphic granites (Brossasco granite) are embedded in, and locally grade into, granite gneisses or augengneisses and mylonites. In this study, the quartz microfabrics of the undeformed granites are compared against the augengneisses and mylonites in a representative number of samples from several locations. In the undeformed granites, the fine-grained quartz aggregates that formed from coesite upon decompression are characterized by a foam structure and random crystallographic orientation. In the deformed granites, the quartz microstructures and the crystallographic preferred orientation (CPO) indicate deformation by dislocation creep. Most of the deformation of the granites (if not all) must have happened at a late stage during exhumation, after transformation of coesite to quartz, at greenschist facies conditions in the middle crust. The deformed granites provide no evidence of deformation during subduction, at (U)HP metamorphic conditions, and in the earlier stages of exhumation. The diameter of internally undeformed slices of continental crust subducted to and exhumed from about 100 km can exceed that of the presently exposed Brossasco granite, i.e. it can be on the kilometre scale. 相似文献
12.
Stephen L. Karner Frederick M. Chester Andreas K. Kronenberg Judith S. Chester 《Tectonophysics》2003,377(3-4):357-381
Cylindrical samples of water-saturated, initially loose, St. Peter quartz sand were consolidated using triaxial deformation apparatus at room temperature, constant fluid pressure (12.5 MPa), and elevated confining pressures (up to 262.5 MPa). The samples were deformed along four loading paths: (1) hydrostatic stressing tests in which confining pressure was monotonically increased; (2) hydrostatic stress cycling similar to (1) except that effective pressure was periodically decreased to initial conditions; (3) triaxial deformation at constant effective pressure in which differential stress was applied after raising effective pressure to an elevated level; and (4) triaxial stress cycling similar to (3) except that the axial differential stress was periodically decreased to zero. Hydrostatic stressing at a constant rate results in a complex nonlinear consolidation response. At low pressures, large strains occur without significant acoustic emission (AE) activity. With increased pressure, the stress versus strain curve becomes quasi-linear with a corresponding nonlinear increase in AE rates. At elevated pressures, macroscopic yielding is marked by the onset of large strains, high AE rates, and significant grain failure. Stress cycling experiments show that measurable inelastic strain occurs at all stages of hydrostatic loading. The reload portions of stress cycles are characterized by a poro-elastic response and lower AE rates than during constant rate hydrostatic stressing. As the stress nears and exceeds the level that was applied during previous loading cycles, strain and AE rates increase in a manner consistent with yielding. Triaxial stressing cycles achieve greater consolidation and AE rates than hydrostatic loading at similar mean stress levels. By comparing our results with previously published studies, we construct a three-component model to describe elastic and inelastic compaction of granular sand. This model involves acoustically silent grain rearrangement that contributes significant inelastic strain at low pressures, poro-elastic (Hertzian) deformation at all pressures, and inelastic strain related to granular cracking and particle failure which increases in significance at greater pressures. 相似文献
13.
考虑应力历史的岩石单裂隙渗流特性试验研究 总被引：1，自引：0，他引：1
通过开展单裂隙花岗岩不同围压加、卸载和不同水力梯度作用下的渗透试验,研究应力历史对裂隙渗透性能演化的影响。试验结果表明：在围压加载过程中,渗流流量与渗透压差大致呈线性关系;在渗透压差相同的条件下,围压越小,流量越大,随着围压上升,裂隙渗流流量持续减小,但随着围压的进一步增大,流量的减小有减缓的趋势。在围压相同以及渗透压差相同的条件下,单裂隙花岗岩在卸载条件下的渗流特性与加载条件下相比,其渗流流量明显降低,且卸载过程中渗流流量与渗透压差开始偏离线性关系。从试验前、后裂隙面粗糙度系数值的对比可以看出,由于法向应力挤压以及渗流流体的冲蚀作用,试验后裂隙面粗糙度系数明显降低。卸载的过程中,裂隙渗透性能的恢复具有明显的滞后效应,表明在法向应力和流体冲蚀的共同作用下,裂隙产生了不可恢复的非弹性变形。 相似文献
14.
In high-grade (granulite facies) quartzofeldspathic rocks the progressive development of a fabric records contrasting deformation
behaviour of quartz and feldspar. Feldspar has undergone deformation mainly by recrystallization-accommodated dislocation
creep and produced smaller recrystallized grains progressively in the course of deformation. Quartz has not deformed solely
by dislocation creep but also by a diffusion-controlled mechanism. Dislocation climb is important in the dislocation creep
of quartz. In contrast to feldspar, quartz grains have not recrystallized into smaller grains at any stage of deformation.
Rather, they have transformed initially to short monocrystalline ribbons and ultimately to long polycrystalline ribbons. This
textural change of quartz is a continuous process and has taken place in the course of bulk textural change of the rocks during
the deformation. 相似文献
15.
The deformation process and failure mechanism of rock mass with increased density of initial joints subjected to confined stress state are investigated in this study using discrete element method (DEM). A numerical model of standard size granite samples is developed and validated using experimental data for both intact and jointed rocks. The micro-parameters of the rock material are first determined, and the effects of the rock discontinuity on strength, deformability, stress–strain relationship, and failure modes are then investigated at the macro-scale level. Analyses are also performed to examine the tensile and shear crack distributions, fragmentation characteristics, particle kinematics, and energy dissipation to advance the current understanding of the deformation processes and failure mechanisms of jointed rock masses. The microscopic evolutions in the fabric and force anisotropy during loading and distributions of contact forces provide insights into the influence of increasing initial jointing on the macroscopic deformational behavior of the rock. The results show how the deceleration in the growth of fabric and contact force anisotropies develops and confirms that the increase in initial jointing and the associated changes in microstructure can restrain the development of anisotropy, thereby reducing significantly the strength of the rock samples.
相似文献16.
为研究型煤在单轴压缩破裂过程中产生的微震、电磁辐射信号与裂纹演化特征的对应关系,利用自主设计的低噪声静态加载试验系统,对0～0.25、0.25～0.5、0.5～1.0、1～2 mm共4种不同粒度的型煤进行了单轴压缩破坏试验,同步采集了煤样破坏过程中的微震、电磁辐射信号及破坏视频图像,提出了一种煤体裂纹快速提取方法并计算了型煤裂纹面积的变化规律。研究结果表明：型煤在单轴压缩过程中产生的微震、电磁辐射信号及裂纹面积在时域上具有良好的同步性。型煤破坏过程中裂纹面积随时间变化曲线可分为4个阶段。第1阶段为压实阶段,煤样所受应力值较小,其表面的裂纹面积以极为缓慢的速率增加。第2阶段为初始破裂阶段,随着应力的增加和内部弹性势能的积聚,型煤表面裂纹面积的增加速率较压实阶段有明显提高,伴随产生许多细小裂纹。第3阶段为加速破裂阶段,随着应力继续增加以及材料内部积聚弹性能的释放,试样变形过程加速,导致裂纹面积增速进一步增大。第4阶段为卸压阶段,试样的裂纹面积达到最大值,承载能力急剧降低,发生失稳破坏。 相似文献
17.
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
18.
Axel Müller Paul Lennox Robert Trzebski 《Contributions to Mineralogy and Petrology》2002,143(4):510-524
Trace elements (Al, K, Ti, Fe), growth and deformation pattern in quartz of the multiple deformed Carcoar, Barry and Sunset Hills granites were investigated by electron micro probe and cathodoluminescence. Zoned quartz phenocrysts with high Ti concentrations (>70 ppm) that show blue cathodoluminescence originated from the early stage of magma crystallisation. Multiple deformation of quartz causes the redistribution of Al and K in the quartz lattice, which results in the accumulation of these elements in submicroscopic inclusions (<0.5 µm) of muscovite-like composition. In contrast, structural Ti in quartz is mostly kept in the lattice. Common halos of defect-poor, secondary quartz around fluid inclusions result from re-equilibration of fluid inclusions because of differences between fluid pressure and lithostatic pressure, e.g. during uplift (isothermal decompression) and/or !/#-transition of quartz. During healing, defect-poor secondary quartz grows at the cost of the host quartz and releases or replaces defect centres. The results of micro-structural investigations combined with Al-in-hornblende thermobarometry allow the reconstruction of regional processes. Carcoar and Barry granodiorites and Sunset Hills granite were intruded in the Late Ordovician-Early Silurian at depths of 4-8.6 and 10-12 km, respectively. In contrast to the continuous crystallisation of the granodiorite magmas, the magma of the Sunset Hills granite ascended in a stepwise fashion, causing multiple quartz nucleation. The two granodiorites were multiple, post-magmatically deformed, first, during Early Devonian under more brittle conditions at temperatures of 350-400 °C, whereas the Sunset Hills granite experienced more ductile deformation at temperatures of around 550 °C. 相似文献
19.
通过开展含预制单裂隙花岗岩的真三轴单面临空岩爆试验,并利用高速摄像系统和声发射（acoustic emission,简称AE）系统监测岩爆过程,探究了不同产状裂隙岩石的破坏模式、强度变形和声发射演化特性,分析了裂隙产状与岩爆过程及弹射动能之间的关系,对比了含裂隙岩石岩爆发生机制与无裂隙完整岩石的差异。有关力学特性的分析表明,随着裂隙倾角的减小,岩样破坏模式大体呈现由“内剪外劈”向“Z型斜剪”变化的趋势,裂隙对岩石强度的削弱作用不断增大。当裂隙倾角小于30°时,岩石峰值应力普遍仅为完整岩样的一半左右;小倾角裂隙的长度越大,岩样岩板劈裂现象变得显著,形成岩爆坑略微变大,且强度折减幅度越大,峰值轴向应变相应变小;裂隙位置向临空面靠近会加剧岩板的劈裂效应,塑性阶段普遍会产生较大变形并萌生大量裂纹,当裂隙已出露且切断临空面将不易形成岩爆坑。有关岩爆过程及弹射动能的分析表明,随着裂隙倾角的减小,岩样弹射动能呈现先显著降低后小幅回升的变化规律,30°倾角为转变拐点;岩样内部裂隙距临空面越近,裂隙岩样的弹射动能越小;树脂填充裂隙使得岩样弹射动能极大提升,而水泥填充的则无明显提升。有关声发射特征的分析表... 相似文献
20.
Manideepa Roy Choudhury Subhrajyoti Das Sadhana M Chatterjee Sudipta Sengupta 《Journal of Earth System Science》2016,125(5):1033-1040
Phulad Shear Zone (PSZ) of Delhi Fold Belt in Rajasthan is a northeasterly striking ductile shear zone with a well developed mylonitic foliation (035/70E) and a downdip stretching lineation. The deformation in the PSZ has developed in a transpressional regime with thrusting sense of movement. The northeastern unit, i.e., the hanging wall contains a variety of rocks namely calc-silicates, pelites and amphibolites and the southwestern unit, i.e., the footwall unit contains only granitic rocks. Systematic investigation of the granites of the southwestern unit indicate a gradual change in the intensity of deformation from a distance of about 1 km west of the shear zone to the shear zone proper. The granite changes from weakly deformed granite to a mylonite/ultramylonite as we proceed towards the PSZ. The weakly deformed granite shows a crude foliation with the same attitude of mylonitic foliation of the PSZ. Microscopic study reveals the incipient development of C and S fabric with angle between C and S varying from 15 ° to 24 °. The small angle between the C and S fabric in the least deformed granite variety indicates that the deformation has strong pure shear component. At a distance of about 1 m away from the PSZ, there is abrupt change in the intensity of deformation. The granite becomes intensely foliated with a strong downdip lineation and the rock becomes a true mylonite. In mesoscopic scale, the granite shows stretched porphyroclasts in both XZ and YZ sections indicating a flattening type of deformation. The angle between the C and S fabric is further reduced and finally becomes nearly parallel. In most places, S fabric is gradually replaced by C fabric. Calculation of sectional kinematic vorticity number ( Wn) from the protomylonitic and mylonite/ultramylonite granites varies from 0.3 ± 0.03 to 0.55 ± 0.04 indicating a strong component of pure shear. The similarity of the geometry of structures in the PSZ and the granites demonstrates that the deformation of the two units is broadly synchronous and the deformation in both the units is transpressional. 相似文献