亚干变质核杂岩的运动学涡度与剪切作用类型

运用极摩尔圆法、张量分析法和应力取向分析法对内蒙亚干变质核杂岩的剪切作用类型进行了定量分析。相关韧性剪切带的运动学涡度值为 0.53-0.87, 表明相关的剪切作用为减薄型一般剪切。其间的差异,表明主期以简单剪切为主,递进变形过程中, 纯剪切组分增加, 这很可能与因晚期脆性断层引起的位移分解作用有关。同向伸展褶劈理的取向与剪切带边界的夹角既不等于两流脊间的夹角,也不等于其值之半,但可据以确定主应力方向,从而确定两流脊间的夹角和对应的运动学涡度     

长乐-南澳断裂带晚中生代岩浆活动 与变质-变形关系

长乐-南澳断裂带是东南沿海地区陆内强烈变质-变形带。带内沉积岩、火山岩和早白垩世的钙碱性角闪石黑云花岗岩和花岗闪长岩都已发生可达角闪岩相的变质和石英-长石相韧性剪切变形。鉴于高温矿物和强烈韧性变形多出现在深成岩附近;远离深成岩,变质和变形就逐渐减弱,故本文认为,至少有一部分变质变形的热源是由岩浆提供的。韧剪组构和糜棱质花岗岩是在岩浆侵位的晚期或长乐-南澳断裂带左旋走滑时,在中地壳部位同时形成的,长乐断裂带中花岗岩的组构记录了一期同走滑变形的岩浆作用,“软变形”作用。据此,长乐-南澳带内花岗岩的形成是受走滑剪切应力和岩浆热双重制约的,是在走滑过程中实现的。其动力来源可能与晚中生代的太平洋板块沿日本中央构造线—台湾纵谷带朝东亚陆缘的斜向俯冲有关。     

锁儿头滑坡滑带土不同含水率大剪试验研究

锁儿头滑坡属特大型断层破碎带滑坡。该滑坡滑带土主要由强风化的中、上志留统千枚岩、板岩等构成,滑带土中粒径大于2 mm的颗粒含量约为30%,在滑带土颗粒组成中占有重要地位,其强度特征对滑坡体的稳定性分析具有重要影 响。为此,利用室内大型直剪仪对不同含水率下锁儿头滑坡滑带土的剪切特性进行试验研究,结果表明,在控制干密度为1.7 g/cm3情况下,不同含水率滑带土试样的剪应力-应变关系均呈现出弱应变硬化特征,而且法向压力越大,应变硬化特征越明显;在剪应变ε为10%时,相同含水率下滑带土剪切模量G0.1随法向压力的增大而增大,同一法向压力下的剪切模量G0.1与含水率间呈负线性相关关系;利用邓肯-张双曲线模型对锁儿头滑坡滑带土不同含水率下大剪试验剪应力-应变关系进行数据拟合,拟合效果良好,但该模型不能反映土的应变软化性质。     

节理分布位置对岩体剪切破裂特征影响试验研究

节理分布位置影响岩体综合抗剪强度,并控制“锁固段”型岩质边坡启动和破裂演化。通过模型试件剪切试验,分析了节理分布位置对岩体综合抗剪强度和破裂特征的影响程度。试件模型以水泥砂浆为材料,在剪切面不同位置预制封闭节理,使其成为四周密封、内部节理贯通的模型。在不同法向应力下进行剪切试验,测定综合抗剪强度变化规律和剪切破裂特征。试验结果表明:试样破裂面可分为翼部拉张区、翼部压剪区、端部拉张区三部分,各区面积所占比例随节理位置变化而波动。剪切强度参数也随节理位置变化而规律性波动,且法向应力越大,变化幅度越大。     

胶南隆起北缘中段左行正滑韧性剪切带研究

在详细的野外地质填图的基础上,通过各种尺度的构造研究和系统的应变测量,确定了胶南隆起北缘中段的大型左行正滑韧性剪切带的存在及其延展范围,并提出了确定韧性剪切带边界的构造几何学准则。研究了该韧性剪切带的几何学和运动学特征及变形机制,估算了其剪切位移量(大于7557m)及形成时的差异应力(σ_1-σ_3=94.6～114.4MPa)。该韧性剪切带可以作为胶南隆起的北部边界,但不是重要的板块碰撞边界。     

缓慢复活型滑坡滑带土的蠕变性质与特征强度试验研究

锁儿头滑坡是甘肃省舟曲县城附近、体积约72.85×106 m3的一个巨型老滑坡。20世纪70年代末滑坡开始复活,至今一直处于缓慢活动之中,显示滑坡活动具有典型的蠕动特点。滑带力学特性是控制滑坡活动机制的关键因素之一,为了弄清该滑坡滑带物质的蠕变性质以及控制滑坡活动的强度指标,通过滑带土残余状态下的直剪蠕变试验,研究了滑坡滑带土的蠕变特性,比较了滑带长期强度和残余强度的关系。研究发现,滑带土蠕变特性与应力状态相关,滑带进入加速蠕变的临界剪应力和剪切速率均与正应力线性正相关。该滑坡应力状态指示其已具备进入加速蠕变的条件。残余状态下该滑坡滑带土的长期与残余强度基本等价,前者略大于后者,且增大量值与正应力有负相关关系。     

新疆胜利达坂金矿区金矿化特征

胜利达坂金矿区,发育近EW向的韧性剪切带。该剪切带是区内金矿的主要控矿构造,控制了矿床、矿体及矿化体的分布。矿体主要沿韧性剪切带糜棱面理分布。矿石的主要类型是浸染糜棱岩型和变形石英脉型。成矿的最有利部位是剪切带内应力梯度大的地带。区内乳白色变形石英脉具有很大的找金潜力。该区金矿属韧性剪切带型金矿。     

How did the foreland react? Yangtze foreland fold-and-thrust belt deformation related to exhumation of the Dabie Shan ultrahigh-pressure continental crust (eastern China)

During the Triassic collision of the Yangtze and Sino-Korean cratons, the leading edge of the Yangtze crust subducted to mantle depths and was subsequently exhumed as a penetratively deformed, coherent slab capped by a normal shear zone. This geometry requires a reverse shear zone at the base of the slab, and we suggest that the Yangtze foreland fold-and-thrust belt constitutes this zone. Lower Triassic rocks of the eastern foreland record NW–SE compression as the oldest compressional stress field; onset of related deformation is indicated by Middle Triassic clastic sedimentation. Subsequent Jurassic stress fields show a clockwise change of compression directions. Based on nearly coeval onset and termination of deformation, and on a common clockwise change in the principal strain/stress directions, we propose that the foreland deformation was controlled by the extrusion of the ultra high-pressure slab. Widespread Cretaceous–Cenozoic reactivation occurred under regional extension to transtension, which characteristically shows a large-scale clockwise change of the principal extension directions during the Lower Cretaceous.     

DEM Simulation of Direct Shear: 2. Grain Boundary and Mineral Grain Strength Component Influence on Shear Rupture

The influence of mineral grain and grain boundary strength is investigated using a calibrated intact (non-jointed) brittle rock specimen subjected to direct shear with a particle-based distinct element method and its embedded grain-based method. The adopted numerical approach allows one to independently control the grain boundary and mineral grain strength. The investigation reveals that, in direct shear, the normal stress (σ _n) applied to a rock specimen relative to its uniaxial compressive strength (UCS) determines the resulting rupture mechanism, the ultimate rupture zone geometry, and thus its shear stress versus horizontal displacement response. This allows one to develop a rupture matrix based on this controlling parameter (i.e., σ _n/UCS). Mineral grain strength reductions result in the lowering of the apparent cohesion intercept of the peak linear Coulomb strength envelope, while grain boundary strength reductions change the peak linear Coulomb strength envelope to a bi-linear or curved shape. The impact of grain boundary strength is only relevant at σ _n/UCS ratios <0.17 where tensile and dilatant rupture mechanisms dominate. Once shear rupture begins to be the dominant rupture mechanism in a brittle rock (i.e., at σ _n/UCS ratios >0.17), the influence of weakened grain boundaries is minimized and strength is controlled by that of the mineral grains.     

基于三维扫描和三维雕刻技术的岩石结构面原状重构方法及其力学特性

为了客观重复制作与原岩结构面的岩性、表面形态和力学性质完全一致的试样,集成三维扫描和三维雕刻技术,提出了原岩结构面试样重构新方法。采用该方法制作了具有相同表面形态的大理岩结构面试样,开展了不同法向力下的直剪试验,并采用声发射技术对结构面剪切破坏过程进行了监测。结果表明：重构结构面试样与原始结构面试样具有高度相似性;结构面剪应力-剪切位移曲线可分为两类：剪胀滑移型和剪断跌落型;剪切破坏后结构面可明显地划分为两个区域：剪胀脱开区和剪断磨损区;提出了结构面剪切强度新公式,理论公式与试验结果更接近;结构面剪切过程中剪应力、能量率、计数、撞击率随时间的变化规律具有较好的一致性,声发射定位位置与剪切过程中结构面损伤破坏区域基本吻合。     

江西武功山东区大型韧性剪切带的显微构造特征

武功山东区存在一条大型韧性剪切带。鞘褶皱倒向以及旋转变形构造(如S-C面理组构、旋转碎斑系、雪球构造和粒内显微破裂构造等)显示此剪切带为由南向北逆冲推覆性质。砾石、黄铁矿还原斑和石英斑晶的有限应变分析表明剪切带西段和东段岩石分别以收缩型椭球和压扁型椭球变形为特征。剪切带的主要变形时代是早古生代,可能与早古生代华夏陆块和扬子陆块之间的碰撞造山作用有关。     

皖南某高速公路强风化千枚质板岩边坡变形特征及稳定性分析

以皖南地区某强烈变形的强风化千枚质板岩边坡为例,通过对其工程地质条件的调查,结合边坡岩体结构类型和结构面组合特征,对其变形破坏特征及稳定性进行了分析和评价。研究结果表明,边坡的变形受坡内软弱岩体(挤压破碎带)控制,剪应力的集中易使坡体产生圆弧形滑动,据此定量评价边坡的稳定性,提出合理的支护方案,减小地质灾害发生的可能。     

Volume strain, strain type and flow path in a narrow shear zone

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 R_f/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.     

Localization patterns in sandbox-scale numerical experiments above a normal fault in basement

The finite element program ELFEN is used to study the effect of basement fault dip on the evolution of shear band patterns in unconsolidated sand. The material properties and boundary conditions of the model were chosen to correspond to generic sandbox experiments.Model results reproduce the range of structural styles found in corresponding sandbox experiments. With a basement fault dip of 60° and lower, a graben structure is formed, composed of a synthetic shear band followed by one or more antithetic shear bands. With a basement fault dip of 70° and steeper, a reverse (precursor) shear band forms first, followed by a synthetic, normal shear band that accommodates all further displacement. The dip of the synthetic shear band is close to the basement fault dip. For basement fault dips between 60° and 70°, we observe a transition in localization patterns. An analysis of the stress fields and velocity vectors in the model explains the first-order aspects of the relationships observed.We consider the observed ‘precursor-dominated’ and ‘graben-dominated’ structural domains to be important components of normal fault systems in which the first order structural style and deformation patterns are only weakly dependent on the details of the rheology of the model materials and explore the interesting problem of the change in structural style from ‘precursor-dominated’ to ‘graben-dominated’ structural domains above a normal fault in basement. We find similar structural domains in sandbox experiments for the same set of boundary conditions but with slightly different material properties, suggesting that the modeled patterns are robust within these two structural domains, (i.e. will occur over a range of similar material properties and boundary conditions).The results of this study contribute to our ability to validate numerical models against experiments in order to finally better simulate natural systems.     

Structure and geochronology of the Tongbai complex and their implications for the evolution of the Tongbai orogenic belt,central China

The Tongbai orogenic belt has an overall antiformal geometry and the hinge of the antiform is sub-horizontal and trends NW–SE. The Tongbai complex (TBC) in the core of the antiform is bounded by the S-dipping Yindian–Malong shear zone in the south, the sub-horizontal Taibaiding shear zone at the top and the N-dipping Hongyihe–Tongbai shear zone in the north. The three shear zones have dextral, top-to-NW and sinistral movement, respectively. They are parts of a single shear zone, termed the Tongbai shear zone, that has a uniform top-to-NW sense of shear. Three samples of deformed granitoid (mylonite or protomylonite) from the shear zone have U–Pb zircon ages of 145 ± 6 Ma, 142 ± 2 Ma and 131 ± 6 Ma, respectively. An L-tectonite in the TBC yielded a metamorphic age of 137 ± 8 Ma and a migmatite an age of 137 ± 1 Ma. The Tongbai shear zone is intruded by undeformed Early Cretaceous granite and dykes and deformation in the shear zone is constrained to ca. 140–135 Ma, synchronous with metamorphism and migmatization in the TBC. Early Cretaceous magma emplacement and the associated uplift modified the TBC into a gentle antiform and the uplift may have continued to ca. 102–85 Ma. Similar geometry and kinematics have been documented in the Dabie orogenic belt to the east, which suggests that the Central Orogenic Belt in China probably experienced a uniform orogen-parallel extension and top-to-NW shearing in the ductile lithosphere in the Early Cretaceous.     

The deformation of overburden soil induced by thrust faulting and its impact on underground tunnels

Overburden soil beds situated above a fault are often deformed by propagation of bedrock thrusting from the fault during large earthquake. The deformed beds formed a triangular shear zone. This coseismic faulting often causes damage to underground tunnels located in the shear zone. The present research studies the deformation behavior of the overburden soil beds and the tunnel, the associated mechanism and the impact on the safety of tunnel linings induced by a large blind thrust slip. Based on sandbox experimental and numerical studies, it is found that results from numerical analysis are in agreement with the sandbox model tests with regard to growths of the shear zones within the soil beds, location of the tunnel in this shear zone and deformations of the tunnel. The potential major shear zone may be bent or bifurcated into two sub-shear zones owing to existence of a tunnel inside the shear zone. Furthermore, the occurrence of back-thrust faulting will threaten the safety of nearby structures. It was also identified that stiffness of the soil and the fault dip angles are among the major factors controlling the configuration of shear zones, the stresses within the soil, and the loads on tunnel linings. Based on the identified mechanisms, the strategies for hazard prevention are accordingly suggested and discussed.     

Grain and sub-grain size variations across a mylonite zone

The results are reported of a combined optical and electron microscopy study of microstructural variations across a quartz mylonite zone with increasing shear strain. The mylonite developed by recrystallization of the deformed quartz grains with increasing shear strain. It was found in a given specimen that the size of recrystallized grains and of sub-grains were always smaller in electron micrographs. The possible reasons for this are discussed. The size of both features decreased with increasing shear strain irrespective of the microscope used. However the density of unbound dislocations remained constant. A marked grain size reduction occurred in phyllosilicate rich layers. Variations in sub-grain size were observed within the relict old grains which remained at low shear strains. These are thought to reflect stress intensification adjacent to grain boundaries during deformation. The relict grains recrystallized at higher strains. Stresses were estimated from grain and sub-grain sizes and from the dislocation density. The results indicate that estimates based on grain size are unreliable if phyllosilicates inhibit the growth of grains during recrystallization, and that the dislocation densities are altered during uplift and are unlikely to give meaningful estimates. It is also concluded that the microstructures reflect stress gradients present during the formation of the mylonite, that is the initiation and propagation of the shear zone and that these were subsequently replaced by strain rate gradients.     

Removal of finite deformation using strain trajectories

A technique is described for removing the effects of finite deformation, given the principal values and orientations of strain at a number of points throughout a deformed body.Using the principal orientations, strain trajectories are constructed for the deformed state. The body is divided into finite elements bounded by these trajectories. Each element is then unstrained without changing its orientation or position. This process creates artificial voids and overlaps, which are minimized by imparting rigid translations and rotations to the elements according to a least squares method.The result is the pattern of strain trajectories for the undeformed state. It is shown that the trajectories for the deformed and undeformed states may be used as reference coordinates in order to map the change in shape of any body as it passes from the deformed to the undeformed state or vice versa. The technique is tested using models of a folded layer and a shear zone. It is suggested that the technique is versatile enough to allow for errors in original strain data. Although the technique has so far been applied to two-dimensional deformations, a similar method should be usable in three dimensions.     

云蒙山变质核杂岩抬升过程中伸展拆离和岩浆底辟联合作用的证据

北京地区云蒙山变质核杂岩在白垩纪阶段抬升的早期,伴随着沿四合堂剪切带由北向南的拆离滑脱和大型花岗闪长岩的垂向侵位,晚期变形发生在花岗闪长岩岩基周边及其邻近围岩中,形成云蒙山剪切带,并伴随大量同构造的花岗岩和伟晶岩岩脉灌入。剪切带中所有的岩脉都随时间发生了不同程度的变形,较老的岩脉形成紧闭的圆柱状褶皱,枢纽与剪切带的线理和面理接近平行。岩脉与剪切带中L-S组构的平行化作用主要是由于这种转动的结果。岩脉的成分和长英指数随它们的变形程度发生变化,说明持续的岩浆分异作用与韧性剪切变形是同时发生的。云蒙山剪切带由岩浆底辟引起的上盘岩石重力所驱动,并不断得到同构造侵位岩脉的补充,起到存储和不断改造侵位岩脉的作用。早期伸展体制下形成的四合堂剪切带局部遭受云蒙山剪切带的改造或复合。该地区的岩石、构造和同构造岩脉的变形几何学和运动学证据表明,太古宙结晶基底的抬升是下部岩浆底辟与上部地壳伸展拆离共同作用的结果。     

长乐—南澳断裂带东山段剪切变形与剪切加热作用

本文在系统的有限应变测量的基础上,对闽东南长乐—南澳断裂带东山段剪切变形特征进行了分析:利用变形石英显微亚结构。(动态重结晶颗粒)估算了剪切带内古应力并(σ—σ_3):通过对剪切变形能密度分布W(x)格离散化计算,采用有限差分数值近方法,获得了剪切热数值解:最后总结了研究地区剪切变形,剪切加热与动热成岩成矿作用的相对时空关系以及长乐—南澳断裂域构造意义