岩石磁组构在断裂变形性状与期次研究中的应用——以广西博白-合浦断裂为例

岩石磁化率椭球体的三个轴与应变椭球体的三个轴方向相平行,并具有一定的共构关系.变形岩石的磁组构参数P、T、F、L以及磁化率椭球体主张量方向等可以用来定量地表征岩石变形的性状及期次.本文通过实测和计算27个样品的磁组构参数,研究了博白-合浦断裂带的变形性状与期次,结果表明:博白-合浦断裂带大致经历了三期构造变形作用,不同时期具不同性质的构造变形.变形性状分别表现为韧性、韧-脆性及脆性变形,应变行为分别表现为平面、非平面和线性应变.     

剪切带研究现状及内容

“剪切带”(Shear Zone)是用来泛指地壳内窄的为近于平行的边界所限制的高应变带,大到板块间的俯冲带,小到手标本中的小型剪切带。按其变形方式可分为:脆性剪切带——断层,脆性和韧性过渡的剪切带,韧性剪切带。它们反映了不同层次(深度)的构造变形。弥剪切带(一般指韧性剪切带及部分过渡性剪切带)的研究,从七十年代以来有了很大的发     

对磁组构在岩石变形分析应用中若干问题的思考

在应用传统的磁组构方法进行岩石构造变形分析时,发现这些方法中有许多不完善之处,如变形岩石磁化率量值椭球和应变椭球是否可以对应及对应条件,初始磁组构是否会影响变形碉石磁化率量值椭球与应变椭球的对应关系,岩石脆性破裂前的塑性变形是否影响磁组构,韧性变形如何影响磁组构,能否用磁组构来推断主应力方向,Ｒａｔｏｒｅ（１９８０）最小磁化率指向对韧性剪切带运动方向和方式的分析在多期变形区是否适用等,并据此提出解     

衡山岩体西缘韧性剪切带磁性组构研究

本文对采自衡山花岗岩体西缘韧性剪切带的标本进行了岩石磁性组构研究,并将其与常规应变分析方法所得结果予以比较,表明了岩石磁化率各向异性椭球体与应变椭球体之间有一定的对应关系,岩石磁化率各向异性技术可望成为构造地质学的一种新手段。岩石磁性组构资料可应用于变形岩石的应变分析,特别是在没有宏观应变标志或者通常的岩石组构分析方法太费时间的情况下更显出其优越性。     

闽—粤东南沿海大陆边缘韧性剪切带的基本特征

东南沿海大陆边缘剪切带是西太平洋活动大陆边缘构造带的组成部分,它是一条具有多次活动的左旋韧性平移剪切带。在本剪切带中可以观察到3种类型的构造:（1）规模巨大的呈北北东—北东向展布的糜棱岩带以及山拉伸线理组成的线状构造带。它们在平面上有明显的从断目两侧向中心递进变形特征;（2）呈北东走向陡倾角的糜棱叶理（Sa）、应变滑劈理或破劈理（Sb）、小型剪切带（Sc）;（3）由西到东断层作用样式和断层岩具有明显的递进变化特点。西部（浅部）断层作用以脆性剪切滑动为主,其断层岩则由假玄武玻璃及镜面糜棱岩组成;中部断层作用以跪—韧性剪切为主,为断层泥—碎裂岩—超碎裂岩;东部(深部,以韧性剪切作用为主,其断层岩为暖棱岩—花岗糜桂片麻岩—眼球状糜棱岩系列。以上特点表明在本剪切带内透入性和非透入性变形之间有着密切的关系,反映出在变形过程中具有由韧性变形逐渐向脆性变形的发展趋势。     

材料缺陷对岩样变形局部化影响的数值模拟

在平面应变压缩条件下,采用拉格朗日元法研究了材料缺陷对岩样应变局部化及宏观力学行为的影响。在数值计算中,采用了莫尔-库仑与拉破坏复合的破坏准则,峰后岩石的本构关系为线性应变软化。对于理想岩样（不含任何缺陷）,从剪切应变率的等值线图及变形网格图发现,变形场相对试样垂直对称轴对称。在试样的边界上设置材料缺陷后,变形场的对称性被打破。材料缺陷附近是局部化现象启动的主要位置。与不含材料缺陷试样相比,含缺陷试样的局部化提前启动。当缺陷位于试样左边界中部附近时,试样内部出现多条剪切带,发生韧性剪切破坏,峰后应力-轴向应变曲线和应力-侧向应变曲线均倾向于韧性,岩样的稳定性增强;当缺陷位于试样上、下端面附近时,仅出现一条贯穿试样左右边界的剪切带,发生脆性剪切破坏,峰后两种曲线倾向于脆性,易发生失稳破坏。从数值结果中还观测到了剪切带的跳跃或迁移现象及剪切带的相互竞争、此消彼涨的现象。当岩样中不包含任何缺陷时,试样应力-变形曲线的峰值强度最高。随着缺陷的上移,峰值强度下降,直到峰值强度基本保持不变。缺陷越接近于岩样的下端,对岩样应力-变形曲线的峰值强度的影响越小。     

考虑塑性应变率梯度的单轴压缩岩样轴向响应

基于剪切应变率梯度格式,采用解析方式研究了岩石材料在单轴压缩条件下的应变软化的结构响应。根据非局部连续介质模型,提出了一维二阶剪切应变率梯度格式。非局部剪切应变率与局部剪切应变率及其二阶梯度有关。将经典塑性理论中的局部剪切应变率替换为非局部剪切应变率,可以直接得到局部剪切应变率的封闭解析解,而不必通过将局部剪切应变对时间求导获得。通过对局部剪切应变率积分,得到了沿剪切带方向的相对剪切速度。试件峰值强度后的端部速度由弹性及塑性两部分构成。前一部分由虎克定律描述;后一部分与相对剪切速度有关。对弹性及塑性两部分速度求和,得到了单轴压缩岩样剪切破坏问题轴向响应的解析式。研究表明：试样高度越大、内部长度越小、剪切软化模量越大及泊松比越小,则岩样的轴向响应倾向于脆性。根据岩样与矿柱的相似性,岩样响应倾向于脆性,意味着矿柱将失去稳定性,发生矿柱岩爆。目前的基于剪切应变率梯度格式的主要优点是简洁。     

有限应变测量的关键原理——摩尔圆

20世纪60年代,在板块理论建立的同时,对变形岩石和矿田构造作定量分析以替代定性分析的有限应变测量方法也建立了起来。定量分析的主要标志是将摩尔圆方法从力学引入到地质学,同时也引入矿田构造分析中,并且得到改进与发展。有限应变摩尔圆为分析岩石大变形而建立,极摩尔圆随后为分析广布于野外岩石中的一般剪切变形而建立。我国著名学者李四光在此之前将应力摩尔圆和库仑准则从力学领域介绍到构造地质学,尔后一些中国学者为改进和发展极摩尔圆方法作出了自己的贡献。本文以浅显的方式解释摩尔圆的基本概念和作图方法,附带做些练习和解答。     

一种模拟韧性剪切带中椭球状标志体运动、变形的新方法

韧性剪切带中赋存的椭球状应变标志体(砾石、碎斑等)是研究剪切带运动学、动力学的重要应变标志体。传统研究中椭球状标志体通过对野外露头的观测或与实验岩石学结合,判断剪切带运动方向、探讨运动学和流变学特征。随着数值模拟技术在韧性剪切带中的引入和推广,国内外许多学者试图恢复椭球状标志体的运动轨迹和变形特征,并取得了显著的成果。然而,国内文献对于模拟韧性剪切带椭球状标志体的定量及模拟研究甚少,研究方法也鲜为介绍。基于此,针对韧性剪切带中椭球状标志体变形的最新研究进展,详细介绍建立在Jeffery理论和Eshelby理论之上的数值模拟思路和方法,并利用Mathcad软件模拟了给定条件下的椭球状标志体的运动轨迹、变形特征。     

韧性剪切带及其控矿作用——以新疆康古尔金矿为例

康古尔金矿具有独特的成矿地质特征,矿床位于石炭系火山岩区大型韧性剪切带的次级构造中.控矿构造表现为脆韧性剪切活动的特点,该脆韧性剪切带在成矿期的活动具有中低温、高应变速率、高差异应力的动力学特征.金矿床的分布受脆韧性剪切带控制,矿体由蚀变千糜岩和糜棱岩化火山岩中矿化富集地段组成,矿体产状平行于糜棱岩面理.矿化产于脆韧性变形强烈部位,脆性变形叠加有利于形成富金矿.     

Deformation Localization-A Review on the Maximum- Effective-Moment (MEM) Criterion

The essential difference in the formation of conjugate shear zones in brittle and ductile deformation is that the intersection angle between brittle conjugate faults in the contractional quadrants is acute(usually ~60°) whereas the angle between conjugate ductile shear zones is obtuse(usually 110°). The Mohr-Coulomb failure criterion, an experimentally validated empirical relationship, is commonly applied for interpreting the stress directions based on the orientation of the brittle shear fractures. However, the Mohr-Coulomb failure criterion fails to explain the formation of the low-angle normal fault, high-angle reverse fault, and the conjugate strike-slip fault with an obtuse angle in the σ1 direction. Although it is ten years since the Maximum-Effective-Moment(MEM) criterion was first proposed, and increasingly solid evidence in support of it has been obtained from both observed examples in nature and laboratory experiments, it is not yet a commonly accepted model to use to interpret these antiMohr-Coulomb features that are widely observed in the natural world. The deformational behavior of rock depends on its intrinsic mechanical properties and external factors such as applied stresses, strain rates, and temperature conditions related to crustal depths. The occurrence of conjugate shear features with obtuse angles of ~110° in the contractional direction on different scales and at different crustal levels are consistent with the prediction of the MEM criterion, therefore ~110° is a reliable indicator for deformation localization that occurred at medium-low strain rates at any crustal levels. Since the strain–rate is variable through time in nature, brittle, ductile, and plastic features may appear within the same rock.     

鲁西地区韧性剪切带岩石磁组构分析及其构造意义

岩石磁组构分析可用来研究岩石的组构特征及构造变形。鲁西地区韧性剪切带岩石磁组构具有磁各异性度Ｐ和磁百分率各向异性值Ｈ高、磁化率量值椭球呈压扁状、磁面理发育而磁线理不发育的特点。区内韧性剪切带变形强烈,以压扁作用为主,最大主压应力方向近ＮＥ和Ｓ－Ｎ向,以右旋运动为主。韧性剪切带形成以后,区内主要经历了热蚀变和脆性变形,韧性变形很弱     

西藏罗布莎豆荚状铬铁矿成矿演化的构造过程

摘要：通过对罗布莎铬铁矿区的构造解析,揭示出了豆荚状铬铁矿的成矿演化规律。由地幔韧性剪切带和脆－韧性剪切带组成的含铬剪切带是成矿期构造,被造山期发生的变形分解作用和脆性断裂作用改造,成矿演化经历了从上地幔到上地壳所发生的５个构造变形相的转换,即熔融流变变形相→地幔韧性剪切变形相→壳幔脆→韧性剪切变形相→塑性挤压变形相→脆性断裂变形相,可划分为中生代改造成矿和新生代矿床改造两个阶段,并概括为包含６个变形世代的构造成矿序列。     

On the petrology of brittle precursors of shear zones – An expression of concomitant brittle deformation and fluid–rock interactions in the ‘ductile’ continental crust?

The inherited localization model for shear zone development suggests that ductile deformation in the middle and lower continental crust is localized on mechanical anisotropies, like fractures, referred to as shear zone brittle precursors. In the Neves area (Western Tauern Window, Eastern Alps), although the structural control of these brittle precursors on ductile strain localization is well established, the relative timing of the brittle deformation and associated localized fluid flow with respect to ductile deformation remains in most cases a matter of debate. The present petrological study, carried out on a brittle precursor of a shear zone affecting the Neves metagranodiorite, aims to determine whether brittle and ductile deformations are concomitant and therefore relate to the same tectonic event. The brittle precursor consists of a 100–500 µm wide recrystallized zone with a host mineral‐controlled stable mineral assemblage composed of plagioclase–garnet–quartz–biotite–zoisite±white mica±pyrite. Plagioclase and garnet preserve an internal compositional zoning interpreted as the fingerprint of Alpine metamorphism and fluid–rock interactions concomitant with the brittle deformation. Phase equilibrium modelling of this garnet‐bearing brittle precursor shows that metamorphic garnet and plagioclase both nucleated at 0.6 ± 0.05 GPa, 500 ± 20°C and then grew along a prograde path to 0.75 ± 0.05 GPa, 530 ± 20°C. These amphibolite facies conditions are similar to those inferred from ductile shear zones from the same area, suggesting that both brittle and ductile deformation were active in the ductile realm above 500°C for a depth range between 17 and 21 km. We speculate that the Neves area fulfils most of the required conditions to have hosted slow earthquakes during Alpine continental collision, that is, coupled frictional and viscous deformation under high‐fluid pressure conditions ~450°C. Further investigation of this potential geological record is required to demonstrate that slow earthquakes may not be restricted to subduction zones but are also very likely to occur in modern continental collision settings.     

Damage formation associated with bending under a constant moment

Deformation within the Earth's lithosphere is largely controlled by the rheology of the rock. Fracture and faulting are characterized by elastic rheologies with brittle mechanisms, while folding and flow are characterized by plastic and/or viscous rheologies due to ductile mechanisms. However, it has been recognized that deformation that resembles ductile behavior can be produced within the confines of the brittle lithosphere. Specific examples are folds that form in the shallow crust, steep hinges at subduction zones that are accompanied by seismicity, and large-scale deformation at plate boundaries. In these cases, the brittle lithosphere behaves elastically with fracture and faulting yet produces ductile behavior. In this paper, we attempt to simulate such ductile behavior in elastic materials using continuum damage mechanics. Engineers utilize damage mechanics to model the continuum deformation of brittle materials. We utilize a modified form of damage mechanics that represents a reduction in frictional strength of preexisting fractures and faults. We use this empirical approach to simulate the bending of the lithosphere under the application of a constant moment.We use numerical simulations to obtain elastostatic solutions for plate bending and where the longitudinal stress at a particular node exceeds a yield stress, we apply damage to reduce Young's modulus at the node. Damage is calculated at each time step by a power-law relationship of the ratio of the yield stress to the longitudinal stress and the yield strain to the longitudinal strain. This results in the relaxation of the material due to increasing damage. To test our method, we apply our damage rheology to an infinite plate deforming under a constant bending moment. We simulate a wide range of behaviors from slow relaxation to instantaneous failure, over timescales that span six orders of magnitude. Using this method, stress relaxation produces elastic-perfectly plastic behavior in cases where failure does not occur. For cases of failure, we observe a rapid increase in damage leading to failure, analogous to the acceleration of microcrack formation and acoustic emissions prior to failure. The changes in the rate of damage accumulation in failure cases are similar to the changes in b-values of acoustic emissions observed in triaxial compression tests of fractured rock and b-value changes prior to some large earthquakes. Thus continuum damage mechanics can simulate the phenomenon of ductile behavior due to brittle mechanisms as well as observations of laboratory experiments and seismicity.     

Deformation Characters of the Maowen Fault Belt in Longmenshan, Western Sichuan

1. Introduction The Longmenshan orogenic belt is a typical intercontinental orogenic belt (Fig. 1), from NW to SE composed of Paleozoic epimetamorphic rock systems, Protozoic intermediate-acid intrusions and metamorphic rocks (called Pengguan Complex), Upper Triassic sandshales, and Paleozoic glided nappe as well as Jurassic-Tertiary molass formation,. The Maowen fault belt is a boundary fault belt between the Longmenshan orogenic belt and Songpan-Garze fold belt. It starts from Shenx…     

Deformation conditions, kinematics, and displacement history of shallow crustal ductile shearing in the Norumbega fault system in the Northern Appalachians, eastern Maine

The Norumbega fault system in the Northern Appalachians in eastern Maine experienced complex post-Acadian ductile and brittle deformation from middle through late Paleozoic times. Well-preserved epizonal ductile shear zones in Fredericton belt metasedimentary rocks and granitic batholiths that intrude them provide valuable information on the nature, geometry, and evolution of orogen-parallel strike-slip Norumbega faulting. Metasedimentary rocks were ductilely sheared into phyllonite schistose mylonite, whereas granite into mylonite within the ductile shear zones. Ductile shearing took place at conditions of the lower greenschist facies with peak temperatures on the order of 300–350° based on comparison of plastic quartz and brittle feldspar microstructures, confirming a shallow crustal environment during faulting.Ductile shear strain was partitioned into two major shear zones in easternmost Maine—the Waite and Kellyland zones—but these zones converge toward the southwest. Megascopic, mesoscopic, and microscopic kinematic indicators confirm that fault motion in both zones was dominantly dextral strike-slip. Detailed mapping, especially in the plutonic rocks, reveals a complex ductile deformation history in the area where the Waite and Kellyland zones converge. Shear strain is broadly distributed in the rocks between Kellyland and Waite zones, and increases toward their junction. Multiple dextral high-strain zones oblique to both zones resemble megascopic synthetic c′ shear bands. Together with the Kellyland and Waite master shear zones, these define a megascopic S–C′ structure system produced in a regional-scale dextral strike-slip shear duplex that developed in the transition zone between the deeper (south-central Maine) and shallower (eastern Maine) segments of the Norumbega fault system.Granite plutons caught within the strike-slip shear duplex were intensely sheared and progressively smeared into long and narrow slivers identified by this study. The western lobe of the Deblois pluton and the Lucerne pluton have been recognized as the sources, respectively of the Third Lake Ridge and Morrison Ridge granite slivers. Restoration of both granite slivers to their presumed original positions yields approximately 25 km of dextral strike-slip displacement along only the Kellyland and synthetic ductile shear zones.     

超高压变质岩的塑性流变：显微构造和变形机制

超高压变质岩是大陆深俯冲作用的产物。超高压变质岩在深俯冲和快速折返过程中,经历了长距离地构造搬运和构造力的作用。其构造变形主要集中在韧性剪切带中,并发生强烈地塑性流变。研究超高压变质构造岩的显微构造及其变形机制对于深入了解大陆壳岩石在深俯冲过程中的流变学行为有十分重要的意义,山东仰口的超高压韧性剪切带中榴辉岩质和花岗质糜棱岩记录了超高压变形的历史。在超高压条件下的稳定矿物绿辉石、多硅白云母、兰晶石和钾长石具有不规则波状消光、亚晶界、核幔构造和动态重结晶等显微构造特征,TEM 研究揭示了大量的位错构造,表明位错蠕变是其主要的变形机制。在花岗质糜棱岩中,金红石在刚性矿物的压力影中沉积,细粒的石榴石条带平行片理延伸,都说明超高压变形过程中有流体存在,流体助力的物质扩散迁移是又一个重要的变形机制。依据现有的流变学定律估算的流变应力应该在几十兆帕以上。     

韧性剪切带型金矿三阶段构造成矿模式——以广东河台金矿床为例

基于对粤西河台韧性剪切带型金矿的构造解析,本文提出了韧性剪切带型金矿成矿的一种新构造模式,即:在大型韧性剪切带运动指向的前锋,当扩展弱化而出现分支糜棱岩带时,就会在韧性剪切带中出现由强变形带包绕的构造透镜体弱变形域。由于透镜体域中央岩石处于脆性环境,在变形分解过程中,强变形带中含金流体会通过岩石中的微破裂渗透到相对低压的弱变形构造透镜体域中央,并通过构造泵吸机制在其中产生周期性的液压致裂与裂开‒愈合,这为在韧性剪切阶段活动的金提供了一个理想的沉淀场所。上述构造机制很好地解释了河台金矿床中透镜状特富矿体的成因。河台含金韧性剪切带在韧性、韧‒脆性及脆性阶段在同位空间并列与叠加了不同类型金矿体,从早到晚分别形成细脉‒浸染型、石英脉型与破碎带蚀变岩型金矿体。河台韧性剪切带群为粤西深层次逆冲推覆构造前缘陡坡带的分支糜棱岩带,其韧性剪切阶段为左旋平‒逆剪切,韧‒脆性与脆性阶段转变为右旋平‒逆剪切,并依此讨论了金矿体的侧伏规律及隐伏矿体的预测方向。