甘肃安西县寒山金矿床控矿因素及找矿方向

寒山金矿位于甘肃北祁连造山带西段、阿尔金大断裂带南侧.矿床受控于由阿尔金大断裂派生的北西向韧脆性剪切带中.文章从成矿地质条件、矿床地质特征等入手,分析了矿床的控矿因素,认为该矿床受含矿地层、韧脆性剪切带构造、岩浆岩等因素的制约.提出了新的找矿方向,认为韧脆性剪切带中的次级断层和矿体深部勘探,是该矿床今后找矿的重要方向.     

Surface roughness evolution on experimentally simulated faults

To investigate the physical processes operating in active fault zones, we conduct analogue laboratory experiments where we track the morphological and mechanical evolution of an interface during slip. Our laboratory friction experiments consist of a halite (NaCl) slider held under constant normal load that is dragged across a coarse sandpaper substrate. This set-up is a surrogate for a fault surface, where brittle and plastic deformation mechanisms operate simultaneously during sliding. Surface morphology evolution, frictional resistance and infra-red emission are recorded with cumulative slip. After experiments, we characterize the roughness developed on slid surfaces, to nanometer resolution, using white light interferometry. We directly observe the formation of deformation features, such as slip parallel linear striations, as well as deformation products or gouge. The striations are often associated with marginal ridges of positive relief suggesting sideways transport of gouge products in the plane of the slip surface in a snow-plough-like fashion. Deeper striations are commonly bounded by triangular brittle fractures that fragment the salt surface and efficiently generate a breccia or gouge. Experiments with an abundance of gouge at the sliding interface have reduced shear resistance compared to bare surfaces and we show that friction is reduced with cumulative slip as gouge accumulates from initially bare surfaces. The relative importance of these deformation mechanisms may influence gouge production rate, fault surface roughness evolution, as well as mechanical behavior. Finally, our experimental results are linked to Nature by comparing the experimental surfaces to an actual fault surface, whose striated morphology has been characterized to centimeter resolution using a laser scanner. It is observed that both the stress field and the energy dissipation are heterogeneous at all scales during the maturation of the interface with cumulative slip. Importantly, we show that the formation of striations on fault planes by mechanical abrasion involves transport of gouge products in the fault plane not only along the slip direction, but also perpendicular to it.     

Improved Geometric Model of Extensional Fault–bend Folding

Extensional fault–bend folds, also called rollovers, are one of the most common structures in extensional settings. Numerous studies have shown that oblique simple shear is the most appropriate mechanism for quantitative modeling of geometric relations between normal faults and the strata in their hanging walls. However, the oblique simple shear has a rather serious issue derived from the shear direction, particularly above convex bends. We use geometric and experimental methods to study the deformation of extensional fault–bend folds on convex bends. The results indicate that whether the fault bends are concave or convex, the shear direction of the hanging wall dips toward the main fault. On this basis, we improve the previous geometric model by changing the shear direction above the convex bends. To illustrate basin history, our model highlights the importance of the outer limit of folding instead of the growth axial. Moreover, we propose a new expression for the expansion index that is applicable to the condition of no deposition on the footwall. This model is validated by modeling a natural structure of the East China Sea Basin.     

Numerical analysis of overburden soil subjected to strike-slip fault: Distinct element analysis of Nojima fault

A distinct element method analysis is carried out to examine the development of shear bands in overburden soil subjected to a strike-slip fault. About 2.3 million spherical particles are used in the analysis and the results are compared with the shears observed at the Nojima earthquake fault during the 1995 Hyogoken Nanbu earthquake. En echelon shears and secondary shears which strike at lower angles to the basement fault – typical in strike-slip faults – are observed in the numerical analysis. Simple shear in the horizontal plane and drag due to the dependence of velocity on depth are confirmed to control the helicoidal shape of Riedel shears. Rotation of the compressional direction toward the fault strike as a result of slip along Riedel shears is also verified. It is found that the compressional direction is more horizontal within the area enclosed by Riedel shears than in outside areas and that these compressional directions produce secondary lower-angle shears that are less helicoidal. It is shown that the formation of column-like structures of particles and their subsequent buckling play significant micromechanical roles in three-dimensionally wrenched shears. The results of the numerical analysis, such as shear intervals and striking angles, show a resemblance to observational results at sites where sediment contains coarse grains and is subjected to strike slip with a small dip component, although they are not exactly the same as those observed at locations with similar overburden thicknesses.     

大兴断层的三维几何学与运动学及其对廊固凹陷成因机制的约束

大兴断层是位于渤海湾盆地冀中坳陷西北部的廊固凹陷的边界大断层,控制着整个凹陷的沉积和构造演化。根据大兴断层的走向特征,将研究区内的大兴断层分为东北段、中段、西南段3段,并对其结合处成因进行了探讨。文中首次将大兴断层断面以三维立体形态展示出来,并对大兴断面的三维几何形态进行了详细的剖析。认为大兴断面是个由多个倾斜面组成的曲面,每个相邻的倾斜面通过轴面而分隔。轴面通过其走向特征,分为横向轴面与垂向轴面,其中横向轴面为平行断层走向的轴面,而垂向轴面则是垂直断层走向的轴面。通过4个横向轴面与2个垂直轴面将大兴断面分为10个区,每个区都有各自的形态与特征。对大兴断层的活动机制进行了探讨,认为大兴断层初期是以多米诺式运动模式为主,后期在翘倾作用下发生旋转,从而形成上陡下缓的犁式断层。其上盘地层的运动模式则是初期与断层同时发生旋转,地层陡且直,在上陡下缓的断面形成后,以斜剪切模式运动,形成滚动背斜。     

白乃庙金矿床控矿构造解析

白乃调金矿区的节理包括东西向剖面共轭剪切节理,北东－北西向平面共轭剪切节理,北北东向剖面共轭剪切节理。与之相应的断层有近东西向逆断层,北东向和北西向的平移断导以及北北东向的斜冲断层。此外,北东向断层的低序次构造亦呈北北东走向,但其性质为平移断层。东西向、北东和北西向断裂形成于南北向挤压构造应力场。它们控制了主要含金石英脉展布。其中,２６号主矿脉就位于北东向平移双断裂－白乃庙断裂的北北东向低序次平移     

Quasistatic propagation of a normal fault: A fracture mechanics model

We have carried out boundary element calculations to simulate quasistatic propagation of a normal fault in the earth's crust under a horizontal tensile loading. Byerlee's frictional law is employed to describe the mechanical behavior of the fault surface. We hypothesize that in order for a normal fault to grow quasistatically, the mixed-mode effective shear stress intensity factor must exceed a threshold value (fracture toughness), a crustal material property. We suggest that the fault grows in a direction of local maximum shear stress. The direction of fault propagation thus depends on the ratio of tensile and shear stress intensity factors. A listric normal fault is likely to form in crustal material with a small shear fracture toughness. A listric normal fault is also more likely to form in crustal material with a high degree of plasticity.The propagation trajectory of an incrementally growing normal fault is examined. As the normal fault extends to a greater depth, the shear stress intensity factor drops, owing to an increase in fault surface friction. The equilibrium depth to which a normal fault will grow is controlled by the far field loading and the fracture mechanical property of the crustal material. The decrease of shear stress intensity with fault length also stabilizes the fault growth.     

海南岛小妹韧性剪切带的纳米尺度

为查明构造性质不明、空间位置不清楚的南海北缘琼南缝合带西段——九所－陵水断裂带,采集断裂带东段小妹韧性剪切带中花岗岩、石榴石石英片岩和花岗质片麻岩3类样品,探讨其纳米尺度特征.扫描电镜(scanning electron microscope,SEM)观测结果表明:这3类岩石存在多种纳米结构和构造,结合野外实践得到的该剪切带纳米颗粒的发育程度与其所受剪切作用有关.纳米颗粒的形成机制可能有:(1) 剪切力作用下层状硅酸盐热分解;(2) 颗粒塑性变形后发生脆性破裂,再经剪切作用研磨而成.与台湾太鲁阁深大断裂带中的韧性剪切带岩石样品进行SEM测试结果对比,发现其纳米颗粒特征和研究区具可比性,据此推测小妹韧性剪切带在区域构造归属上可能与九所－陵水深大断裂带密切相关.      

汊涧斜坡带阜宁期应力场数值模拟及低级序断层发育规律预测

汊涧斜坡带位于金湖凹陷西斜坡南部,第三系沉积期间主要经历了吴堡和三垛运动,形成了复杂的断裂体系,属复杂断块油藏,区内低级序断层较为发育。根据断层平面展布确定阜宁期最小主应力方向为北北西350°,采用有限元法建立地质模型并进行构造应力场数值模拟,计算得出各应力分布,并据此对低级序断层发育规律进行预测。研究表明,汊涧斜坡带阜宁期最大、最小主应力均为水平方向,形成的低级序断层具有张扭性特征;低级序断层的发育主要受最大与最小主应力差值及剪应力控制,主应力差值控制断层优势发育地区,平面剪应力控制断层走向,剖面剪应力控制断层倾向。     

北京云蒙山地区花岗岩穹隆及伸展构造的探讨

北京云蒙山花岗岩为一中生代侵入的花岗岩穹隆,花岗岩穹隆的叶理普遍发育,叶理轨迹基本平行于穹隆的外部边界,并显示出从核部到边部逐渐增强,东南侧明显强于西北侧的特点。变形构造研究显示,花岗岩穹隆的边部及围岩中普遍存在不同层次及不同运动方向的伸展构造。东南侧以具河防口－水峪伸展型韧性剪切带为特征,剪切运动标志显示为从ＮＷ－ＳＥ的正剪切运动,有限应变分析估算其剪切位移量在１０ｋｍ以上,剪切带上部被河防口正     

高邮凹陷真武断裂带西部低级序断层发育规律预测

在应用蚂蚁追踪技术对真武断裂带西部低级序断层进行解释并根据主要断层走向确定阜宁期构造应力方向的基础上,应用构造应力场数值模拟法模拟阜宁期古构造应力的分布,从应力的角度对低级序断层的平面及剖面发育规律进行预测,最后将预测结果与构造解析结果进行对比。研究结果表明,应用蚂蚁追踪技术对低级序断层进行解释获得的蚂蚁属性体断裂痕迹清晰直观,应用效果要优于相干体技术、方差体技术等其他地震属性技术;真武断裂带西部阜宁期最小主应力方向为NW333°-SE153°;低级序断层的发育主要受阜宁期最小主应力及剪应力控制,最小主应力控制断层的优势发育区,平面剪应力控制断层的平面展布,左旋剪应力区主要发育近东西走向断层,右旋剪应力区主要发育北东走向断层,剖面剪应力控制断层的倾向,左旋剪应力区主要发育北倾、西倾断层,右旋剪应力区主要发育南倾、东倾断层。      

Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation

Thrusting fault zone in foreland basins are characterized by highly foliated zones generally enriched in phyllosilicates which can play a major role on the mechanical behaviour of the fault. In this context, investigations of synkinematic clay minerals permit to determine the origin of the fluid from which they precipitated as well as the mechanisms of deformation. Our study is focused on clay mineral assemblages (illite and chlorite) in a major thrust fault located in the Monte Perdido massif (southern Pyrenees), a shallow thrust that affects upper cretaceous-paleocene platform carbonates and lower Eocene marls and turbidites. It implied 3?km of displacement of the Monte Perdido thrust unit with respect to the underlying Gavarnie unit. In this area the cleavage development by pressure-solution is linked to the Monte Perdido and Gavarnie thrust activity. The core zone of the fault, about 6?m thick, consists of an interval of intensely deformed clay-bearing rocks bounded by major shear surfaces. The deformed sediment is markedly darker than the protolith. Calcite-quartz shear veins along the shear planes are abundant. Detailed SEM and TEM observations of highly deformed fault zone samples indicate that clay mineral enrichment in the core zone of the fault is not only related to passive increase by pressure-solution mechanism but that dissolution?Crecrystallization of phyllosilicates occurs during deformation. A mineral segregation is observed in the highly deformed zone. Newly formed 2M ₁ muscovite is present along the cleavage whereas IIb chlorite crystals fill S_V2 shear veins suggesting syntectonic growth of phyllosilicates in the presence of fluids in low-grade metamorphic conditions. These mineralogical reactions act as weakening processes and would favour Monte Perdido fault creeping.     

Analysis of the relationship between displacements and dimensions of faults

Displacement gradients on single fault surfaces are a function of the maximum displacement on a fault and the dimensions of the fault surface. Data on the maximum lateral dimensions (widths) and maximum displacements on normal faults and thrusts, with maximum displacements from 4 mm to 40 km, are used to derive an expression relating width, displacement and material properties. The basis of this expression is a fault growth model in which width is proportional to the square root of displacement. Width/displacement ratios vary systematically with the size of a fault from values of ca 30,000, which are characteristic of a single slip event, to about 10 in the case of thrusts with displacements of 40 km. Rocks from which the fault data are derived have a likely range of shear moduli from ca 0.1 to ca 30 GPa, which is sufficient to account for the range of data.Data on widths and maximum displacements of 308 fault traces recorded on British coalmine plans are shown to be consistent with variation of shear modulus of about half an order of magnitude. Data on 58 further fault traces are shown to be consistent with the fault growth model. Synsedimentary faults may have growth curves characteristically different from those of other faults.It is suggested that the increase in dimensions of a fault is a postseismic process of subcritical crack propagation for which the significant material property is fracture toughness.     

Relay zone geometry and displacement transfer between normal faults recorded in coal-mine plans

Overlap lengths, separations and throw gradients were measured on 132 relay zones recorded on coal-mine plans. Throws on the relay-bounding fault traces are usually ≤ 2 m and individual structures are recorded on only one seam. Throw gradients associated with relay zones are not always higher than on single faults, but asymmetry of throw profiles is diagnostic of relay zones. Bed geometries around larger faults in opencast mines are used to assess the displacement accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault-parallel plane. Three-dimensional structure is defined for two relay zones, each recorded on five seam plans. These relay zones are effectively holes through the fault surfaces and overlap occurs between salients or lobes of the parent fault surfaces. Lobes initially terminated at tip-lines but, as the faults grew, gradually rejoined the main fault surfaces along branch lines. This type of relay zone originates by bifurcation of a single fault surface at a locally retarded tip-line and is an almost inevitable result of a tip-line irregularity.     

构造物理模拟和PIV有限应变分析对构造裂缝预测的启示

油气储层中构造裂缝发育与有限应变状态关系密切,为了探索有限应变分析与构造裂缝预测的新技术方法,此次研究设计完成了一组单侧挤压收敛模型的物理模拟实验,并引入粒子图像测速(PIV,Particle Image Velocimetry)技术对实验过程进行了定量化分析。实验模型在垂向上为含粘性层的多层结构,实验结果形成了一个肉眼可见的箱状褶皱。通过PIV技术可以获取实验模型变形演化过程中各阶段的位移场数据,计算出各阶段的增量应变,实现从初始状态到褶皱形成之后整个变形过程的有限应变分析,探讨构造裂缝成因机制和分布规律,进行定量化裂缝预测。挤压变形过程初期,应变分布范围很广,有限应变较弱(约4%~8%),在挤压方向上的线应变表现为弱压应变,在垂向上的线应变表现为弱张应变,这种现象是褶皱和断层产生前平行层缩短和层增厚的纯剪变形结果,也是区域型张裂缝和剪裂缝形成的主要机制。褶皱和断层即将发育之时至发育之后,应变局限在断层发育的剪切带及附近区域,有限应变表现为较强(达20%)的剪切应变和剪切张应变,是断层面附近简单剪切变形作用的结果,也是局部型剪裂缝和张剪裂缝形成的主要机制。     

Mylonitization in the lower plate of the Buckskin-Rawhide detachment fault,west-central Arizona: Implications for the geometric evolution of metamorphic core complexes

In metamorphic core complexes it is commonly unclear whether lower plate mylonites formed as the down-dip continuation of a detachment fault, or whether they represent a subhorizontal shear zone that was captured by a more steeply dipping detachment fault. Detailed microstructural, fabric, and strain data from mylonites in the Buckskin-Rawhide metamorphic core complex, west-central Arizona, constrain the structural development of the lower plate shear zone. Widespread exposures of ∼22–21 Ma granitoids of the Swansea Plutonic Suite enable us to separate Miocene strain coeval with core complex extension from older deformation. Mylonites across the lower plate consistently record top-to-the-NE-directed shear. Miocene quartz and feldspar deformation/recrystallization mechanisms indicate ∼450–500 °C mylonitization temperatures that were relatively uniform across a distance of ∼35 km in the extension direction. Quartz dynamically recrystallized grain sizes do not systematically vary in the extension direction. Strain recorded in the Swansea Plutonic Suite is also relatively uniform in the extension direction, which is incompatible with models in which lower plate mylonites form as the ductile root of a major detachment fault. Altogether these data suggest the mylonitic shear zone initiated with a ≤4° dip and was unroofed by a more steeply dipping detachment fault system. Lower plate mylonites in the Buckskin-Rawhide metamorphic core complex thus represent a captured subhorizontal shear zone rather than the down-dip continuation of a detachment fault.     

郯庐剪切带的性质和意义

沿郯庐断裂带从大别山东麓经山东中部至辽北吉南的新宾—桦甸地区,暴露的早前寒武纪结晶岩石中存在着一系列北北东走向的大型韧性剪切带,其最大宽度达20km,走向断续延伸近2000km,它们分别在大别、鲁西和新宾地区形成了巨大的弧形牵引构造。剪切带中不同尺度组构要素的几何学,指示其中曾经发生了一致的大幅度左行位移;变形岩石的显微构造和矿物组合特征,说明这一韧性剪切带早期形成于低角闪岩相条件下,并且在抬升和冷却过程中经历了绿片岩相条件下的递进变形。山东中部晚元古代以后的沉积不整合于韧性剪切带及其变形岩石之上,中生代未期脆性的郯庐断裂系统追踪并改造了基底岩石中的韧性剪切带。     

广东莲花山断裂带韧性剪切带变形特征及其与成矿的关系

莲花山断裂带是中国东南陆缘重要的NE向构造带。该断裂带不仅是区域上重要的二级构造单元分界线,也控制着广东省最重要的锡铜多金属成矿带。前人研究表明,莲花山断裂带内的韧性变形与锡铜多金属成矿关系密切,但对于莲花山断裂带内的韧性变形展布特征及其对成矿作用的贡献,还存在着较多争议。本次研究,通过对莲花山断裂带进行大比例尺的矿田构造填图,实测典型地质剖面等手段,结合拉伸线理产状的测量和显微构造的观察,认为断裂带内的韧性变形由自北向南一系列近NE60°走向的剪切带雁列展布而成,各剪切带之间呈大致平行展布。在韧性变形之后,这些雁列状的剪切带又被30°走向的脆性断层所切割。莲花山断裂带内的韧性变形控制着矿体的形态和规模,后期岩浆-热液活动利用先存韧性剪切带的空间,成矿元素在韧性变形的裂隙中沉淀富集成矿。莲花山断裂带内找矿勘探工作部署应该围绕断裂带内韧性变形的区域,并注意韧性变形附近次一级的容矿裂隙。     

Evolution of the Large-scale Active Manisa Fault,Southwest Turkey: Implications on Fault Development and Regional Tectonics

This paper aims to illustrate and discuss mechanism(s) responsible for the growth and evolution of large-scale corrugated normal faults in southwest Turkey. We report spectacular exposures of normal fault surfaces as parts of the Manisa Fault - a ?50-km-long northeast-ward arched active fault that defines the northwestern edge of the Manisa graben, which is subsidiary to the Gediz Graben. The fault is a single through-going corrugated fault system with distinct along-strike bends. It follows NW direction for 15 km in the south, then bends into an approximately E-W direction in the northwest. The fault trace occurs at the base of topographic scarps and separates the Quaternary limestone scree and alluvium from the highly strained, massive bed-rock carbonates. The fault is exposed on continuous pristine slip surfaces, up to 60 m high. The observed surfaces are polished and ornamented by well-preserved various brittle structural features, such as slip-parallel striations, gutters and tool tracks, and numerous closely spaced extension fractures with straight or crescentic traces. The rocks both in the footwall and hanging-wall of the fault possess a well-developed fault rock stratigraphy made up, from structurally lowest to the top, of massive undeformed recrystallized limestone, a zone of cemented breccia sheets, corrugated polished slip planes, and first brecciated, then unbrecciated scree.

The observed slip surfaces of the Manisa Fault contain two sets of striations that suggest an early phase of sinistral strike-slip and a subsequent normal-slip movements. The first phase is attributed to: (i) approximately E-W-directed compression that commenced during either (?) Early-Middle Pliocene time or (ii) the current extensional tectonics and consequent modern graben formation in southwest Turkey that initiated during the Plio-Quaternary. During this period, the Manisa Fault was reactivated and it became a major segment. Stress inversion of fault slip data suggests that southwest Turkey has been experiencing multidirectional crustal extension, with components of approximately N-S, E-W, NE-SW and NW-SE extension. Following the reactivation, the inherited fault segments were connected to each other through interaction, linkage and amalgamation of previously discontinuous and overlapping smaller stepping adjacent faults. Linkage was via the formation of new connecting (breaching) fault(s) or by curved propagation of fault-tips. The result is a single through-going corrugated fault trace with distinct along-strike bends. The final geometry of the Manisa Fault is thus the combined result of reactivation and continuing interaction between previously discontinuous segmented fault traces.