Chapter 4 Geological Structure 第四章 地质构造 - PowerPoint PPT Presentation

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Chapter 4 Geological Structure 第四章 地质构造
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Chapter 4 Geological Structure 第四章 地质构造

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  1. Chapter 4 GeologicalStructure第四章 地质构造

  2. §4-1 geological time and Chronological scale地质年代与地质年代表 一、Geological Time Geological time is a method of ordering and measuring past events. The ordering of events uses a group of observational methods known as: 1 Absolute dating methods(绝对年代法) 2 Relative dating methods(相对年代法)

  3. 1 Absolute dating methods Absolute dating methods are those that generate an age in years. There are two principal methods: one is the method which rely on event in the geological record with very strong annual cyclicity(周期性), such as tree growth rings ,coral growth cycles varves(纹层)(annual clay sediment layers). Another Methods is more commonly used now days which rely on the decay of naturally occurring radiogenic isotopes:

  4. Radiometric dating is not without difficulties but is by far the most widespread method applied to determine absolute ages between 100 and 4500 My. Uranium(铀), Thorium(钍)and Potassium (钾)are by far the most common radiogenic isotopes in the Earth's crust. Radiocarbon is important in dating organic remains from the relatively recent past.

  5. 2 relative dating methods Relative dating methods use geological principles to place events in chronological order.which include: ♣ strata superposition method(地层层序法) ♣ fossil succession method(化石演变法) ♣ the method of rock layers contact relation (岩层接触关系法).

  6. The youngest layer The oldest layer ♣The principle of superposition states that older beds are covered by younger beds. In other word, the youngest unit is usually at the top in a sedimentary sequence.

  7. ♣The principle of fossil succession states that organisms evolve through time so that particular forms can be used as age markers wherever they are found.

  8. ♣ The method of rock layers contact relation states that the contact relations among rock layers is the history records of crust movement, magma activities. So geological events can be ordered by the relation of rock layers , these includes :

  9. ① the relations among sedimentary rock , (沉积岩之间的接触关系) ② the relations among the igneous rock, (岩浆岩之间的接触关系) ③ the relation between sedimentary rock and igneous rock. (沉积岩和岩浆岩之间的接触关系)

  10. ①The relations among sedimentary rock The relations among sedimentary rock can be divided into: conformity (整合) Unconformity(不整合). The conformity means that strata was formed in a stable sedimentary environment, the dip and strike of strata are basically the same.

  11. conformity (整合接触关系)

  12. Unconformity(不整合). The unconformity mean there is a break in sedimentation, a period of erosion or an episode of deformation, Unconformities range from minor erosional breaks to strong angular discordances in bedding. An unconformity indicates a period where no rock record is accumulated. They are time-breaks of indeterminate length.

  13. 角度不整 合 接 触 整合接触 平行不整 合 接 触

  14. ②the relations among the igneous rock, 岩浆岩之间的接触关系 Cross-cutting relationships among igneous rocks indicate that intrusion rocks must be younger than the rocks they cut.

  15. ③ the relation between sedimentary rock and igneous rock. Cross-cutting relationships between igneous rocks and sedimentary rock Indicate that sedimentary rock included pebbles and fragments must be older than the host rock containing them.

  16. 二、Chronological scale The geologic time scale was originally a set of relative dates but the various eons(宙), eras(代), periods(纪)and epochs(世)have now been accurately dated with the aid of radiometric methods. The important dates are: 4,600 My - the age of the Earth and Solar System 3,600 My - the earliest life 570 My - the first appearance of abundant and varied organic forms 200 My - the break-up of the super continent 66 My - the disappearance of the dinosaurs

  17. 么 富 有 想 象 力 的 比 喻 !

  18. §4-2 Basic shape and classification of geological structure 地质构造的基本形态和分类 一、intruduction 二、spacial state of strata(地层的产状要素) 三、水平构造和单斜构造 (Horizontal and inclined structure ) 四、Folding(褶皱构造) 五、Fracturing structure断裂构造 六、地质构造在地质图中的表现形式

  19. 一、intruduction Geological structure is the study of the permanent deformation and rock failure created by the changes in stress through geologic time. It is by far the most important aspect of geology for the engineer to understand. Tectonic构造processes are responsible for the many discontinuity planes (不连续面)(fractures裂隙, faults断层, joints节理) that permeate rock masses controlling their strength, stress-strain characteristics and the transmission and storage of fluids.

  20. Structures may be conveniently subdivided into two groups: brittle structures 脆性构造 recording the brittle-elastic failure弹脆性破坏 of rocks in the past. Faults and joints fall in this broad category. ductile structures 柔性构造 preserving the permanent viscoplastic(粘塑性) deformation of rock throughout geologic time. Folds and metamorphic foliations are the expression of this type of structure.

  21. The most striking features of rocks as engineering materials is that they are not simple, isotropic各向同性的, elastic and continuous but very complex, strongly anisotropic(各向异性的), anelastic(粘弹性) discontinuous. It is virtually impossible to deduce the stress history of rocks from their observed deformation. There are always many ambiguou不明确的deformation paths路径that could have been followed to produce what is observed.

  22. The study of structure involves the careful recording of the orientation of lines and planes in rock masses in order to deduce the three-dimensional geometry of the distorted变形的 crust.

  23. 二、spacial state of strata(地层的产状要素) Planes can be defined in space by their inclination or dip and their strike, the bearing of the line of intersection of the plane and a horizontal surface. Notice that the bearing of the projection of the dip on a horizontal surface is in a direction at right angles to the strike. This is called the dip direction.

  24. Dip :倾角 Dip direction: 倾向 Strike:走向

  25. 三、水平构造和单斜构造 (Horizontal and inclined structure ) Inclined structure Horizontal structure

  26. 四、Folding • The definition of folding (断层的定义) • Folds result from the plastic deformation of rocks at low strain-rates, usually under elevated temperature and pressure conditions. • 2 The shape description (形态描述) • Folds are broadly subdivided into anticlines背斜(upwards convex凸的) and synclines向斜(downwards convex

  27. 向斜 背斜

  28. 轴面 Pivot 枢纽 翼部 翼部 向斜 背斜 In synclines and anticlines, the axial plane is the plane of symmetry passing through the apex (顶点)of the fold. The line of intersection of the fold apex and the horizontal plane is called the axis of the fold.

  29. 3 the classification of folding (1) According to the Orientation of axial plane The orientation of the axial plane relative to the horizontal together with the orientation of fold limbs翼部allow subdivision into upright (axial plane vertical, limbs symmetric), overturned (axial plane moderately inclined, one limb overturned), or recumbent平卧的(axial plane near horizontal, one limb inverted).

  30. Recumbent 平卧的 Inclined 倾斜的 Overturned 倒转的 Upright 直立的

  31. (2)according to pivot location state Inclined fold Horizontal fold

  32. (3)According to the tightness of folding The tighness of folds can be described as open (limbs dip gently), tight (limbs dip steeply) or isoclinal (limbs are parallel).

  33. Fault 断层 Jointing节理 Fracturing structure (Fragile rock 脆性岩石) Fracture plane 五、Fracturing structure断裂构造

  34. 1 Jointing节理 (1)The definition of Jointing Joints are discontinuities on which there has been little or no displacement in shear (in contrast to faults). Joints are ubiquitous (普遍存在的)in igneous, metamorphic and sedimentary rocks. They are evidence of brittle failure of the rock mass at some stage in the deformation history.

  35. (2)The formation of joints(节理的形成) ◆ joints in igneous rock(岩浆岩中的节理) Joints in igneous rocks are often associated with the tensile stresses generated by shrinkage as the rock cools. The joints form normal (at right angles) to the cooling surface. The margins of lava flows, sills(岩床), dykes (岩墙)and plutons(侵入体)commonly form the cooling surfaces.

  36. 岩浆岩中的节理构造

  37. ◆ Joints caused by crust movement (构造节理) a: Joints in Compressive Stress Fields(压应力节理) In compression, joints develop in the conjugate共轭的shear directions (the orientation of symmetric fracture planes) making the lower angle with the major principal stress direction. Shear joints are often groooved, striated有条纹的, polished or slickensided(有光面的)by even small amounts of shear displacement.

  38. b: Joints in Tensile Stress Fields(张应力场下形成的节理) In tension, joints develop by stretching normal to the tensile stress direction which is usually the minor principal stress. Tension joints are rough (unless subsequently weathered). In coarse grained rocks such surfaces may be very rough.

  39. C Joints in Folding(褶皱构造中的节理) Several sets of joints may develop in response to folding. Conjugate shear joints oblique倾斜的to the fold axis are develpoed by compression. Tension joints can develop due to bending, particularly in the vicinity of the fold hinge(枢纽). Joints parallel to the strike of the fold axis are called strike joints; those parallel to the limb dip are known as dip joints. Such joints are generally tensile fractures.

  40. (3) the features of joints(节理的特征) Joints have many important properties as planes of weakness in rock masses: ▼ Orientation 产状 - strike and dip or dip and dip-direction. ▼ Spacing间距 - the frequency or number of discontinuities per unit length.

  41. ▼ Aperture(口径,) - the mean distance between wall rock surfaces. ▼ Persistence(连续性) - the continuity of joints or trace length. ▼ Surface Roughness粗糙度 - the property controlling friction between surfaces. ▼ Infill充填 - the presence or absence of breccia角砾, or surface coatings of minerals.

  42. (4)The engineering meaning and evaluation of joints (节理的评价方法和节理研究的工程意义) Joints and other discontinuities such as faults, cleavage(解理,劈理), metamorphic foliation(叶理,面理), and bedding planes control many important properties of rock masses including: Strength, Compressibility, Permeability. evaluation methods step 1 to choose the representative place step 2. Measuring, and making statistics table of joints step 3. making the joint rose flower map

  43. N 0 10 20 90 W E joint rose flower map

  44. 2 Faulting 断层 (1)the definition of faulting Faults are planar discontinuity surfaces along which there has been significant displacement in shear. In common with all planar structures, a fault has a strike and dip.