Chapter 4 Geological Structure

第四章 地质构造

§4-1 geological time and Chronological scale地质年代与地质年代表

一、一、 Geological TimeGeological Time Geological time is a method of ordering and meaGeological time is a method of ordering and mea

suring past events. The ordering of events uses a gsuring past events. The ordering of events uses a group of observational methods known as: roup of observational methods known as:

1 1 Absolute dating methods( Absolute dating methods( 绝对年代法绝对年代法 ))

2 2 Relative dating methodsRelative dating methods （相对年代法）（相对年代法）

1 1 Absolute dating methodsAbsolute dating methods

Absolute dating methods are those that generate a

n age in years. There are two principal methods: one

is the method which rely on event in the geological r

ecord with very strong annual cyclicity( 周期性 ), suc

h as tree growth rings ,coral growth cycles varves

（纹层） (annual clay sediment layers). Another Met

hods is more commonly used now days which rely o

n the decay of naturally occurring radiogenic isotope

s:

Radiometric dating is not without difficulties but i

s by far the most widespread method applied to det

ermine absolute ages between 100 and 4500 My.

Uranium( 铀 ), Thorium （钍） and Potassium

（钾） are by far the most common radiogenic isoto

pes in the Earth's crust. Radiocarbon is important in

dating organic remains from the relatively recent pa

st.

2 2 relative dating methodsrelative dating methods

Relative dating methods use geological principle

s to place events in chronological order.which incl

ude:

♣ 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） .

♣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.

The youngest layer

The oldest layer

♣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.

♣ 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 ：

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）

① The 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.

conformity （整合接触关系）

Unconformity （不整合） .

The unconformity mean there is a break in sedi

mentation, a period of erosion or an episode of de

formation, Unconformities range from minor erosi

onal breaks to strong angular discordances in be

dding. An unconformity indicates a period where

no rock record is accumulated. They are time-bre

aks of indeterminate length.

整合接触 平行不整合 接 触

角度不整合 接 触

② the 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.

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.

二、二、 Chronological scaleChronological scale

The geologic time scale was originally a set of relative date

s but the various eons （宙） , eras （代） , periods （纪） a

nd epochs （世） have now been accurately dated with the ai

d 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

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§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

Geological structure is the study of the permanent deformatio

n and rock failure created by the changes in stress through geo

logic time. It is by far the most important aspect of geology for t

he engineer to understand. Tectonic 构造 processes are respo

nsible for the many discontinuity planes （不连续面） (fracture

s 裂隙 , faults 断层 , joints 节理 ) that permeate rock masses co

ntrolling their strength, stress-strain characteristics and the tran

smission and storage of fluids.

一、 intruduction

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.

The most striking features of rocks as engineerin

g materials is that they are not simple, isotropic 各向同性的 , elastic and continuous but very complex, str

ongly anisotropic( 各向异性的 ), anelastic( 粘弹性 ) dis

continuous. It is virtually impossible to deduce the st

ress history of rocks from their observed deformatio

n. There are always many ambiguou 不明确的 deform

ation paths 路径 that could have been followed to pr

oduce what is observed.

The study of structure involves the careful recording of the

orientation of lines and planes in rock masses in order to dedu

ce the three-dimensional geometry of the distorted 变形的 cr

ust.

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.

Dip ：倾角Dip direction ： 倾向Strike ：走向

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

Horizontal structure Inclined structure

四、 Folding

1 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

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.

轴面

Pivot 枢纽

翼部翼部

向斜 背斜

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 subdivi

sion into upright (axial plane vertical, limbs symmetric), ove

rturned (axial plane moderately inclined, one limb overturne

d), or recumbent 平卧的 (axial plane near horizontal, one li

mb inverted).

Upright直立的

Inclined倾斜的

Overturned倒转的

Recumbent平卧的

（ 2 ） according to pivot location state

Horizontal foldInclined fold

（ 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).

五、 Fracturing structure 断裂构造

Fault 断层

Jointing 节理

Fracturing structure（ Fragile rock 脆性岩石）

joints obviousnot

fault Obviousnt displaceme Relative

Fracture plane

1 Jointing 节理

（ 1 ） The definition of Jointing

Joints are discontinuities on which there has been lit

tle or no displacement in shear (in contrast to faults). Joi

nts are ubiquitous ( 普遍存在的 )in igneous, metamorphi

c and sedimentary rocks. They are evidence of brittle fai

lure of the rock mass at some stage in the deformation

history.

（ 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 t

he tensile stresses generated by shrinkage as the r

ock cools. The joints form normal (at right angles) t

o the cooling surface. The margins of lava flows, sill

s （岩床） , dykes （岩墙） and plutons （侵入体） commonly form the cooling surfaces.

岩浆岩中的节理构造

◆ 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 di

rections (the orientation of symmetric fracture planes) making the l

ower angle with the major principal stress direction. Shear joints ar

e often groooved, striated 有条纹的 , polished or slickensided （有

光面的） by even small amounts of shear displacement.

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 stre

ss direction which is usually the minor principal stress. Tension joint

s are rough (unless subsequently weathered). In coarse grained roc

ks such surfaces may be very rough.

C Joints in Folding （褶皱构造中的节理）

Several sets of joints may develop in response to folding. Co

njugate shear joints oblique 倾斜的 to the fold axis are develpo

ed by compression. Tension joints can develop due to bending,

particularly in the vicinity of the fold hinge （枢纽） . Joints parall

el to the strike of the fold axis are called strike joints; those para

llel to the limb dip are known as dip joints. Such joints are gener

ally tensile fractures.

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.

（ 3 ） the features of joints （节理的特征）

▼ 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.

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 jointsstep 3. making the joint rose flower map

（ 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）

joint rose flower map

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（ 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.

2 Faulting 断层

（ 2 ） the description of shape 断层的形态要素

断层倾角

下盘

断层走向

断层面

上盘

相对移动方向

◐ According to the direction of relative movement of the two blocks,Faults are divided into:

（ 3 ） Fault Types

Normal Faul 正断层Reverse Fault 逆断层 Strike-slip Fault 平推断层

Normal FaultIn normal faulting, the hanging wall block moves down relative to the footwall block. The fault plane usually makes a high angle with the surface (> 45 degrees). Normal faults are associated with tension.

Normal Fault

Reverse Fault

In reverse faulting, the hanging wall block moves up rela

tive to the footwall block. The fault plane usually makes a

low angle with the surface (< 45 degrees). Reverse faults

are associated with crustal compression and are also kn

own as thrust faults.

Reverse Fault

Strike-slip Fault

In strike-slip faulting, the two blocks move either to the lef

t (sinistral ) or to the right (dextral) relative to one anothe

r. Strike-slip faults are associated with crustal shear and a

re also known as wrench faults( 扭性 ).

Strike-slip Fault

◐ According to the stress condition of fault happening

Faults of different types are charcteristic of the stress fi

eld in which they formed. Faults are nothing more than f

ailure of the crust in shear. The crust is generally in a tri

axial state of stress with three principal stress directio

ns, one vertical and two horizontal.

In normal faulting, the largest

(most compressive) stress is

vertical. The smallest and

intermediate stresses are

horizontal.

Tension faulting

In reverse faulting, the smallest

(least compressive) stress is

vertical. The largest and

intermediate stresses are

horizontal.

Compressive faulting

In strike-slip faulting, the intermediate stress（中间主应力） is vertical. The largest and smallest stresses are horizontal.

Shear faulting

断层组合分类倾向不同的正断层形成地堑

倾向相同的正断层形成地垒

倾向相同的逆断层形成叠瓦

状构造

六、地质图以及地质构造在地质图中的表现形式

◈ 地质图的基本概念 ◈ 地质图的规格 （图名、比例尺、图例、各种符号） ◈ 地质图的分类 地形地质图 水文地质图 工程地质图 隧道工程地质图 ; 桥梁工程地质图 建筑工程地质图… ..

1 地质图的基本知识

2 地质构造在地质图中的表现形式

(1) 水平岩层在地质图中的表现形式

(2) 倾斜岩层在地质图中的表现形式

(3) 褶皱构造地质图中的表现形式

(4) 断裂构造在地质图中的表现形式

褶皱构造地质图中的表现形式

断层切割褶皱后在地质图中的表现规律

断层切割倾斜岩层造地层在地质图中突然中断

This image shows San Andreas Lake and Crystal Springs reservoir from the air, looking South East from here ， The highway paralleling the lakes to the left is

Interstate 280 the most beautiful urban highway in the United States''. (And it is indeed very scenic.)

A small normal fault.

桥梁工程地质图

地层综合柱状图

地质构造与道路工程

A 台易产生

顺层滑动

B 台位于断层带上

C 台较为有利