GL4 rock deformation

advertisement

GEOLOGY STUDY GUIDE

Module exam GL4 June 2005

R O C K D E F O R M A T I O N

Geology Department, Greenhead College, Huddersfield.

Syncline at Jeffrey’s Mount, Tebay

Your name …………………………………………………………… Date ………………………….

LEARNING TARGETS

Margin notes

When you have completed this study guide, you will:

Have understood the terms geologists use to describe rock deformation

Have experimented on brittle and ductile materials to see how they deform

Studied the stress fields which produce the three main fault types

Described the evidence of faulting which can be seen in the field

Extended your knowledge of fold types

Learnt examples of folding types

______________________________________________________________________________________________________________________________

VC/Dept/Geol/022

page 1

GEOLOGY STUDY GUIDE

Module exam GL4 June 2005

Resources

Here is a choice of resources to use. You do not need to look at them all but clearly the more you read the better your knowledge of case studies will be. Tick the box once you have used the resource.

If you read a photocopied extract then highlight it to help you reread it for revision. If you make notes from a video tape make sure that the notes are headed with the name of the tape so that you know the source of your information. Case studies are very useful for essay questions so you should keep a separate list of the examples that you have researched.

SG1

SG2

SG3

SG4

SG5

SG6

SG7

SG8

SG9

SG10

SG11

SG12

SG13

SG14

Understanding Geology

David Webster p 93-96

Geoscience

Edwards and King p 136-144

Geological Science

by Andrew McLeish p 147-160

Exercise on factors which affect rock deformation

Angelina unstretched

. Geol. Today Nov-Dec 1992

Faulting exercise

Plunging folds exercise

Exercise on faulted folds

SWAN Rule examples

CD Rom

Visualising Geology in 3D

Folding and Faulting

Library Skinner, B.J. and Porter, S.C.,

The Dynamic Earth

Chap 14

Diagrams of folds from SG3 p156

Diagram to show axial plane cleavage

Video

Structural Geology

Tapes 56 and 60

21 mins

Websites

www.geolsoc.org.uk/ Go to Teaching Resources http://www.geolsoc.org.uk/template.cfm?name=thrust_belts http://www.geologyshop.co.uk/struct~1.htm

http://homepages.nasuwt.net/sevans/Photos_of_Formations.htm#Top%20of%20Page http://cwx.prenhall.com/bookbind/pubbooks/hamblin2/chapter7/deluxe.html

There are many other websites you could search.

______________________________________________________________________________________________________________________________

VC/Dept/Geol/022

page 2

GEOLOGY STUDY GUIDE

Module exam GL4 June 2005

Margin notes

ACTIVITY 1 : ROCK DEFORMATION

TASK 1

DEFINITIONS

Define and explain, using diagrams from SG2 p137-138:

Ductile

Brittle

Deformation

Tension

Elastic deformation

Compression

Fracture/Rupture

Stress Strain Shear Elastic limit

TASK 2

PRACTICAL

Using materials such as plasticene, blackboard chalk and sponge, test how they deform under stress of different types.

Make out a table showing how each material deforms under

tension

and

compression

.

TASK 3

BRITTLE AND DUCTILE DEFORMATION

As stress increases rocks deform in different ways. Laboratory tests give results which can be graphed.

Draw Fig 8.4 from SG2 p138. Describe and explain how this particular rock deformed under stress when tested.

TASK 4

FACTORS CONTROLLING DEFORMATION WITHIN THE EARTH

Summarise how materials deform by completing the blank spaces in SG4.

TASK 5

STRAIN ELLIPSOIDS

Using plasticene or blue tack form a cube. Trace a circle on one of the faces with a pencil. Now deform it under tension, compression and shear forces. For each force, record the change in shape you observe.

Strain ellipsoids

are indicators which geologists use to find out about stress fields in the crust.

List the natural strain ellipsoids that might be useful for analysis by geologists.

TASK 6

Read SG5

Angelina unstretched

. Geol. Today Nov-Dec 1992 and answer the questions that follow.

Deadline for

Angelina unstretched

answers……………………………………….

Use this box for notes

______________________________________________________________________________________________________________________________

VC/Dept/Geol/022

page 3

GEOLOGY STUDY GUIDE

Module exam GL4 June 2005

Margin notes

ACTIVITY 2 : FAULTING

TASK 7

FAULT TYPES

Use SG6 to remind yourself how tension, compression and shear forces produce faulting in brittle rocks.

TASK 8

STRESS COMPONENTS

The forces acting on a rock can be resolved into three principal stresses acting at right angles to one another. The stress field consists of P max

, P min and P inter

and they are shown with arrows as shown in SG2 p139.

Analyse

normal, reversed

and

strike-slip faults

in terms of stress components in the stress field by drawing diagrams using stress arrows.

TASK 9

FAULT EVIDENCE

Find a variety of types of evidence which show that faulting has taken place in a rock sequence. Use your own field notes, hand specimens, slides and photos from textbooks.

You should be able to find 6/7 forms of evidence that faulting has occurred.

TASK 10

REACTIVATED FAULTS

Read, highlight and learn this information:

A fault plane is a line of weakness in the crust at a very specific point. Subsequent stresses within the crust may be released by fracturing of rocks in the same place.

Movements along a fault can be in the same direction as initial movement, if the stress field continues in the same direction, but if the stress field changes then movements can be in the opposite direction.

It is possible for major faults to continue to be active for hundreds of millions of years, in which case the total movement on them can be many hundreds of kilometres. However on faults with repeated movements it is difficult to assess the total displacement because movement could be vertical and/or lateral in both directions.

Slickensides

are a useful indicator of direction of movement on faults but they will record only the final movement. Previous slickensides will be removed by later scratches along the fault plane due to friction.

TASK 11

FOLLY DOLLY FALLS

A local example of a fault showing many interesting features can be seen in

Meltham. Bring field note books and wear wellies. You have to stand in the river to study the fault.

Date of field trip…………………………………………………………

Meeting place……………………………………………………………

Meeting time…………………………………………………….………

Use this box for notes

______________________________________________________________________________________________________________________________

VC/Dept/Geol/022

page 4

GEOLOGY STUDY GUIDE

Module exam GL4 June 2005

ACTIVITY 3 : FOLDING

Margin notes

TASK 12

REVISE WHAT YOU KNOW ALREADY

Revise

synforms, antiforms, synclines

and

anticlines

by writing out definitions of each. Use coloured diagrams to show which rocks are youngest and which are oldest within the folds.

TASK 13

FOLD TYPES

Draw diagrams to show these features, using SG 3 p.156 or SG12 interlimb angle axial plane fold axis open fold hinge tight fold

limb

upright attitude inclined attitude amplitude overturned fold wavelength recumbent fold cylindrical fold

TASK 14

PLUNGING FOLDS

Complete SG 7 to help understand the three-dimensional appearance of plunging folds.

Remember the ASSO rule: anticlines plunge in the same direction as the V shape synclines plunge in the opposite direction.

TASK 15

AXIAL PLANE CLEAVAGE

Use SG13 to show the relationship between axial plane cleavage and bedding planes. Describe the stress field which produces axial plane cleavage. Use specimens and photos to help understand the relationship between the two.

TASK 16

FAULTED FOLDS

Look at SG8 and complete the block diagrams to show that you understand how folds and faults occur as outcrop patterns on maps.

TASK 17

CASE STUDIES OF FOLDS

Use a variety of resources to analyse folds and their terminology. Look at slides, photos in textbooks and SG9.

TASK 18

SUMMARY NOTES

You need to learn this topic now.

Summary notes deadline .........................................

Use this box for notes

______________________________________________________________________________________________________________________________

VC/Dept/Geol/022

page 5

Download