GEOLOGY STUDY GUIDE Module exam GL1 June 2004

METAMORPHISM
Geology Department, Greenhead College, Huddersfield.

Thin section of garnet mica schist x 10 magnification

Your name .....……………………...... Date ...... ……………......
LEARNING TARGETS
margin notes
When you have completed this study guide, you will:
●  Be able to define metamorphism
●  Recognise the main metamorphic rocks
●  Know the difference between contact and regional metamorphism
●  Recognise and understand metamorphic minerals
●  Be able to draw diagrams to show metamorphic textures in microscope thin section
●  Have tested your knowledge in a variety of ways.
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.



 / MET1
MET2
MET3
MET4 / Understanding Geology David Webster p 80-85
Geoscience Edwards and King p 124-134
Geological Science by Andrew McLeish p 139-145
Specification notes
Websites



 / www.geolsoc.org.uk/ Go to Teaching Resources
www.science.ubc.ca/~geol202
www.geologyshop.co.uk/metamo~l.htm
www.brookes.ac.uk/geology/8361/1998/freya/met.html
There are other websites you could search.
Margin notes
ACTIVITY 1
TASK 1 DEFINITION
Read MET 1 p 80 and MET 4.
1.  What is given as a definition of metamorphism?
2.  Where in the crust will rocks be under greatest pressure?
3.  What happens to the minerals in rocks when they are subjected to heat and/or pressure?
4.  If clay is heated in the sun to make a brick is it being metamorphosed?
5.  If clay is heated in a kiln to 1400oC to make a brick is it being metamorphosed?
6.  What happens to the texture of rocks when they are subjected to heat and/or pressure?
The specification uses the definition below. Write it out on plain paper and define all the words and phrases. Decorate to taste to help you remember the definition.
Metamorphism is the solid-state recrystallisation of pre-existing rocks in response to changes in temperature and/or pressure. There can be changes in texture and mineralogy of metamorphic rocks.
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TASK 2 SOLID STATE RECRYSTALLISATION
The term we use for the process of metamorphism is solid state recrystallization. “Recrystallization of the minerals in the original rock does occur but it is not total recrystallization. Some of the crystals may melt, particularly where they are in contact with other crystals under pressure. Most crystals remain in a solid state but take up a different shape. Elements and ions are able to be mobilised as the rock is heated and may be able to move into new crystal lattices which will produce minerals of different compositions. What is important is that new minerals may develop without the addition of new chemical elements.”
Draw diagrams to show what you understand by this paragraph.

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Margin notes /

ACTIVITY 2 : CONTACT METAMORPHISM

TASK 3 METAMORPHIC AUREOLES AND BAKED MARGINS
Read MET 1 p 81 and MET 4 on contact metamorphism. Answer these questions:
●  Define a metamorphic aureole.
●  Explain how it can form.
●  Draw a diagram of your own to show the effect of heat only on surrounding country rocks. How can you show in your diagram that the effect of heat is greatest on rocks close to the pluton?
●  Small igneous intrusions such as dykes and sills are not hot enough to have a large-scale effect on country rocks. Draw a diagram of your own to show how baked margins are formed.
TASK 4 EFFECTS ON SANDSTONE AND LIMESTONE COUNTRY ROCKS

How does the heat from the pluton change limestone and sandstone?

Draw diagrams to show the textural changes as these rocks are metamorphosed to marble and metaquartzite.
TASK 5 PELITIC ROCKS – SHALES - MUDROCKS
Pelitic is a term used in metamorphic geology for any rocks originally made from clay particles. New minerals are likely to develop if pelitic rocks are metamorphosed because the chemistry of clays is complex and they are chemically reactive.
In class we will explain the formation of spotted rocks and hornfels and their characteristic minerals, chiastolite, and cordierite.
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ACTIVITY 3 : REGIONAL METAMORPHISM
TASK 6 WHERE DOES REGIONAL METAMORPHISM TAKE PLACE?
Read MET 4 and other resources. Make a brief note to remind yourself about which parts of the earth’s crust are likely to be under particularly high pressures and so cause crustal rocks to change even though temperatures are not hot enough for the rocks to melt.
TASK 7 METAMORPHIC TEXTURES
Use MET 4 as reference for this section. We can see that pressure and tension have an effect on the alignment of minerals during regional metamorphism. The texture that results is called foliation. There are three main types of foliation. In class we will draw diagrams to illustrate all three – slaty cleavage, schistosity and gneissose banding - and relate them to their characteristic rock lithology.
Margin notes / TASK 8 INDEX MINERALS IN PELITIC ROCKS
As temperatures and pressures increase, new minerals are formed from the clay particles in pelitic rocks. Ions in crystal lattices of minerals are able to migrate and form different minerals even though no new elements are added from outside. Each mineral is characteristic of a particular temperature and pressure equilibrium. If geologists can identify these index minerals in metamorphic rocks they can say what the temperature/pressure conditions were when that rock was formed. We use the phrase high grade for minerals found in rocks which have reached high pressures and temperatures and low grade for those that have not been subjected to such high temperatures and pressures.
Look at specimens of the regional metamorphic minerals – chlorite, biotite, garnet, kyanite and sillimanite – to help you remember the order in which they form.
Read MET 4 on Metamorphic Minerals and create a poster or diagram which will help you learn the order of the index minerals.

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ACTIVITY 4 : LEARNING METAMORPHISM

TASK 9 PRACTICAL
There are 6 main metamorphic rocks – spotted rock, slate, schist, gneiss, marble, hornfels – that you need to be able to recognise in a practical exam.
Fill each practical sheet with a labelled pencil drawing to scale of a specimen of each of these rocks. Note how hard the rock is, because of its crystalline nature. Say whether you think that each rock is produced by heat or pressure or both.
You will probably be unable to recognise by tests and observations any of the minerals because they usually are too small for you to identify them even with a lens. Some rocks may have porphyroblasts. These are new crystals produced by the metamorphic process, which are larger that the average size of the crystals. Nevertheless you may need a lens to see them. Comment on the size of the crystals, the alignment (if any) and the colour of the rock. Check the composition with acid.
Margin notes / TASK 10 COMPOSITION OF THE MAIN METAMORPHIC ROCKS
Match each composition below with the metamorphic rocks you have described in Task 9.
a)  Pale or dark, flaky mica minerals in layers giving the rock a shiny appearance
b)  White or grey coarsely crystalline rock which may have coloured streaks and will fizz with dilute hydrochloric acid.
c)  Any rock with spots or crystals randomly arranged
d)  Extremely hard, finely crystalline rock often segregated into fine bands
e)  Grey, purple or green rock made of very fine clay particles which have been aligned so that the rock breaks along flat planes
f)  Hard, coarsely crystalline rock divided into different coloured bands of pale and dark minerals.
TASK 11 MICROSCOPE THIN SECTIONS OF METAMORPHIC TEXTURES
In class we will look at slides of rocks in thin section. The texture of metamorphic rocks allows geologists to understand the conditions of heat and/or pressure that the rock formed under. Be prepared to draw diagrams to show these metamorphic textures. Have your sharpened pencil, compass and ruler ready.
TASK 12 WHY IS METAMORPHISM SO DIFFICULT TO LEARN?
Suggest reasons in your group and make a list of the main difficulties. Then look at Fig 8.11 in MET 1 p 85. Explain why the diagram could be misunderstood. Make sure that you understand what it means by explaining it to a friend.
Deadline for test on metamorphism…………………………………..
TASK 13 TEST YOURSELF
Complete MET 1 Questions 1 – 9 p 86-87
Deadline………………………………………..
TASK 14 EXAM QUESTION PACK
Complete the Metamorphic Rock EQP
Deadline: ………………………………………
TASK 15 REVIEW NOTES
You need to learn this topic now.
Review notes deadline: …………………………………….

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ESTA GEOTREX The Geology Teachers Resource Exchange

Contributor: Alison Quarterman Establishment: Greenhead College Date:May 05

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