5. Fold Mountains Flashcards
What is deformation?
Deformation occurs when rocks change size or shape due to stresses
What is compression?
Compression is when rock is squeezed or shortened, usually at convergent plate boundaries. Compression results in folding or faulting in the rock
What is rock tension?
Tension is when rock is stretched and thinned, usually at divergent plate boundaries. It often results in faulting in the rock
What rock shearing?
Shearing is when rock is moved sideways in opposite directions, usually at passive or convergent boundaries. It results in shearing and faulting in the rock
What is folding?
Folding is the process in which the earths crust is deformed
What is the anticline?
The part of the fold that has been folded upwards
What is the syncline?
The part of the fold that has been folded downwards
What are the limbs of a fold?
The part that connects the anticline and the syncline
What is a symmetrical fold?
This has two limbs of equal steepness as a result of compression being applied equally from both sides
What is an asymmetrical fold?
This has one limb steeper than the other as a result of greater compression applied to one side of the fold
What is an over fold?
This has one limb pushed over the other limb as a result of greater compression applied to one side of the fold
What is a recumbent fold?
As the compressional forces continue, the limbs become almost parallel to each other and begin to move in the same direction
What is an overthrust fold?
As the compressional forces continue, the force becomes so great that the rock on one side fractures, pushing one limb on top of the other. As a result, the strata in the rock are no longer continuos
What are compressional forces?
They heat the rock making it ductile- this means the rock can be folded and bent without breaking
What is orogeny?
• The process of fold mountain building is referred to as orogeny
What does orogeny result in?
Orogeny results in intense deformation of rock and is usually accompanied by faulting,
metamorphism and plutonic activity.
What are the three main periods of orogeny?
Caledonian, Armorican and Alpine
Caledonian Orogeny
- Caledonian mountain ranges
- 400 mya
- N.America and Eurasian collide
- e.g Dublin/Wicklow Mtns
- overlying sedimentary and underlying igneous broken down by denudation
Armorican Orogeny
- 250 mya
- African and Eurasian plates collide
- e.g Macgillycuddy’s Reeks in Munster Ridge
- not been exposed to as much weathering and erosion
Alpine orogeny
- Alps, Himalayas, Andes
- 60 mya till today
- e.g Mount Blanc, France, 4809m
Mt Everest, Nepal 8848m
Mt. Aconcagua, Argentina 6959m - didn’t impact Irish landscape
