Surface and Internal Processes of the Rock Cycle Flashcards
Why do plate tectonic happen?
Rocks are put under stress
What stresses can rocks be put under?
Compression
Tension
What is stress?
The force applied to the rock
What is strain?
Give examples of strains
The way in which the rock reacts
Strain could be:
- snapping (fault)
- bending (fold)
- thinning (tension)
- thickening (compression)
Give the rock structures formed due to strain
Dipping
Folding
Faulting
What is dipping?
The plane orientation as the rocks all tilt one way
During dipping, which layer of rock is youngest and why?
The rock at the surface
- principle of superposition
What are the two types of fold?
Synform
Antiform
What do we call folds if they are the right way up?
Syncline
Anticline
What is te synform shape?
The sink, like a basin, U
What is the shape of an antiform?
Broken A, upside down U, n
Where are the rock ages in a syncline or anticline?
Syncline: youngest in the middle, oldest on the bottom
Anticline: oldest in the middle, youngest on the top
What do you call a fold that is the wrong way round but you know how old the rocks are?
Synformal anticline
Antiformal syncline
What are the features of a fold?
Hinge
Axial plane
APT
Interlimb angle
Fold axis
Limbs
What is the hinge of a fold?
Point where two limbs meet
What is the interlimb angle in a fold?
The angle between the limbs
What is the APT in a fold?
The point where the axial plane meets the fold
What are the names for the different angles in a fold?
> 70° = open
<70° = tight
Parallel limbs = isoclinal
What are the different attitudes of a fold axis?
Upright
Inclined
Overturned
Recumbent
What is competance?
The mechanical strength of a rock
What are the characteristics of competent rocks?
Give examples
RESISTS:
- erosion
- deformation
- folding
- faulting
E.G.
Metamorphic
Igneous
Limestone
Sandstone
Give the characteristics of incompetent rocks
Give examples
EASILY:
- deforms
- erodes
E.G.
Mudstone
Shale
What factors affect the way a rock responds to stress?
Competence of rock
Temperature
Speed
How does competence of rock affect the way in which a rock responds to stress?
COMPETENT = brittle and more likely to fault
INCOMPETENT = behaves more plastic more likely to fold
How does temperature affect the way in which a rock responds to stress?
HOTTER = more likely to behave plastically and fold
How does speed of stress applied affect the way in which a rock responds to stress?
FAST = more likely to fault
What is faulting?
Cracks in rocks along which movement has taken place
What are the two different types of fault?
Strike slip point
Dip slip
What is a strike slip point?
Rocks moving sideways along the fault
What directions can strike slip points move?
Dextral - moving right
Sinistral - moving left
What is a dip slip fault?
When the rocks move up and down relative to each other
How do we measure dip slip?
Throw and heave and angle of fault plane
What is throw?
What is heave?
Throw = vertical displacement
Heave = horizontal displacement
What are the 3 components in a dip slip fault?
Hanging wall
Foot wall
Marker bed
What is the foot wall?
The one on the bottom of a dip slip, the one you could theoretically stand on
What is the hanging wall?
The top one in a dip slip, you can’t theoretically stand on it
What are the two types of movement at a dip slip fault?
NORMAL - hanging wall goes down
REVERSE - hanging wall goes up
What is it called if the angle of fault plane in a dip slip is 45° or less?
THRUST
- always a reverse movement
What is the ‘map’ of an area?
view from above
What is the cross section of an area?
The view from the side if you sliced it open
What direction does the rock dip?
towards the youngest rock, so the one on the top
How do you draw a dip?
Line with a triangle pointing the direction of the dip
What is the line in the dipping symbol?
Strike
What is strike in a dipping symbol?
orientation at right angles to the dip
What is dip in a dipping symbol?
The direction the rocks are dipping
How would you describe a strike?
2 opposing compass points e.g. east-west
How would you describe a dip?
1 compass point e.g. south
What is an unconformity?
a boundary between 2 rock units which mark a gap in deposition
Describe an example of an unconformity forming
- original rocks laid down horizontally
- tectonic processes lead to faulting
- erosion wears away the surface
- a new period of deposition starts. The unconformity is the line between the two where it seems that two one type changes immediately into the next
