L8: Structural Geology Basics

Question 1

Brittle vs Ductile

Answer 1

Defines if rocks will break or bend under deformation

Usually, temperatures allowing for bending happen at 10-15 km depending on the rheology of the rock.

Question 2

Rheology

Answer 2

Strength of rock

Question 3

3 types of deformational forces and their faults

Answer 3

Compressional - Pushed together; collision zones; reverse faults
Tensional - Pulled apart; normal faulting; occurs at rifts and mid-ocean ridges
Shearing - Sliding past each other; strike-slip faults; conservative boundaries

Question 4

Dextral vs sinistral strike-slip faults

Answer 4

Dextral - right displacment

Sinistral - left displacment

Question 5

Throw and Heave in normal and reverse faulting

Answer 5

Throw is the vertical displacement

Heave is the horizontal displacement

Question 6

Horst and Graben

Answer 6

When normal antithetic faults have their dips facing the block between them slips and forms a basin called a Graben
When normal antithetic faults have their dips facing away from each other this forms a topographically high block between them called a horst

Question 7

Reverse faults

Answer 7

• When there is a compressional fault, occurs in collision zones and subduction zones
• Causes thickening of crust
• Hanging-wall is pushed up (against gravity).
• Less than 30 degrees are thrusts
• Rollover anticlines are formed.

Question 8

Normal faults

Answer 8

• When there is a tensional fault; occurs in rifts and mid-ocean ridges
• Causes thinning of the crust
• Hanging-wall slides down (aided by gravity)
• Younger faults develop in the hanging-wall.
• Steep angles of 60 degrees are common.
• When multiple faults occur domino faults occur as the blocks rotate and listric faults are curved and concave upwards

Question 9

Fold axis

Answer 9

Line of maximum curvature in a fold

Question 10

Fold limbs

Answer 10

Rocks either side of the axis

Question 11

Axial plane

Answer 11

Fold axis of multiple layers joined

Question 12

Antiform

Answer 12

Upwards fold

Question 13

Synform

Answer 13

Downwards fold

Question 14

Recumbent fold

Answer 14

Sideways fold

Question 15

Symmetric fold

Answer 15

Same both sides

Question 16

Asymmetric fold

Answer 16

One limb is shorter than the other

Question 17

Anticline

Answer 17

Oldest rocks in the middle

Question 18

Syncline

Answer 18

Youngest rocks in the middle

Question 19

Isoclinal folds

Answer 19

So tightly folded limbs are parallel

Question 20

Chevron folds

Answer 20

Straight limbs with sudden change

Question 21

Anatexis

Answer 21

Partial melting of rocks in the crust