2.18 Faults

Question 1

What is a fold?

Answer 1

a flexure in rocks, where there is a change in the amount of dip of a bed

Question 2

What type of force creates folds?

Answer 2

all folds are produced by compressive forces acting horizontally

Question 3

What type of tectonic settings are folds created at?

Answer 3

folds are associated with convergent plate margins

Question 4

What is an antiform?

Answer 4

an upward closing fold

Question 5

What is a synform?

Answer 5

a downward closing fold

Question 6

What is an anticline?

Answer 6

an upright fold with the oldest rocks in the core

Question 7

What is a syncline?

Answer 7

a downward pointing fold with the youngest rocks in the core

Question 8

What is the hinge of a fold?

Answer 8

the line along which there is a change in the amount and/or direction of dip, forming the most sharply curved part of the fold

Question 9

What is the limb of a fold?

Answer 9

the section of a fold between one hinge and the next, forming the side of a fold

Question 10

What is the axial plane of a fold?

Answer 10

a plane that joins the hinges of all the beds - it bisects the fold

Question 11

What is the axial plane trace?

Answer 11

the outcrop of the axial plane at the Earth’s surface

Question 12

What is the name for a fold with an inter-limb angle of between 180 and 120 degrees?

Answer 12

gentle

Question 13

What is the name for a fold with an inter-limb angle of between 120 and 70 degrees?

Answer 13

open

Question 14

What is the name for a fold with an inter-limb angle of between 70 and 30 degrees?

Answer 14

closed

Question 15

What is the name for a fold that has a vertical axial plane and limbs that have the same dip?

Answer 15

symmetrical or upright

Question 16

What is the name for a fold where the axial plane dips and the limbs have different dips?

Answer 16

asymmetrical or inclined

Question 17

What is meant by the term plunge when referring to a fold?

Answer 17

the angle of dip of the axial plane from the horizontal

Question 18

How can a plunging fold be identified on a map?

Answer 18

plunging folds form a U- or V-shaped outcrop pattern on a horizontal surface

Question 19

What is a dome?

Answer 19

an anticline which dips away from the centre in all directions

Question 20

What is a basin?

Answer 20

a syncline which dips away from the centre in all directions

Question 21

What is an overfold?

Answer 21

folds which have both fold limbs dipping in the same direction but by different amounts

Question 22

What is a recumbent fold?

Answer 22

a fold that has an axial plane and fold limbs which are close to horizontal and always less than 30 degrees

Question 23

What is a nappe?

Answer 23

a fold that has been broken (faulted) along a thrust plane

Question 24

What is an isoclinal fold?

Answer 24

a fold that has parallel limbs that are nearly vertical and in very tight folds

Question 25

What is a joint?

Answer 25

a fracture in a competent rock along which no observable movement has taken place

Question 26

What is a cross joint?

Answer 26

joints at an angle to the axial plane trace of the fold

Question 27

What is a tension joint?

Answer 27

a joint that is parallel to the axial plane trace of the fold