GEOV104 strukturgeologi

Question 1

Name a primary structure

Answer 1

Cross-bedding

Question 2

What is stress?

Answer 2

It is force per unit area

Question 3

What is brittle deformation typical of?

Answer 3

Low temperatures and pressures in the upper crust

Question 4

Normal faults usually form in stressystems in which:

Answer 4

sigma 2 i horizontal (and 3)

sigma 1 is vertical

Question 5

A later fault will have the following relationship to an earlier fault:

Answer 5

The later fault will cut the older fault

Question 6

The length of a fault is usually roughly proportional to:

Answer 6

Maximum displacement on the fault

Question 7

What are components of deformation?

Answer 7

Rotation, translation and strain

Question 8

What is characteristic of homogeneous strain?

Answer 8

Straight and parallel lines remain straight and parallel

Question 9

What is true about relationship between strain and stress?

Answer 9

Strain CAN be proportional to stress (elastic)

Question 10

What effect does fluids have on rock strength?

Answer 10

Fluids decrease rock strength

Question 11

Where would cataclastic rocks generally tend to develop?

Answer 11

Along faults in the upper crust

Question 12

What types of fault systems tend to act as precursors to the separation of plates and the development of oceanic crust?

Answer 12

Rifts

Question 13

What fault geometries are characteristic of horsts and grabens?

Answer 13

Conjugate normal faults

Question 14

Why are earthquakes more likely to occur in the upper crust than in the lower crust?

Answer 14

The upper crust is dominated by brittle deformation

Question 15

What is true about rheology and rocks?

Answer 15

All rocks can flow

Question 16

Where do damage zones characteristically develop?

Answer 16

A damage zone is the volume of deformed wall rocks around a fault surface that results from the initiation, propagation, interaction and build-up of slip along faults

Question 17

Why is it important to show a hammer or person on field photographs?

Answer 17

for scale

Question 18

Geometric descriptors of geological structures include

Answer 18

orientation, dimension, shape and relationship

Question 19

Normal faults usually form in stress systems in which:

Answer 19

Normal faults typically form in stress systems dominated by tensional stress.

Question 20

There are two main types of strain:

Answer 20

Elastic strain: This is a temporary deformation where the rock returns to its original shape once the stress is removed. It’s like stretching a rubber band.
Plastic strain: This is a permanent deformation where the rock does not return to its original shape once the stress is removed. It’s like bending a piece of clay.

Question 21

Relay ramps occur at which locations?

Answer 21

Relay ramps occur specifically in the zones of normal faults. These are geological features where rock layers have been stretched and pulled apart.

Question 22

What is characteristic of ductile deformation?

Answer 22

-Extensive Plastic Strain: This is the most prominent characteristic. Ductile deformation involves significant permanent deformation of the rock before it fractures. Unlike brittle materials that crack readily, ductile rocks can bend, fold, and stretch considerably without breaking.
-High Energy Absorption

Question 23

Where can rocks be strongest?

Answer 23

Depth: Rocks tend to be stronger at greater depths because they are under higher confining pressure. This pressure helps to hold the rock together and prevents fractures from propagating.

Question 24

What is the best way to quantify the strain across a rift system?

Answer 24

Geological Observations:

-Offset Markers: Studying geological features like offset markers (rock layers, faults, etc.) that have been cut through by the rift can reveal the amount of displacement that has occurred.
-Tiltmeters: Instruments placed across the rift can measure slight tilts in the ground, which can indicate the direction and magnitude of tilting due to strain.

Question 25

What are the three fundamental mechanisms of folding?

Answer 25

Buckling, bending and passive folding.

Question 26

What is “buckling”?

Answer 26

Buckling or active folding can occur when a layer is shortened parallel to its length.
Buckling requires:
- A layer with higher competence or viscosity than its surroundings (matrix)
- Layer parallel shortening
- Plastic deformation.

Question 27

What is passive folding?

Answer 27

Passive folding involves passive flow of rock. Which means that there is no competence contrast, so layers serve as visual markers that passively flow with the rest of the rock.

Passive folds are similar (Class 2) folds, which maintain a constant thickness parallel to their axial surface.

Question 28

What is “bending”?

Answer 28

Bending can occur when forces act across the layering (bedding or tectonic foliation).

Bending is passive in the sense that folding does not initiate and grow as a result of competency contrast (no buckling instability). However, bending commonly involves layers of contrasting competence.

Ex.: Basement fault buried under sediments, and fault is activated - resulting in a monocline (forced folding).

Can also occur when salt or magma rise toward the surface. Badinage also generate forces that act across the layering.

Question 29

Name the important parts of folds:

Answer 29

Hinge line, fold axial plane, fold limbs, amplitude, wavelength, interlimb angle.

Question 30

What are foliations?

Answer 30

Planar structures that penetrate metamorphic rocks, and make rocks split into slabs and give deformed rocks exiting expressions.

Question 31

Define “tectonic foliation”.

Answer 31

Tectonic foliation is a general term about penetrative and cohesive planar structures in rocks that involve shortening across the structure. This is the general meaning of foliation as used by structural geologists.