A: Geological Structures

Question 1

What are geological structures?

Answer 1

Structures are variations in the properties of the Earth’s crust.

Question 2

What are the 2 broad classes of structures?

Answer 2

Spatial variations: the rocks of the Earth’s crust vary from place to place, either on the surface or below; or
Directional variations: rocks look different when viewed from different directions.

Question 3

What is a geological boundary?

Answer 3

where one type of rock contacts another, includes: faults
bedding planes
the edges of igneous intrusions (intrusive contacts)
ancient erosion surfaces (unconformities)

Question 4

What does fabric mean?

Answer 4

Any penetrative structure that gives a rock different properties in one direction relative to another, e,g. mineral alignment

Question 5

What are primary structures?

Answer 5

A geologic structure formed at the same time as the rock in which it is found. Examples: beds, laminae, lava pillows

Question 6

What are secondary structures?

Answer 6

A structure formed well after the rock in which it is occurs. Example: folds, fractures, foliations. Often caused by deformation

Question 7

What is deformation?

Answer 7

The movements of parts of the Earth’s crust relative to each other.

Question 8

What does tectonics mean?

Answer 8

The mathematical study of structures; commonly applied to large-scale movements of the lithosphere and the structures that these have produced (plate tectonics).

Question 9

What is plate tectonics?

Answer 9

A theory describing the large-scale movements of the the lithosphere using simple mathematical and geometrical methods to describe the movement of rigid plates.

Question 10

What are the 3 main types of structural analysis?

Answer 10

1. Descriptive or Geometric
2. Kinematic
3. Dynamic

Question 11

What is Geometric analysis?

Answer 11

what are the positions, orientations, sizes and shapes of structures that exist in the Earth’s crust at the present day?

Question 12

What is kinematic analysis?

Answer 12

what changes in position, orientation, size, and shape occurred between the formation of the rocks and their present-day configuration?

Question 13

What is dynamic analysis?

Answer 13

what changes in position, orientation, size, and shape occurred between the formation of the rocks and their present-day configuration?

Question 14

What is strain?

Answer 14

Change in size and shape (dilation and distortion).

Question 15

What is stress?

Answer 15

Force concentration or force per unit area; also, the concentration of all the forces acting at a point within the Earth.

Question 16

What are the 3 main scales that we use?

Answer 16

Microscopic structures are those that require optical assistance to make them visible.
Mesoscopic, or outcrop-scale structures are visible in one view at the Earth’s surface without optical assistance.
Macroscopic, or map-scale structures are too big to see in one view.