Last week there were a few comments that the Quiz on Structural Geology was not difficult enough – this week we have made it more of a challenge! Your challenge is to beat the GPTAPI that got 7/10 correct. Answers at the end.

1) What is a Durchbewegung texture?

1. A mixtures of silicate and competent sulphide clasts (commonly rounded) in a matrix of less competent sulphides
2. A texture formed by a fault and a thrust intersecting
3. The texture formed at the intersection between a crenulate cleavage and an axial planar fabric
4. A tripod of sticks used to support a billy for tea over a fire

2) What is an Allochthon?

1. A body of rock that has not been moved from its original position, usually in the footwall of a thrust fault
2. Imaginary surface that passes through all the hinge lines of a fold
3. A vein filled with mineral fibres, in which the fibres have grown outwards, toward the walls.
4. A body of rock that has been moved from its original position, usually in the hanging wall of a thrust fault

3) What is a C-plane?

1. Foliation in a shear zone, oriented oblique to the shear zone boundary, representing less deformed regions
2. A surface within a shear zone that is characteristically parallel to the zone boundaries and which shows the most intense deformation
3. Penetrative foliation defined by mineral grains coarser than ~1 mm.
4. A grid of curves, the 3-D equivalent of a protractor.

4) What are Antithetic Riedel shears?

1. Subsidiary fractures that form at about 75° to a fault, with sense of displacement opposite to that of the fault.
2. Three mutually perpendicular lines in a strain ellipsoid representing the maximum, minimum, and intermediate stretches
3. Linear fabric elements that are elongated, continuous domains
4. Subsidiary fractures that form at about 25° to a fault, with sense of displacement opposite to that of the fault.

5) What is a Décollement?

1. A very extensive flattening on a thrust fault, where there has been a large amount of movement.
2. A fold produced when wall rocks accommodate variations in slip between different parts of a fault.
3. A region of distortion between the tips of two faults, where slip is transferred from one fault tip to another.
4. Underwear commonly worn by an Adult Human Female.

6) What is a tensor?

1. A stress regime in which the minimum principal stress is vertical. Reverse faults are common.
2. A physical quantity that varies in magnitude with orientation, and can be represented by an ellipse or ellipsoid, or by a square matrix of numbers.
3. The line formed by the intersection of a geologic surface with the topographic surface or a cross-section.
4. A strike-slip fault that is also a plate boundary.

7) What is a forearc Basin?

1. A marine depositional basin on the trench side of a volcanic arc
2. A marine depositional basin on the oceanic side of an oceanic arc
3. A continental depositional basin formed on the continental side of a continental arc
4. A basin formed in an intracratonic rift

8) What are cusps and piercement cusps?

1. Platy or flake-shaped mineral grains
2. A vein where repeated cracking has occurred in the centre of the vein and mineral fibres are typically in crystallographic continuity with the grains in the wall rock.
3. Pinched-in folds at the interface between materials of different competency
4. The shape of a deformed circle that originally had unit radius.

9) What is a Sigma porphyroclast?

1. Sedimentary structures, such as flute and groove casts, preserved when coarse sediment is deposited rapidly on a muddy substrate
2. A high pressure tetragonal polymorph of quartz, in which silicon is in octahedral coordination, surrounded by six oxygen atoms.
3. A structure formed by foliation that sweeps around a porphyroclast forming curved, rhombic shape, indicating the sense of shear.
4. The envelope in 3D of all stresses (tractions) acting at a point.

10) What is vergence?

1. A physical quantity that has magnitude and direction, and can be represented by an arrow.
2. Change in position
3. The line formed by the intersection of a geologic surface with the topographic surface or a cross-section.
4. The direction in which rocks near the surface have moved relative to rocks deeper down.

11) Supplementary Question:  What is the texture in the above photograph

1. Massive banded sulphides
2. Flow banded sulphides
3. Crenulate cleavage developed in sulphides
4. Durchbewegung Texture

 

 

 

 

Answers:

1. A
2. D
3. B
4. A
5. A
6. B
7. A
8. C
9. C
10. D
11. D