GEOV104 strukturgeologi Flashcards
eksamen
Name a primary structure
Cross-bedding
What is stress?
It is force per unit area
What is brittle deformation typical of?
Low temperatures and pressures in the upper crust
Normal faults usually form in stressystems in which:
sigma 2 i horizontal (and 3)
sigma 1 is vertical
A later fault will have the following relationship to an earlier fault:
The later fault will cut the older fault
The length of a fault is usually roughly proportional to:
Maximum displacement on the fault
What are components of deformation?
Rotation, translation and strain
What is characteristic of homogeneous strain?
Straight and parallel lines remain straight and parallel
What is true about relationship between strain and stress?
Strain CAN be proportional to stress (elastic)
What effect does fluids have on rock strength?
Fluids decrease rock strength
Where would cataclastic rocks generally tend to develop?
Along faults in the upper crust
What types of fault systems tend to act as precursors to the separation of plates and the development of oceanic crust?
Rifts
What fault geometries are characteristic of horsts and grabens?
Conjugate normal faults
Why are earthquakes more likely to occur in the upper crust than in the lower crust?
The upper crust is dominated by brittle deformation
What is true about rheology and rocks?
All rocks can flow
Where do damage zones characteristically develop?
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
Why is it important to show a hammer or person on field photographs?
for scale
Geometric descriptors of geological structures include
orientation, dimension, shape and relationship
Normal faults usually form in stress systems in which:
Normal faults typically form in stress systems dominated by tensional stress.
There are two main types of strain:
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.
Relay ramps occur at which locations?
Relay ramps occur specifically in the zones of normal faults. These are geological features where rock layers have been stretched and pulled apart.
What is characteristic of ductile deformation?
-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
Where can rocks be strongest?
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.
What is the best way to quantify the strain across a rift system?
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.
What are the three fundamental mechanisms of folding?
Buckling, bending and passive folding.
What is “buckling”?
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.
What is passive folding?
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.
What is “bending”?
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.
Name the important parts of folds:
Hinge line, fold axial plane, fold limbs, amplitude, wavelength, interlimb angle.
What are foliations?
Planar structures that penetrate metamorphic rocks, and make rocks split into slabs and give deformed rocks exiting expressions.
Define “tectonic foliation”.
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.
