Terminology Flashcards
Primary structures
Structures related to sedimentology or igneous processes
Secondary structures
Features formed by tectonic processes, e.g., folds, faults, veins, joints, diapirs, etc.
Normal faults
Hanging wall moves down + missing section
Reverse faults/thrusts
Hanging wall moves up + repeated section
Strike-slip faults
lateral/horizontal movements (no hanging wall)
Stress
Force per unit area. Stress is a vector, having a magnitude and orientation.
Strain
The deformation that results from applied stress
Fold limb
Foldesjenkel - “armene” til folden
Hinge line
Linjen hvor foldesjenklene møtes
Foldeakse
“Enden” på hengsellinjen
Fold axial plane
Planet som går gjennom midten til foldesjenklene, kan brukes for å se vergence.
Synform
Ukjent stratigrafi, smilefjes
Antiform
Ukjent stratigrafi, surt fjes
Accretionary orogen
Orogenesis during on-going subduction, can be divided into two types; retreating orogens and advancing orogens.
Retreating Accretionary Orogens
- Long term extension in response to lower plate retreat
- Driven by negative buoyancy of down going slab
- Trench rollback
- Develop back-arc basins, upper plate extension
- Rifting of continental ribbons
- Magma can rise directly to the surface (mafic-felsic, bimodal)
Advancing Accretionary Orogens
• Overriding plate advances towards the downgoing plate at rate equal or greater than the rate of lower plate slab retreat
• Widespread crustal shortening and uplift
• Resulting in a foreland fold and thrust belt
• Strike-slip motion common
• Subduction erosion: accretionary prism
• Large earthquakes
• Slow magma-rise: since fractures are
closed; causes large fractionation: intermediate to felsic rocks
Shear sense indicators
Mica fish, S-C-structures, grain tail complexes; sigma, delta and phi
