J-dek Flashcards
Hvordan kan vi få folding i de forskjellige strukturelle lagene:
- På/nær overflaten
- Midtre skorpe
- Nedre skorpe (undre)
På/nær: I sand, lava (ryolittisk)
Midtre: Leirstein, sandstein (10 km) og gneis (20 km)
Undre: Migmatitt (ca. 40 km), eklogitt (> 50 km)
Hva er den viktigste terminologien for folder?
- Vendepunkt, amplitude, bølgelengde
- Hengsellinje, hengselpunkt, foldesjenkel, åpningsvinkel, foldeakseplan
Hva er forskjellen på de forskjellige folde-formene?
Synform (U) og antiform (n) har ukjent stratigrafi.
Synklin og antiklin har kjent stratigrafi, og synklin har yngst lag mot midten.
Nevn de forskjellige åpningsvinklene en fold kan ha.
Isoklinal (30 - 0)
Tett (70-30)
Åpen (120 - 70)
Svært åpen (180 -120)
Hva er forskjellen på parallelle folder og similære?
Parallelle folder har konstant tykkelse på laget, mens similære folder har ikke.
Hvordan kan du kjenne igjen forskjellen på symmetriske og asymmetriske folder?
Symmetriske har ikke dip på foldeakseplan, mens asymmetriske har dip. Det vil si at asymmetriske folder har forskjellige foldesjenkler.
Hva er primære fabrics?
Sedimentære, magmatiske, salt-diapir
Hva er “tectonites”?
Rocks with a penetrative tectonic fabric
Hva er forskjellen på S og L tectonite?
S: Foliasjon dominert
L: Lineasjon dominert
Hva er foliasjon?
Any sort of planar or semi-planar fabric in a rock:
- Bedding, cleavage, schistosity, gneissosity
What is phyllites?
When lower green schist facies is reached, white mica and chlorite is formed. White mica contains more K and AL than illite and is better ordered.
Phyllitic cleavage is intermediate between slaty and schistosity.
What is schist?
Middle greenschist facies where coarser grained mica is formed. The resulting foliation is called schistosity.
What is gneissic layering?
At amphibolite to granulite facies conditions, where muscovite disappears and so does the schistosity.
Name some types of lineations.
Form lineations: Fold hinge, necks at buodins
Surface lineations: skjæringslineasjon, fiberlineasjon, striasjoner
Mineral lineasjoner
Name the three types of orogen styles.
Accretionary, collision and intracratonic
Name the two types of accretionary orogens with examples.
Retreating (modern Western Pacific) and advancing (Andes).
What is retreating (accretionary) orogen?
Western Pacific - type
- 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)
What is advancing (accretionary) orogen?
Andean type
- Overriding plate advances toward the downgoinf 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.
Difference between retreating and advancing?
Have different velocities of slab retreat rates.
Name 4 continent-continent.
- India-Asia (Himalaya)
- Laurentia - Baltika (Caledonides)
- Adria - Europe (Alps)
- E-W Gondwana
What happens during continent-continent?
Crustal thickening, with high-P metamorphism
Eventually delimitation of orogen root, asthenosphere upwelling meling, granites gravitational collapse
Hva er sammenhengen mellom temperatur og størrelse på orogen?
Large orogens are often hot, small orogens are often cold
Describe c-c of the Caledonides.
440 Ma: Retreating accretionary early history of Caledonides, volcanic arc outside Laurentia.
430 Ma: Collision of island arc terrane with Baltica.
420-410 Ma: Collision Baltica-Laurentia: Caledonides
What is orogenic gravitational collapse?
Orogens cannot grow in height forever, when a certain thickness is reached they tend to collapse under their own weight.
