Ocean Basins Flashcards
What are typical features of a MOR environment?
Horst-graben structures
Ridge-parallel faults
Volcanism around 1-2km wide
Basalts leaking from fissure in rift valleys
What are the three types of MOR?
1) Fast-speading
2) Intermediate spreading
3) Slow spreading
What are sheeted dykes?
Many dykes parallel, side-by-side and separated by rocks
What can occur at a slow-spreading MOR?
Pluton dominated, because very little volcanism occurring. Altough the plate divergence does decompress the mantle, it does this slower so might not cross solidus to partially melt.
What are ophiolites?
Represent the top 10km of the oceanic crust
Form at MOR or BABs
Can occur as remnant oceanic crust in mountain belts after convergence (obducted)
What are the three major methods of ophiolite obduction?
- Overthrusting of OC onto passive-margin or arc rocks in continental collision
- Breaking off and overthrusting of the subducting slab
- Underthrusting of OC into accretionary prism.
What is the typical structure of oceanic crust?
From top down: Pelagic sediments Pillow lavas, on top of dykes Layered gabbros, gabbros Upper mantle (ultramafic)
Do ophiolites typically have a fast or slow spreading rate?
Fast
What are the chemical characteristics of MOR magma?
Primitive - around 50% wt Si
What are the two types of subduction zones?
Chilean - OC-CC
Mariana - OC-OC
What type of earthquakes occur at what depths?
- Shallow <50KM
- Intermediate <50-150KM
- Deep 150-700KM
What is the “transition zone” in the mantle?
The 660km discontinuity
What does subduction erosion occur?
High convergence rate (60mm/yr) plus low sediment supply rate. The overriding plate is eroded.
What does subduction erosion do?
Returns continental materials into the deep mantle.
Which plate do we assume is generally under contraction at a subduction zone?
The overriding plate
