The Ocean Crust Flashcards
Ocean crust
- the result if partial melting of the mantle
- symmetrical magnetic anomalies in the ocean give dates for the age of the crust
- lithosphere consists of upper mantle and the ocean crust
- all ocean crust is younger than 180 million years
Mid-ocean ridge
- an underwater mountain system formed by plate tectonics. It consists of various mountains linked in chains
- there is often a shallow magma chamber
Iceland
- crustal spreading and rifting
- an additional plume which lifts area of crust
- lies over a mid-ocean ridge
submarine pillow lavas
- lava coming out of crust and instantly chilled when in contact with water
Vesicular basalt
Rock type, much of the magma contained lots of gases, which biol out and for bubbles/holes within rock type
Sheeted dykes
ultrabasic rock in mantle moves upwards,
- these layers are injections of material causing plates igneous origin
The crust
- 5-70 km thick
- Vp = 3-7 km/s
- continental crust: felsic, granite 70%
oceanic crust: mafic, gabbro/basalt 50%
Gabbro and basalt features
Basic igneous rocks
- normally dark colours
- specific density of 2.8-3.1
- mineral (Pyroxene, palgioclase Feldspar, also olivine etc. in smaller amounts)
- Overall contain 45-52% SiO2 and are high in iron and magnesium
ocean topography
- controlled by thermal contraction
- deep marine sediments accumulate over the ocean crust
lithosphere
is the cold conducting slab above the convecting asthensosphere
the boundary is at about 700oC
Transform faults
Types of strike-slip faults that join other tectonic elements, e.g. between segments of mid-ocean ridge
Gabbro
coarsely crystalline, slow cooled, intrusive (plutonic)
Basalt
finely crystalline (may not be visible with naked eye) often cooled quickly, extrusive lavas
Sea floor spreading
- doesn’t occur equally through he ridge
- averages around 4 cm a year
