Oceanic Lithosphere Flashcards
what is the average depth of the seafloor?
around 4000m
no light below around 200m
how much of the earths surface is the ocean floor?
70%
where is oceanic lithosphere created?
at MORs
where is oceanic lithosphere recycled back into the mantle?
at subduction zones
how old is oceanic lithosphere?
less than 200Ma
how do we study the ocean floor?
(1) Look at and sample it with submersibles:
- Remotely operated vehicles (ROVs)
- Manned submersibles
(2) Sample rocks from the subsurface using drill ship
- Drill cores provide information about the ocean crust over millions of years of the Earth’s history
(3) Study ‘ophiolites’: exposures of ocean crust rock now on lan
what are the components of seafloor topography?
continental margin (shelf and slope)
abyssal plain
MOR
what are the dominant sediments on the seafloor?
terrigenous
clay
siliceous ooze
carbonate ooze
how deep are abyssal plains?
3 to 6 km deep
what types of tectonic and volcanic activity are there on abyssal plains
very limited
where do fine sediments accumulate from on abyssal plains?
form water columns
what do abyssal plains look like? what type of life is there?
Crinoids or “sea lilies”
sea cucumbers
Tracks and trails (left by seafloor organisms)
what are MORs (in the context of oceanic lithosphere)?
Continuous ridges over Earth’s seafloor
2500 m above surrounding seafloor
Central rift valleys locally filled with basalt flows - volcanism in a narrow zone
what happens at MORs?
oceanic lithosphere
(1) Seafloor spreading: forms new oceanic lithosphere
- Most active volcanism on Earth
- ‘passive’ rise of solid mantle rock -> decompression melting -> magma
- magma erupts at surface -> creates new ocean crust
(2) Hydrothermal activity
what is the hydrothermal activity at MORs?
New basalt rock formed by magma eruption is porous
- > seawater circulates through the rock -> hydrothermal metamorphism ->greenstone (recall)
- > water heated at base of system, leaches metals, exits at vents
- > precipitate metal sulfides at ‘black smokers’ – build “chimneys” as high as skyscrapers
- > sources of life
350 deg. C , metal-rich fluids exit the seafloor at mid-ocean ridges
Hydrothermal fluids support unique ecological communities that use chemicalenergy (chemosynthesis)
