oceanic lithosphere/building continents

oceanic lithosphere (creation/age?)

created at MORs, recycled back into mantle at subduction zones. <200 MYO

what happens at MORs?

1) sea floor spreading forms new oceanic lithosphere

2) hydrothermal activity (greenstone and “chimneys”)

3) seafloor deepens around them (as a function of rock age)

black smokers

hydrothermal vents in the sea floor that shoot out mineral rich water

3 ways we study the sea floor

1) submersibles

2) sampling rocks from drilled cores

3) studying ophiolites

ophiolites

bits of oceanic plate that ended up on land. a detailed x-section that can be studied

5 layers of an ophiolite/the seafloor

1) sediments

2) pillow basalts

3) sheeted dikes

4) gabbro (frozen intrusive magma chamber)

5) mantle rock (peridotite/olivine?)

bathymetry

topography of the sea floor

sea floor (how much surface/how deep on average)

takes up 70% of earth’s surface, avg depth: 4000 m

abyssal plains

areas of deep sea floor with limited tectonic activity

younger plates subduct ___ (shallower/deeper)

shallower

isostasy

the state of gravitational equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density

isostatic adjustment

loading of mass (eg ice sheets) increases load and causes lithosphere to sink. erosion/melting of mass causes lithosphere to uplift

wilson cycle

the cycle of oceanic basins opening up and then closing

continents

all areas underlain by continental crust (continental land areas and the continental shelf)

how are continents built

1) igneous materials at a volcanic arc

2) accretion at the edge of continents (from subducting plate)

3) collision of plates builds mountains