lecture 4 Flashcards
who suggested continental drift
alfred wegener
3 evidence that lead to continental drift
- continuities in mountain ranges on opposite sides of oceans
- similarities of fossil land animals seperated by oceans
- glacial striations
mechanism behind continental drift
plate tectonics- lithosphere is divided into rigid planes whos motion is driven by convection of the underlying spheres (convection in the mantle)
where is the lithosphere created
divergent boundaries
where is the lithosphere consumed or thickened
convergent boundaries
where is the lithosphere translated
strike-slip boundaries
sea-floor spreading
magma erupts at the ridge axis creating a new oceanic crust and pushes aside older crust
sea-floor striping
basalt erupted at mid-ocean ridges over millions of years preserves symmetric pattern of magnetic anomalies
geomagnetic reversal
flow patterns of the core are unstable and the field is shifting, at random intervals the magnetic poles swap places
radiometric dating
allows us to assign ages to the magnetic stripes and date oceanic crust
subduction zone
process by which slabs of old oceanic lithosphere are consumed beneath more buoyent lithosphere
- starts at a trench and proceeeds beneath a volcanic arc
why does volcanism at subduction zones occur
addition of water to the mantle from wet sediments in the subducting slab
water lowers the solidus which touches the geotherm
- melt is produced at a lower temperature than normal
continental collision zone
once oceanic lithosphere between two continents is subducted, they collide
why cant continental crust be subducted
it is too buoyant and instead it thickens the lithosphere and forms a mountain range
continental rifts
divergent plate boundaries exist between continental plates
