SIO 30 Unit 3/4: Tectonic Plates

continental drift hypothesis

the idea that supercontinent Pangaea broke apart during the Mesozoic era and continents slowly drifted into their current positions (developed by Alfred Wegener in 1912)

seafloor spreading hypothesis

the idea that new oceanic crust forms through volcanic activity at mid-ocean ridges (gradually moves away); developed by Henry Hess

hotspot hypothesis

explains why volcanoes can form in the middle of tectonic plates; mantle plumes rise toward the surface, melting through crust (proposed by J. Tuzo Wilson)

plate tectonics theory

a combination of the continental drift and seafloor spreading hypothesis; explains that Earth’s lithosphere is divided into tectonic plates and these plates float on the asthenosphere (proposed by Wilson)

mantle convection current

temperature increases with depth; hot, less dense material rises to the crust while cooler, denser material sinks (continuous cycle)

terranes

squeezed/sheared during subduction to form plateaus, ocean ridges, etc.

super plumes

broad zone of mantle upwelling comprising return flow from subduction

divergent plate boundaries

new oceanic crust forms through upwelling, melting and magmatism; source of volcanoes/earthquakes

ocean-ocean divergent boundary

characterized through mid-ocean ridges

mid-ocean ridges

the area where rising plumes of magma from mantle convection lift, crack and separate plates

continent-continent divergent boundary

characterized through rift valleys

rift valleys

depressions with steep walls/flat floor; water fills the valley as it spreads

convergent plate boundaries

plates push together; this compression produces a buckling/shortening (subduction); produces earthquakes/volcanoes

ocean-continent convergent boundary

characterized through subduction; oceanic crust subducts under continental where a trench forms and crust melts from H2O/CO2 release, forming volcanoes

ocean-ocean convergent boundary

characterized through subduction; older oceanic crust subducts; sinking crust deforms into deep trenches, produces island arcs

continental-continental convergent boundary

characterized through mountain building; both plates are about the same density so neither subduct (instead it goes up)

transform plate boundaries

plates shear/slide laterally, neither destroying or creating crust; characterized through intense seismic activity (earthquakes)

passive margins

Atlantic-type margins characterized through broad continental shelf/gentle sloping; produce very little volcanic/earthquake activity

active margins

Pacific-type margins characterized through narrow continental shelf/steep sloping; located near edges of converging plates and produce a lot of volcanic/earthquake activity

magnetic stripes

alternating bands of normally/reversely magnetized rocks found on ocean floor (provides evidence of seafloor spreading/plate tectonics)