Plate Tectonics Flashcards
Continental drift theory
All present day continents were once part of a single supercontinent (Pangaea)
Proposed in 1918 by Wegener
Wegener’s evidence
- continents fit together
- fossil evidence (same non-aquatic animals found all over world (matching it shows all the continents fit together))
- similarities in rock sequence (same thickness and order)
- pole wandering (WRONG) (pole wanders, continents move)
Plate tectonic theory
- rigid lithosphere floats on semi-rigid asthenosphere
- lithosphere is broken into plates (about 30)
- constant movement created by earth’s features
Layers of earth (top to bottom)
Crust
Mantle (lithosphere, asthenosphere)
Outer core
Inner core
Lithosphere
- rigid
- crust + uppermost mantle
- plate of tectonic plates
Asthenosphere
- part of solid mantle that flows (plastic flow (!))
- part of convection currents that move lithospheric plates
- semi rigid
- much denser than lithosphere and crust
What drives plate movement
Convection currents
What is subduction
One plate beneath another plate
Eastern Caribbean (St. Lucia, st. Vincent, etc)
- Caribbean + North American plates
- oceanic-oceanic
Andes
- nazca + South American plates
- oceanic-continental
Ring of fire
Pacific + lots
-oceanic-continental
Cascades volcanoes
- NA + Juan de fuca plate
- oceanic-continental
Himalayas
- india + Eurasia plates
- continental-continental
Appalachians
Ancient NA + Eurasian
-continental-continental
2 plates are now fused together
Results of oceanic-oceanic
Volcanoes
Small islands of big enough
Results of oceanic-continental
Mountains
Volcanoes
Results of continental-continental
NO SUBDUCTION
Mountains (both go up)
Sinai (Red Sea)
Eurasian + African plates
Divergent
Mid-Atlantic ridge
African + South American
Nor American + Eurasian
Divergent
African rift zone
African + Indian + Arabian plates
Divergent
Sam Andreas fault
Pacific + North American plate
Transform
Clarion fracture zone
Pacific + North American plates
Transform boundary
Alpine fault
Australian + pacific
Transform boundary
Hawaii
Hot spot
Pacific plate
Iceland
Between Eurasian and North American plates
Hot spot
Yellowstone
North American plate
Hotspot
Results of divergent boundaries
Plates pull away from each other (new crust)
Results of transform boundaries
-crust is neither produced nor destroyed as plates slide horizontally past each other
Results of hot spots
Constant hot pocket
Chain of volcanoes
Continental crust
Granite has big crystals (cool SLOW in dirt)
- Granitic rocks
- relatively lightweight minerals (Quartz + feldspar)
Ocean crust
Salt has small crystals (cool FAST in water)
- basaltic rocks
- denser + heavier
Continent + ocean
Continental on top (lighter)
Continental + continental
Both go up
Oceanic + oceanic
One goes under because they’re so heavy
Plate boundaries
- points where different plates meet
- most beneath oceans
- earthquakes and volcanoes concentrated there
Rift
- place where earth’s crust and lithosphere are being pulled apart
- NO new crust/lithosphere formed
French
Hemispheric long but narrow topographic depressions of sea floor
Ridge
New oceanic crust + lithosphere is created by seafloor spreading
NEW crust/lithosphere formed
Fault
Layers (cracks) in earth’s crust that are the result of different motion within the crust
How can we tell where the plates meet? (Land)
Volcanoes
Earthquakes
Mountains
How can we tell where the plates meet? (Oceans)
GEOSAY satellites map ocean floor
Craton
Ancient rock at core of continent
Terranes
Large block of lithospheric plate that has been moved and attached to the edge of a continent
Contributes to the growth of continents
cache creek Terrane in BC Canada
How to identify a terrane
- surrounded by major faults
- rocks and fossils don’t match those of continent
- magnetic record is different from continent
River sediments and continent growth
Sediments (eroded rock and soils) build up on edges of containers
Mississippi River delta
Igneous rock and container growth
Plutons formed from magma that rises beneath the surface and cools
Volcanoes at subduction boundaries eject lava, ash, rock materials (added to edge)
Chains of volcanic islands from subduction zones may be added
Modern evidence for plate tectonics theory
Arthur Holmes
- seafloor spreading
- Magma hardens + ferromagnetism - looking at rocks on sea floor shows pole flipping
