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41 terms

Plate Tectonics In-Class Test

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plate tectonics
study of formation & movement of earth's plates
lithosphere
crust & upper mantle - solid, brittle rock, behaves elastically (bends then breaks)
asthenosphere
upper mantle beneath lithosphere - exhibits plasticity due to great pressure
plate
solid section of Earth's lithosphere - Earth's broken into ~20 different plates that move in different directions
converge
plate interaction - moving towards one another
diverge
plate interaction - moving away from one another
rifting
divergence on LAND
sliding boundary
plate interaction - sliding horizontally past one another
convection
current w/ circular motion of material due to heating & cooling - ONE of the drivers of plate motion
upwelling
when magma moves up towards the surface
subduction
when ocean crust goes beneath less-dense continental crust, into the mantle
Alfred Wegener
1915, proposed that all continents were once joined in single land mass that started to break up ~250mil yrs ago
Pangaea
supercontinent that started to break up ~250mil years ago
Laurasia
Northern Pangaea
Gondwana
Southern Pangaea
EVIDENCE for continental drift #1 - puzzle
continents fit together like a puzzle - Atlantic coasts of SAmerica & Africa (when you examine the continental margins, they fit together even better)
EVIDENCE #2 - Fossil Evidence
fossils of plant & animal species of the same species found of different continents & no plausible explanation as to how they would cross 3,000mi of ocean - Mesosaurus
EVIDENCE #3 - Rock & Mountain Correlation
no two granites are completely the same (age & composition-wise) - Appalachians & Caledonian Mountains line up & are of the same comp ; identical rock composition & age in Maine & Northern Africa
EVIDENCE #4 - Glacial Evidence
glacial sediment deposits found in places where no glaciers are found today - glacial scratches line up like jigsaw puzzle when continents are reassembled
EVIDENCE #5 - Climactic Evidence
distribution of climate-sensitive sedimentary rocks on different continents - coal deposits found in Antarctica (coal forms in tropical climates from decayed organic matter - Ant. must have at one time been in a tropical climate)
response to continental drift theory
Wegener is RIDICULED! b/c... he was proposing a revolutionary proposal ; was a meteorologist, no respect there ; had no way to explain how plates were actually moving (tried to guess and say the tidal forces of the moon did it but he was wrong)
post-WWII submarine findings
ocean floor mapping 1940s, there are ridges in the middle of most oceans!
Mid-Atlantic Ridge
...a ridge in the middle of the Atlantic. Divergence. Seafloor spreading.
Harry Hess
1962 Princeton geologist, proposed SEAFLOOR SPREADING, centered on mountain ridges
seafloor spreading
as plates move away from each other, new ocean crust is created, plates powered by convection in asthenosphere b/c of divergence & upwelling ... as you move away from Mid-Atlantic Ridge, rocks get older
Why ICELAND is special
it's the only place on Earth where the Mid-Atlanitic Ridge is above sea level!
paleomagnetism
magnetic history of the Earth
polar reversal
about every 500,000yrs, magnetic poles switch when outer core moves in opposite direction
magnetometer
instrument Vine & Matthews used to detect magnetic orientation of minerals in rock - material spreading from oceanic ridge had a N-S-N-S pattern in a mirror image --> polar reversals
Curie point
580degC, temp at which magnetic minerals can no longer move and are magnetically solidified (if rock melted again, its "age" and magnetism would be reset)
hotspots
a plume of magma created deep within Earth around the mantle-core boundary - caused by unequal heating - rises towards surface helping to create volcanoes
Olympus Mons
CRAZY-HUGE volcano on Mars - no chain of volcanoes b/c Mars does not have plate tectonics
Hawaiian Islands
big island = largest, youngest b/c each island forms as plate moves over hotspot -- as islands age, they erode & become smaller
polar wandering
magnetic poles have stayed in ~same location - apparent polar wandering means the plates must be moving
formation of the Alps
movie! - alps formed ~30mil years ago, formed when Africa crunched into Europe and the oceanic crust initially between them buckled, forming jumble of Alp rock as high as 22,000ft (currently eroding away) - top of mountain=African rock ; middle mountain = oceanic rock ; lower mountain = European rock
primary crust
dates back to early solar system, emerged after Mars-sized object smashed into early Earth - some crystals of minerals separated early
secondary crust
forms after heat from decay of radioactive elements gradually accumulates within a planetary body
tertiary crust
forms if surface layers are returned back into the mantle of planet - yields light-colored igneous granties
Mohorovicic discontinuity
deep surface that marks radical change in composition to an extremely dense rock rich in the mineral olivine that underlies both oceans and continents everywhere
oceanic crust
basaltic composition
continental crust
granitic, rhyolitic composition