module 4/5- plate techtonics Flashcards
why is earths surface constantly changing
-earth is dynamic. wind water and ice erode and shape the land
- volcanic activity and earthquakes alter the landscape in a dramatic manner. Movement of earths plates slowly reconfigures oceans and continents. internal and externl heat
- internal- melts rocks, volcanoes, moves continets
- external: creates climate and weather, controls erosion and eposition
who were the scientists primaryliy responsible for the development of the plate techtonic theory
alfred wegner in 1912: published ideas on continential drift
what is our current understanding of plate techtonics
-plate tectonic theory: earths surface is divided into a series of large plates that move, allowing continents to change positions.
- super continent pangea. continential shapes fit into eachother
what scientific evidence is techtonic plates based on
- fossils: similar ones found on different continents, on both sides of atlantic
- glacial depostits of gondwana- glacial sediments around same age on south america, africa, antarca, india, austrilia
- sonar helped prove. sea floor mountains formed by plate tectonics. used geomagnetism to help prove that sea floor created MOR’s reabsorbed into mantle at trenches
what is paleomagnetism and how has it been used to validate the theory of plate tectonics
- magnetic reversals documented for the past 330 million years
- approx every 300,000 years
last one approx 780,000 years ago
-study of magentic fields fixed in rock
how old is the sea floor
on average 200 million years old
what processes operate at plate boundaries
- many different things
- MOR’s
-divergent, convergent, transform plate boundaries - earthquakes
Mid Ocean Ridges
seafloor mountain system formed by plate tectonics
divergent plate boundaries
- plates move away from each other
- in ocean or on continent
-create new ocean basins/ new ocean crust - involves: thinning, rifting, and extension
- associated with volcanoes (basaltic lavas) and shallow focus earthquakes
- EX. red sea, iceland
convergent plate boundary
- two plates moving towards eachother
- different scenerios: ocean-ocean, continential-continential, ocean-continetial
-associated with shallow, intermediate, or deep earthquakes - partial melting creates andestic magma, explosive volancoes, eg. Mount st helens
-creates mineral deposits (ring of fire)
-andes mountain range
ocean continential
-oceanic plate subducts the continental plate because the oceanic plate is denser and therefore subducts
ocean ocean convergence
- more dense plate descends (older, colder plate)
- form deep trenches (ex. tonga trench)
- island arc volcanoes (ex. japan, phillipines)
- pacific ocean rimmed with convergent margins; volcanoes and earthquakes common; called the ring of fire
continetnial continential
- continential crust does not subduct because it is too buoyant
- a mountain belt forms along suture between continental continential (ex. himalayas)
- plates crumple and form mountain ranges- land folds upwards
-this process is obduction - mountains keep forming until plates move another way (takes long time)
- ex collision of India with Eurasia.
transform boundaries
- plates move horizontally past eachother
- associated with shallow focus earhquakes
- ex. san andreas fault (1200 km long)
- often link sections of divergent or convergent margins
why do we need to know the plate tectonic histpry of N America
- N america consists of many small micro-continents (proviences) joined together
- joints ( or sutures) are areas of weakness in the crust which are potential sites for future earthquakes
- hamilton lies close to an old suture zone in shield (Central Metasedimentary Belt Boundary Zone)
- this is a weakness in crust and a potential earthquake cite
- we need to know these things so we know where we can/cannot build things. ex. a nuclear power plant was built on old suture zone in pickering. earthquakes more common here. not good to build nuclear power plant here because if earthquake occurs, nuclear material could harm surrounding environemtns
