Tectonics: The Plate Boundaries Flashcards
 How do mid ocean ridges occur
Manta rises, below surface,
pressures, lowered, decompression, melting
Rocks partially melt.
Plumes of magma, melt the crust above, crust expands on heating and up domes
split and volcanism begins convection currents in the way is the cost as a moves away from rift causes, lateral tension results in parallel faulting. Allow central section to subside into magma, creating a rift Valley
How is a new ocean formed?
plates move further magma cools form basaltic ocean crust, causes, seafloor, spreading and ocean.
Basin gets wider as rift continues. Seawater floods in to create an incipient sea
Evidence for seafloor spreading
Magnetic properties of the erupted basalt
earths magnetic field have been shown to flip occasionally so north and south pole swap
salts contains minute magnetic minerals and this changes directions depending on the earths magnetic field at the time of eruption 
magnetic stripes
Polarity reversal from rock formations at the, mid-Atlantic ridge 
Why do earthquakes occur at divergent plate boundary?
New Cross forms and spreads causes transform fault right angle two plate boundary
Move at different times. Friction causes plates to lock and buckle causing earthquakes. 
How do volcanos form?
as plates move apart - decompression melting - magma rises and starts melting the crust - and forms a volcano - usually oceanic crust = basaltic lava = shield volc
but nubia and somalian - continental so andisitic lava
descibe what a transformative / conservative plate is like
parallel movement of plates - differents speeds or/and directions - e.g. San Andreas Fault in Cali
describe the san andreas fault
btw N. Americ ad Pacific
1300 km
right lateral strike slip fault
fault system visible and cause 10,000 earthquakes a yr
why do earthquakes occur at conservatives
plates move sporadically and jerkily - frictional forces lock plates into eachotehr - friction builds up pressure strain and heat - suddenly releases energy - causes shallow focus earthquakes
Plate movements in o + c convergence
Denser, oceanic subducts
Tectonic processes in o + c convergent
Subduction and slab-pull
hydration melting
stoping (burning)
folding and faulting
friction and strain release
Landform o + c convergence
Composite volcanoes, ocean, trenches, fold mountains, volcanic arcs 
How do you trenches form - o + c convergence and example
As oceanic subducts, a deep V shaped depression is formed e.g. Mariana trench 
How do earthquakes form o + c
Subduction is not smooth + friction friction = strain = builds up pressure which is released when the plate slips releasing seismic waves.
What kind of earthquakes o+ c
Shallow to deep focus in the zone of earthquake foci - Wadatti-Benioff Zone
often high magnitude, 8 - 9 
How do you fold mountains occur? E.g
As oceanic subducts said, sediment accumulate on ocean floor - scraped off and forced onto the continental plate, due to obduction - forms in accretionary wedge - adds to size of continent
Collision —> Crustal shortening leads to vertical thickness and reducing the width of the lithosphere collision zone. fold and faulting rocks form in the fold mountains
E.g. the Andes
magma generation o + c
O subducts - when reach Benioff zone,
oceanic plate starts to crack and waters dragged out. This lowers the melting point of the magma (dehydration, melting) which generates magma.
How are volcanoes formed o + c
Magma rises up to Fischers and freeze doping till they reach the surface. They melt some of the continental plates on its way up, making making it silica rich, causing andesitic lava. - this causes composite volcanoes
When explode cause release pyroclastic, flow, ash and gas 
Describe andesitic lava
800 to 1000°C. High viscosity from is composite volcanoes. VEI 5-6
How do you tsunamis occur?
Earthquake magnitude greater than six call seafloor to uplift causes a vertical displacement of water. This causes a tsunami. Low lying wave until close to
shore, it starts to grow into a taller wave.
What happens in oceanic and oceanic convergence? E.g
Denser colder, oceanic plate subducts, this causes, submarine volcanoes, which, if grown, can cause volcanic arc. Lava can also produce island arcs.
E.g. Caribbean and South American plate
Landforms in oceanic and oceanic convergence
Composite volcano, ocean, trench island arc

Continental continental convergent
Two seas collide sediment exist between plates are pushed into each other and upwards, folding + faulting to make fold mountains
cause strain to build up when energy is released cause shallow, intermediate earthquakes, 6-8 magnitude 
Example of continental continental convergent
Eurasian, and Indian plate forms the Himalayan mountains
Geosyncline (basin) was sea of Tethys which eventually subducted and filled with sediments which was obducted
