Plate Tectonics Theory Flashcards
Asthenosphere
Part of the Earth’s mantle that lies below the lithosphere, at depths between 100-700 km
Conservative plate margin
A plate margin where two tectonic plates are moving past one another with no addition or destruction of plate material.
Constructive plate margin
A plate margin where new crust is generated as the plates pull away from each other. These are found at mid-oceanic ridges.
Destructive plate boundary
A plate margin where the crust is destroyed as two plates converge. These are associated with island arcs and young fold mountains.
Paleomagnitism
A record of the history of the Earth’s magnetic field, preserved in magnetic materials in volcanic rocks.
Plate tectonic theory
The theory states that the Earth’s crust is made up of several rigid plates moving relative from one another.
Plume
A hot column of magma which rises from deep within earth.
Rift Valley
A long, deep valley is found in the centre of a spreading ridge. It is formed between parallel faults where a block of the crust has sunk.
Sea floor spreading
The theory is that the ocean floor is moving away from the mid-oceanic ridge and across the deep ocean basin, to disappear beneath continents and island arcs.
Tectonic plate
One of a series of rigid sections of the Earth’s crust. They float on the upper mantle and move relative to one another.
Differences between oceanic and continental crust- thickness
Oceanic= 6-10km
Continental= 30-70km
Differences between oceanic and contiental crust- age
Oceanic= less than 200 million years
Continental= over 1500 million years
Differences between oceanic and continetal crust- density
Oceanic= 3.0 (heavier)
Continental= 2.6 (lighter)
Differences between oceanic and continental crust- composition
Oceanic= mainly basalt; silicon, magnesium, oxygen
Continental= mainly granite; silicon, aluminum, oxygen
Evidence for plate tectonics- continental fit
Jigsaw fit of continental shelves proved that they were once joined together
Evidence for plate tectonics- fossils
Fossils of similar species are found in South America and South Africa- must have been joined
Evidence for plate tectonics- climate zones
certain places experienced ice ages when their location would deem that impossible
Evidence for plate tectonics- geology
Rocks of similar composition are found in different places. identical rocks found in opposite locations which means they once formed side by side.
What happens at destructive plate margins and what events are they associated with
-Destructive margins happen when the oceanic plate slides beneath the continental plate
-Crust is destroyed as one plate dives under another at the subduction zone.
-The rocks catch against each other as the plates are not smooth.
-The pressure between the plates builds until the plates cannot take the stress.
-The plates slip past each other which can cause both plates to move, resulting in the ground shaking.
What happens at constructive plate margins and what landforms are they associated with
-They ‘construct’ to form a rift valley when land is pulled apart
-At constructive plate margins, the plates move apart (diverge)
-The convection currents diverge and cause a gap between the plates
-Magma rises up and fills the gap that is created
-New crust is created as the plates pull away from each other.
-Rift valleys are created when the crust pulls apart and land drops to create a valley.
What happens at conservative plate margins
-At conservative plate margins, plates are sliding past one another horizontally, crust is neither produced nor destroyed
-The plates are made of rock that has jagged edges so they catch and snag against one another.
-Friction and pressure between the plates build until the plates can’t take the stress.
-The plates slip past each other, which can cause both plates to move resulting in the ground shaking.
Summary of 3 types of plate margins
-Destructive- oceanic plate slips past continental plate, one plate subducts beneath the other, causing shaking
-Constructive- plates diverge (move apart) causing a gap, magma rises and rift valleys created
-Conservative- plates slide past eachother horizontally friction and pressure building, causing shaking
What are plate margins
Where tectonic plates meet
Briefly highlight earths structure
-Earth’s structure is composed of 6 layers each of varying thickness and viscosity: the crust, lithosphere, asthenosphere, upper and lower mantle, outer core and inner core.
-The crust is thin and rigid averaging 30km in depth (from 5km beneath oceans to 100km beneath mountains)
-Mantle is a dense hot layer of semi-solid sock, 3000km thick- split into upper and lower mantle.
-The upper mantle consists of the lithosphere and asthenosphere.
-The asthenosphere is semi-molten and the lithosphere is rigid.
-At the centre is the core- the densest part of the earth made of inner core and outer core- outer core liquid, inner core solid.
What are the different types of tectonic plates
Oceanic and continental
Characteristics of oceanic vs continental plates
-Location- oceanic plates make up the ocean floor, continental plates make up the earths land masses
-Thickness- oceanic (7-10km) continental (25-75km)
-Oceanic plates subduct under other plates, continental plates do not
-Oceanic plates made of basaltic rock continental plates made of granitic rock
What are the processes at constructive margins
-Volcanic eruptions at constructive plate margins are basaltic and produce low viscosity lava
-Earthquakes at constructive plate margins re low magnitude and shallow focus (less than 70km deep)
What are the processes at destructive plate margins (SUBDUCT)
-Deep sea trenches and young fold mountain ranges often form at destructive plate margins
-Volcanic activity at destructive plate margins is often violent due to the high viscosity lava
-Earthquakes at destructive plate margins are high magnitudes, deep-focus (up to 700km deep) and frequent
What are the processes at conservative plate margins (plates horizontally slip past one another)
-Conservative plate margins are characterised by the meeting of two continental landmasses resulting in the formation of a fold mountain belt.
-There is not volcanic activity at collision plate margins
-Earthquakes at collision plate margins are rare- when they do happen, they are high magnitude and shallow focus - less than 70km deep.
At which plate boundary is there no volcanic activity
Conservative
What are the characteristics of volcanic eruptions at constructive plate margins
Low viscosity lava and basaltic
What are the characteristics of volcanic eruptions at constructive plate margins
-Explosive eruptions, high viscosity lava and andesitic
Which plate subducts at destructive plate margins
Oceanic plate subducts under continental plate
