🌋3.1.5.2 - Plate Tectonics Flashcards
How thick is the mantle?
2900km
What are intrusive rocks?
Rocks formed by the cooling of molten Magma, that crystallises and solidifies slowly below the surface. Forms coarse grained igneous rocks. Vertical dykes and inclined sills may form within.
What are extrusive rocks?
Lava that is in contact with the air or sea. It cools, crystallises and solidifies much quicker than Magma that is still underground. Fine grained rocks with small crystals.
What events and landforms occur at Destructive boundaries?
Powerful earthquakes
Volcanoes
Fold Mountains
Ocean trenches
What is glacial deposit evidence for tectonic theory?
300 million year old deposits found in Africa, Australia, Antarctica, South America and India suggest ancient ice sheet
Where are rift valleys common?
Where 3 plates meet at a junction
What happens at destructive boundaries?
Dense oceanic plate descends beneath less dense continental plate. Oceanic plate melted due to friction forming magma
What happens at collision boundaries?
Two plates of similar densities move together, causing the material between them to buckle and rise up
Where do rift valleys form?
On constructive boundaries
How do rift valleys form?
Magma rises and plates move apart
Over a magma chamber, crack and faults appear
Blocks of crust descend into mantle, creating steep sided valleys
Central plateaus sink in the middle, forming lakes
What boundaries do ocean trenches form at?
Destructive
Crust
Earth’s outer shell, between 6-70km thick
Mantle
Molten/ semi-molten layer rock layer
Outer Core
Molten outer layer of the core, mainly iron
Inner Core
Solid centre, made of iron and nickel alloys - up to 5000°c
Asthenosphere
Layer beneath the lithosphere that’s semi-molten and the plates float on
Lithosphere
Crust and the rigid upper section of the mantle, divided into the tectonic plates
Oceanic Crust- Thickness
6-10km
Oceanic Crust- Age
> 200million
Which is denser- oceanic or continental crust?
Oceanic
Oceanic Crust- Example of rock
Basalt
Continental Crust- Thickness
30-70km
Continental Crust- Age
<1500million
Continental Crust- Example of rock
Granite
What are the 2 internal energy sources?
Primordial Heat
Radiogenic Heat
What’s primordial heat?
Heat left over from Earth’s formation
What’s radiogenic heat?
Heat produced by the decay of isotopes like Uranium 238
By far the greatest source, but slowly diminishing
Explain Alfred Wagner’s theory (1912)
Continental Drift- 300 million years ago Pangea existed
List 5 pieces of evidences supporting continental drift
Fossil Fit
Tectonic Fit
Geological Fit
Jigsaw Fit
Paleomagnetism
Fossil Fit Example
Mesosaurus found in South Africa and East America
What type of fossils are looked at? Why?
Land mammals
Don’t swim, don’t lay eggs
Tectonic Fit Example
Caledonian mountain belt found in Scotland, Canada and Greenland- form a continuous linear pattern when reassembled
Why does tectonic fit support Continental Drift?
As mountain belts have to be made under the same conditions in the same location
Geological Fit Example
Mapping South America and West Africa reveals continuous rock outcrops over 2,000 million years old
Jigsaw Fit Example
Coastlines of South America and West Africa match to a depth of 1,000m below current sea level
How can gaps and overlaps in jigsaw fit be explained?
Coastal erosion
Coastal deposition
Rises in sea level
Changes in land level
How does paleomagnetism explain Continental Drift?
. Roughly every 400 million years the Earth’s magnetism changes
. At mid ocean ridges, there are striped symmetrical patterns where the rock has moved apart due to sea floor spreading
. Shows that the plates are moving
Sea Floor Spreading
Movement of oceanic crust away from constructive plate margins at mid-ocean ridges
Slab Pull
After subduction, the cooler, heavier edge of the lithosphere sinks into the mantle under its own weight, pulling the plate with in
Ridge Push
The higher elevation at mid ocean ridges causes gravity to push the lithosphere that’s further from the ridge
Gravitational Sliding
Movement of tectonic plates as a result of gravity
Benioff Zone
Where plates melt in the mantle due to increasing heat and friction
Constructive Margin
Plates move apart
Magma rises from the asthenosphere and cools, filling the gap
Constructive Margin Features (and examples)
Shield volcanoes- Eyjafjallajokull
Earthquakes
Rift valleys- East African Rift Valley
Mid-Ocean Ridges- Mid-Atlantic Ridge
Oceanic- Oceanic Margin
2 Oceanic plates move towards eachother
Faster/ denser subducts
Melts in Benioff Zone
Less dense molten material rises
Oceanic- Oceanic Margin Features (and examples)
Ocean trenches- Mariana Trench
Island Arcs- West Indes
Earthquakes
Composite volcanoes- Montserrat
Tsunamis- Boxing Day
Oceanic- Continental Margin
Oceanic and continental move towards eachother
Denser oceanic subducts
Melts in Benioff Zone
Less dense molten material rises
Oceanic- Continental Margin Features (and examples)
Ocean Trenches- Peru-Chile Trench
Composite volcanoes- Cotopaxi
Fold mountains- Himalayas
Continental- Continental Margins
Continental plates move towards eachother
Both plates have a lower density than asthenosphere
Can’t subduct
Collide and rise upwards
Continental- Continental Margin Features (and examples)
Earthquakes
Fold Mountains- Himalayas
Conservative Margin
Plates move past eachother
Friction between plates= stress builds
Suddenly released
Conservative Margin Features (and examples)
Fault line- San Andreas
Shallow earthquakes
Hotspots
Small area with unusually high concentration of radioactive elements below the surface
(Magma Plumes)
Hotspot Feature (and example)
Shield volcanoes- Mauna Loa, Hawaii
Magma Plume
Rising column of hot rock at a plate margin or through a plate
