tect 1 Flashcards
What is the plate tectonic theory? What does it explain?
- Earth has a three-layered structure
- Earth’s litosphere is broken up into huge pieces -> “tectonic plates”
- Tectonic plates always moving
- Plate movements -> landforms and phenomena
Earth’s structure
Crust, uppermost mantle, mantle, core
What does the “ tectonic plate” contain?
Crust, uppermost mantle
This is what Tectonics will be focusing on
Two categories of crusts and where they are found
- oceanic (seafloor)
- continental (continents)
Which plate, continental or oceanic is denser?
Oceanic
What does the asthenosphere contain?
Semi-solid Upper mantle
What causes the athenosphere to be semi-solid?
Heat from the core causes the rocks in the Upper mantle/athenosphere to melt
Core mantle crust temperature and thickness
Core: 4400-6000deg, 3300km
Mantle: 1000-3700deg, 2900km
Crust: Lowest, 6-70km
What are the types of plate boundaries? What causes the plate boundaries to exist?
Types of plate boundaries
Divergent
Convergent
Transform
What causes them to exist?
Convection Currents
Slab-pull force
Describe what happens at divergent, convergent and transform boundaries
Divergent -> Plates move away from one another
Convergent -> Plates move towards one another
Transform -> Plates slide past one another
MEMO
Diverge means move away, so the “plates” will move away from each other.
How does convection currents lead to Divergent plate movement?
- Heat from Earth’s core -> mantle material to decrease in density
- Mantle material rises to surface
- Rising convection currents spreads magma beneath plates, dragging them apart.
- Mantle then loses heat and sinks back towards the core
- The material gets heated up again, repeating the process.
For 4:
Mantle material cools because it is at the area beneath plates that is further from the core which is the heat source, so its cooler there and the mantle material cools down, becomes denser and sinks.
When two convection currents collide with each other, plate movement is…?
Convergent
How does slab-pull force contribute to convergent plate movement?
- When two plates converge, denser crust is pulled down by gravity
- It subducts under the less dense crust, sinking under it’s own weight, pulling down the rest of the plate with it
What is subduction? Does it happen to oceanic crust, continental crust or both?
Happens to…?
Oceanic crust only. Only denser oceanic crust can subduct
What is subduction? No need memo, just know the rough meaning
Oceanic plate colliding with another tectonic plate (can be continental e.g.) and the oceanic plate descending under the other tectonic plate
Magma VS Lava
same thing except for location
Magma -> In the volcano
Lava -> Outside of volcano
How does seafloor spreading occur?
- At O-O divergent plate boundaries, when the plates diverge, a mid-ocean ridge is formed
- Magma rises from the weakened part of the crust and fills it
- New seafloor is formed after the magma is cooled.
Weakened part of the crust is as a result of the divergence (the mid-ocean ridge), you can imagine that as the plates move away, there are weaker areas of the crust just like how if you stretch an elastic material, it is more prone to breaking.
Works the same way, except that in this case, weakened parts are prone to magma rising upwards
How is a Fold Mountain formed?
- Two plate converges, buckles and folds, forming fold mountains
Evidence of Seafloor Spreading
- Age of rocks at seabed shows a pattern
pattern
- Rocks nearest to center of mid-ocean ridge youngest
- Rocks further away are progressively older
- Shows how new oceanic crust is created at divergent boundaries
What is Magnetic Striping?
- Zebra-like pattern, normal polarity rocks alternating alongside strips of reversed polarity rocks
- symmetrical on both sides
What is normal polarity of Earth?
- Earth has geographic North, geographic South
- This does not change.
- Earth has magnetic North, magnetic South
- Magnetic North, South reversed multiple times
- When the Magnetic North Points towards the Geographic North, and the Magnetic South Points towards the Geographic South, that is Normal Polarity.
Magnetic Striping occurs as…?
- When iron-rich lava erupts, cools and solidifies, forms basaltic rocks
- it’s Magnetic materials point towards Earth’s magnetic North, recording evidence of Earth’s polarity at that point of time
Three plate movements
- Convergent
- Divergent
- Transform
1 Divergent Boundary example
North American, Eurasian Plate
1 Convergent Boundary Example
Nazca, South American Plate
