Plate Movements Flashcards
What is the Theory of Plate Tectonics?
The theory that the earth’s lithosphere comprises a number of large tectonic plates which have been slowly moving since 3-4 billion years ago. Idea relies on the concept of continental drift.
What is sea-floor spreading?
Sea floor spreading is the usual process at work at divergent boundaries, leading to the creation of new ocean floor. Samples collected show how the age of oceanic crust increases with distance from the spreading centre.
Key Developments supporting the theory of plate tectonics
-JIGSAW COASTLINES(e.g A and SA)
-MID-ATLANTIC RIDGE (seafloor spreading)
-EARTH’S INTERNAL STRUCTURE - Core produces radioactive decay - mantle moves and all areas have different properties and temperatures.
-MATCHING ROCK TYPES, GEOLOGICAL STRUCTURES AND FOSSILS
-MANTLE CONVECTION = causes plates to move due to the movement of magma by convection currents.
-SEISMOGRAPH STATIONS - Wadati Benioff Zones. Allows us to see where earthquakes will happen. Mirrors subduction zone at plate boundaries.
- PALAEOMAGNETISM- results from the zone of magma ‘locking in’ the Earth’s magnetic polarity when it cools. Scientists can use this to determine historic periods of large scale tectonic activity through the reconstruction of relative plate margins. They can create a sea-timeline.
Mantle Convection
1)Convection currents cause magma to rise causing an ocean ridge.
2)Ridge Push- After being pushed upwards the plates are then forced back downhill due to gravity.
3)Slab Pull- The plate is forced back into the mantle due to gravity. Above and ocean trench is formed.
4)Trench suction- Occurs as a plate gets pushed back into the mantle due to small convection currents.
What is a Wadati Benioff Zone?
An area of deep and intermediate earthquakes.
They occur along a subduction zone as the oceanic plate is being pulled into the mantle.
The Subduction of the oceanic plate proves that trench subduction is real.
How do plates move?
Convection currents cause plates to move as the convection cells make contact with the base of the crust, causing friction, and it drags the crust along in the direction of convection.
Different types of boundaries cause different processes due to different densities of plates.
Alfred Wegner and Pangea
Hypothesised that land masses formed a single supercontinent called Pangea and this was supported by fossils and different rock types.
How does the Earth’s magnetic field contribute to the understanding of plate tectonics?
It reverses periodically which changes the direction of magnetic field. Rocks when cooled reveal which way the magnetic field was.
What happens along a subduction zone?
Along a subduction zone, one plate is forced beneath the other, causing geological activity such as the formation of ocean trenches and volcanic arcs. This process and cause earthquakes and can recycle materials, contributing to mountain formation and and altering the surrounding crust.
Examples of each plate boundary
Transform/conservative= San Andreas Fault
Convergent/destructive= Pacific Ring of Fire.
Divergent/constructive= Galapagos Rise
