Theory of Plate Tectonics Flashcards
Who came up with the theory of continental drift?
Alfred Wegener
What is the lithosphere?
the solid rock making up the crust and upper part of the mantle
How do fossils provide evidence of continental drift?
- fossils of species found on different, separate continents
- not able to travel by air/sea
- continents previously must have been closer
- e.g mesosaurus
How does jigsaw fit provide evidence for continental drift?
- continents look as if they fit together
- suggests at one point they were joined
Explain how paleo-magnetism shows sea-floor spreading
- iron-rich minerals in lava, rise through crust
- these align with magnetic field at the time
- lava cools and sets in this alignment
- polarity is able to be recorded, changes every 400,000 years
- symmetry in the bands of lava suggest sea floor is spreading
What are 3 things that cause plate movement?
- convection currents
- ridge push
- slab pull
Briefly outline how convection currents move plates
- radiogenic heat causes magma to become hot and less dense. It rises
- when near the lithosphere, it cools and becomes more dense. It sinks
- circular currents in asthenosphere drive movement in lithosphere.
Briefly outline how ridge push causes plate movement
- hot magma rises and heats surrounding rock
- asthenosphere and lithosphere expand and become elevated
- causes a slope
- rock cools and becomes more dense
- gravity causes older, denser lithosphere to slide away
- exerts force on plates
What 2 types of heat are in the Earth’s core?
- radiogenic and primordial
What is the asthenosphere?
the semi-molten layer below the lithosphere, upon which the plates float
How does geology provide evidence for continental drift?
Rocks of the same age and type are found where countries would have fitted together
Briefly outline how slab pull causes plate movement
- one plate is denser and heavier than the other plate
- subducts beneath less dense plate
- sinking edge exerts a force which continues to pull the subducting plate underneath
What is the Benioff zone?
where the lithosphere is passing into the asthenosphere, with friction and heat causing melting of the oceanic plate
On what type of plate boundary is the San Andreas Fault found?
Conservative
What process(es) form a deep-sea trench?
subduction and downwarping
Where are rift valleys found?
continental-continental divergence
What is the definition of a magma plume/hot spot?
Areas of high heat flow within the mantle.
How do convection currents cause hotspots?
- Convection currents draw heat directly towards a section of the lithosphere
- This section of the crust receives continued and concentrated heat
What is meant by the term ‘accretion wedge’?
the build up of material at the point of subduction
Theory 1 of hotspots
concentrated heat on a specific area of the lithosphere
causes volcanic activity on surface
plates move whilst hot spots remain stationary
What is a concentrated stream of magma called?
magma plume
Theory 2 of hotspots
Weaknesses in the plate caused by past plate movement allows magma to rise through fissures in the crust
Example of theory 1
Hawaii - Mauna Loa
kilauea
example of theory 2
Iceland
What 2 plates are involved in the Great African Rift Valley?
African and Nubian
Where are island arcs formed?
oceanic oceanic destructive
