Plate Tectonics: Plate Movement

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Crust: state, density, composition, thickness
Solid, Least dense, Silicon Oxygen Aluminium Potassium Sodium (SOAPS), 6-70km thick
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Mohorovijic Discontinuity
The distinction between the crust and the mantle.
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Lithosphere & what state is it
The crust and the upper mantle. Solid
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Asthenosphere & state
Partially molten upper mantle. Plates float on top.
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Mantle: density, state, temperature, thickness, composition
denser, molten, 3000-5000C, 3000km thick, Silicon oxygen magnesium iron
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Outer core state, inner core state. temperature, thickness, density, composition
Outer core=liquid, inner=solid, 5000C, 2700km thick, densest due to high pressure, iron and nickel alloys
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Continental crust: Thickness, density, age, composition, rock type
30-70km, less dense, older than 1500 million, SiAl, Mainly granite
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Oceanic crust: Thickness, density, age, composition, rock type
6-10km thick, more dense, under 200 million, SiMa, Mainly basalt
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What is Plate Tectonic Theory?
A theory that attempts to explain the formation and distribution of the Earth's major structural features, in terms of a series of plates that make up its crust.
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How do plates move?
Via convectional currents in the Earth's aesthenosphere moving the lithosphere above.
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Who first theorised continental drift and when?
Alfred Wegener in 1912
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Name of the original supercontinent?
Pangea
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4 pieces of evidence for continental drift
Biological, geological, climatological, 'jigsaw-fit'
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Example of Jigsaw fit
West coast of africa and east coast of south america
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Why was jigsaw fit not totally accepted originally?
They don't fit exactly. It was only until the discovery of continental shelves later in the century that continental fit was regarded as a legitimate theory.
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Who first observed continental fit and when?
Sir Francis Bacon in 1620
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Example of Geological evidence for continental drift
Broad belts of rock in South Africa and Argentina of the same age and structure that align when joining the continentss
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Example of Biological evidence for continental drift
The discovery of the fossils of Mesosaurus and Glossopteris on both sides of the Atlantic meaning that Europe and America were once joined.
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Example of Climatological evidence for continental drift
Antarctica and the UK have oil and coal deposits of a similar age and so much have been in tropical climate zones at some point since the carboniferous period.
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Who discovered the Mid-Atlantic Ridge and when?
Maurice Ewing in 1948
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How long is the Mid-Atlantic Ridge?
40,000km
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What did the discovery of the Mid-Atlantic Ridge lead to?
The development of Paleomagnetic theory
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What is Paleomagnetism?
Study of bands of rock created parallel to mid-ocean ridges that have alternating directions of iron particle alignment. This helps us chart the fact that approximately every 400,000 years the Earth's polarity reverses.
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How often does the Earth's polarity reverse?
Approx. every 400,000 years
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Who discovered Sea floor spreading?
Harry Hess at Princeton University in the 1960's
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What is Sea floor spreading?
A process which occurs at mid-ocean ridges, where oceanic plates diverge, causing tensional stress and fractures in the lithosphere. Basaltic lava then rises up the fractures and cools on the ocean floor to create new crust.
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What is a new theory of the mechanism of plate movement that is being explored as potentially accurate than convection current theory?
Slab Pull Ridge Push theory
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What happens at Destructive plate boundaries, and what is another name for them?
Here plates collide, also known as a convergent boundary
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Example of an oceanic-continental destructive margin and the features it creates?
Nazca and South American plates. makes the Peru-Chile trench and the Andes fold mountains.
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What is the Benioff Zone?
The point where, at destructive boundaries, the friction and pressure becomes so great that the subducted plate melts.
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What percentage of volcanoes are above subduction zones?
90%
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What type of volcanoes/eruptions are found at destructive margins?
Composite cones/Acid lava domes, explosive & violent with long dormant periods.
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Example of an oceanic-oceanic destructive margin and the features it creates?
The Pacific plate subducting under the smaller Philippine plate. Creates the Marianas trench and an island arc called the Mariana Islands, including Guam.
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Example of a continental-continental destructive margin and the feature it creates?
Indian and Eurasian plates, Due to lower density of contiental plates in comparison to the lithosphere, there is little subduction. creates the Himalayas.
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What happens at Constructive plate boundaries, and what is another name for them?
Where plates move apart. Also known as Divergent plate boundaries.
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Example of a continental-continental Constructive margin and the feature it creates?
The Great African Rift Valley at the Afar Triple Junction which is splitting the African Plate.
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Example of an oceanic-oceanic Constructive margin and the feature it creates?
North American & Eurasian boundary, creating the Mid-Atlantic Ridge
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What happens at a Constructive margin in detail?
The plates are pushed apart by convection currents in the Aesthenosphere and the rising magma which fills the space between the diverging plates. The basaltic lava cools and forms new crust.
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What happens at a Destructive margin in detail?
The denser/older plate is subducted under the other plate because it is heavier. The friction casued by the plates pushing agaisnt each other causes the subducted plate to heat up, melting to form magma at the Benioff zone.
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What type of volcanoes/eruptions are found at Constructive margins?
Lava Plateaus/Shield volcanoes. Regular, gentle, continuous.
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What happens at Conservative plate boundaries, and what is another name for them?
Where plates move alongside each other, either in opposite directions or at different speeds. Also known as Transform plate boundaries.
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What type of volcanoes/eruptions are found at Conservative margins?
No crust is created or destroyed, so there are no volcanoes created, although shallow focus earthquakes occur.
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Example of a Conservative boundary and the feature it creates?
The North American plate moving slower than the Pacific plate. Creates the San Andreas fault in California.
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What landforms are found at destructive margins?
Fold Mountains, Deep sea trenches, Island arcs
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What is a deep sea trench and how are they formed?
A narrow, elongate, v-shaped depression in the ocean floor. They are created as oceanic plates subduct under another plate, either continental or oceanic, creating a deep trench in the ocean floor.
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Pressure at a deep sea trench can be up to ___________ per_______
16,000 pounds per square inch
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How deep is the deepest part of the ocean?
The Marianas trench extends to 10.9 km deep.
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What is an island arc and how are they formed?
A curved chain of volcanic islands located at a destructive margin, typically with a deep ocean trench of the convex side. Created by an upwelling of magma formed from crust of a subducted plate melting at the benioff zone, making volcanic islands.
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What landforms are found at constructive margins?
mid-ocean ridges and rift valleys
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What is a mid-ocean ridge and how are they formed?
A elongated raise in the ocean floor, consisting of thousands of individual volcanoes or volcanic ridge sediments which periodically erupt. Each eruption adds a thin coat of lava. This process is ongoing and perpetual.
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How thick is the layer of lava added to a mid-ocean ridge each eruption?
Less than 10 metres thicks
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At the Juan de Fuca ridge, the spreading process creates an average of __ width of new crust every ____.
At the Juan de Fuca ridge, the spreading process creates an average of 6 metres width of new crust every 100 years.
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What is Surtsey and why is it important?
Surtsey is an island off of Iceland that is made form a volcano in from the Mid-Atlantic ridge. It breached the surface of the ocean in the 1960's. Helps scientists to track the creation of volcanic islands.
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What is a rift valley and how are they formed?
A lowland region that forms where Earth's tectonic plates move apart. They consist of raised arches of crust in which large linear blocks have subsided.
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Where is the Great African Rift Valley and how long is it. What is its extension rate?
It extends 6000km from Ethiopia to Mozambique, with an extension rate of 0.5cm per year.
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Name 2 volcanoes found in the Great African Rift Valley
Mount Kilimanjaro and Mount Kenya
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What are Hot Spots?
Volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle
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How are they formed?
It is thought that the Earth's mantle is heated by radioactive decay. Whilst it is not known for certain, it is largely agreed that a concentration of certain elemnts wihtin the mantle creates a section of superheated molten rock called a hotspot.
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What type of volcano is formed from a hotspot?
An active basaltic shield volcano.
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Name an example of a volcanic island created form a hotspot, the island chain that it belongs to, and when it was last active.
Maui, part of the Emperor seamount chian, last active 1.1 million years ago/
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What happens if a plate moves quickly over a hotspot compared to if it moves slowly?
If the plate moves quickly, a line of islands will be created (Hawaiian Islands). If the plate moves slowly, a cluster is formed (Canary Islands)
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What happens when an extinct volcanic island gets eroded?
First they become seamounts, and then once eroded to below sea level they becomes guyots.
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Do hot spots move and where are they found?
They remain stationary and can be found anywhere, near or far from plate boundaries.
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How many hot spots have been active during the last 10 million years?
100
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How many major hot spots are currently active?
25
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Roughly __% of all earthquakes occur along _______
Roughly 90% of all earthquakes occur along the Ring of Fire
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The Ring of Fire is home to __% of all active volcanoes on Earth.
The Ring of Fire is home to 75% of all active volcanoes on Earth.
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Why are the tectonic boundaries of the Ring of Fire so active? Give an example.
They are mostly subduction zones; for example the Nazca and Cocos Plates being subducted under the westward-moving South American Plate.
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What is induced seismicity?
Induced seismicity refers to typically minor tremors and earthquakes that are caused by human activity altering the stresses and strains on the Earth's crust.
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Give and example of induced seismicity.
In 1967, a 6.3 earthquake occurred in Maharashtra, India, located near or directly under the Koyna Dam Reservoir.
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Why are dams thought to be responsible for earthquakes?
Dams with heights higher than 100 metres seem to experience increased seismicity. The extra water pressure created by large reservoirs is the most accepted explanation.
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Other cards in this set

Card 2

Front

Mohorovijic Discontinuity

Back

The distinction between the crust and the mantle.

Card 3

Front

Lithosphere & what state is it

Back

Preview of the front of card 3

Card 4

Front

Asthenosphere & state

Back

Preview of the front of card 4

Card 5

Front

Mantle: density, state, temperature, thickness, composition

Back

Preview of the front of card 5
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