GENERAL TECTONICS Flashcards
What is meant by the term crust?
The crust is the outmost layer of the earth.
What is meant by there term plate?
A plate is piece of the earths crust.
What is meant by the term plate margin?
A plate margin is where two plate meet.
What is meant by the term mantle?
The mantle is the layer of the earth that is below the crust and it is made up of semi molten rock.
Describe what is happening at a conservative plate margin.
The two plates are moving vertically past each other in the same direction.
The San Andreas fault is an example of what type of plate margin?
It is an example of a conservative plate margin.
Describe three difference between oceanic and continental crust.
Oceanic crust is denser, thinner and younger than continental crust.
What is meant by the term subduction.
It is where an oceanic crust dives downwards into the mantle because it has meet another plate.
Describe why the island of Iceland is becoming wider?
Because it is formed on a constructive plate margin. As the plates move apart vertical weaknesses in the crust are formed. Magma then rises along these weaknesses to form new land.
Explain why are the plates at a constructive plate margin moving apart?
This is because the margin is above a rising convection current that diverges when it hits the bottom of the crust. This pulls the two plates apart.
Define the term collision plate margin.
It is where two continental plates moving in different direction meet.
What geographical features are formed at collision plate margins.
The feature that is formed are young fold mountains such as the Himalayas.
What type of plate margin runs along the west coast of South America.
A destructive plate margin.
What type of plate margin runs north to south down the centre of the Atlantic Ocean.
A constructive plate margin.
Explain why convection currents develop in the mantle.
They develop because of localised radio active decay in the upper core. This process produce heat which warms the rock of the overlying mantle.
Explain why oceanic crust subducts under continental crust.
It subducts because it is denser than the continental crust.
Briefly explain why fold mountains are formed.
They are formed because continental crust is of the same density. Therefore when two continental plates collide one can not subduct underneath the other.
Explain why the crust of a subducting plate melts when in drops into the mantle.
It melts because the pressure increases as the crust drops into the mantle.
What type of crust is 25 to 100 km thick and mostly made of granite.
Continental crust.
What type of crust is 5 to 10 km thick and mostly made of basalt rocks.
Oceanic crust.
At what type of plate margin is crust destroyed.
At a destructive margin.
What type of volcanoes are mainly found on constructive plate margins.
Shield volcanoes.
How fast in millimetres is the Mid Atlantic Ridge moving apart.
It is moving apart at between 20 to 40 mm a year.
