Plate Tectonics Flashcards
Describe the crust:
The thin layer of the outer shell that we live on, 5-10km thick beneath oceans and 70km thick beneath continents, lithosphere
Describe oceanic plates:
An occasionally broken up layer of basaltic rocks known as sima - silicon and magnesium
Describe continental plates:
Bodies of mainly granite rocks, known as sial - silicon and aluminium
What is the lithosphere?
The crust and upper mantle, where tectonic plates are formed
How thick is the mantle?
2900km
What is the asthenosphere?
A layer of soft, plastic like rock that carries the lithosphere
How hot is the core?
5000 degrees Celsius
What are intrusive rocks?
Rocks formed by the cooling of molten Magma, that crystallises and solidifies slowly below the surface. Forms coarse grained igneous rocks. Vertical dykes and inclined sills may form within
What are extrusive rocks?
Lava that is in contact with the air or sea. It cools, crystallises and solidifies much quicker than Magma that is still underground. Fine grained rocks with small crystals
What is gravitational sliding?
The movement of tectonic plates under the influence of gravity
What is ridge push?
Gravity acting on the weight of the lithosphere near the ridge pushes the older part of the plate in front
What is slab pull?
The lithosphere sinks into the mantle under its own weight following subduction, helping to ‘pull’ the rest of the plate with it.
What events and landforms occur at Constructive boundaries? (3)
Volcanoes
Mid ocean ridges
Rift Valleys
What events and landforms occur at Destructive boundaries? (4)
Powerful earthquakes
Volcanoes
Fold Mountains
Ocean trenches
What events and landforms occur at Collision boundaries? (2)
Powerful earthquakes
Fold Mountains
What events and landforms occur at Conservative boundaries?
Powerful earthquakes
What is jigsaw fit evidence for tectonic theory?
Similarity in outlines of West Africa and South America as well as other continental areas. best fit at 1000m below sea level
What is geological fit evidence for tectonic theory?
Ancient rock outcrops from South America and West Africa from over 2000 million years ago were continuous
What is Tectonic fit evidence for tectonic theory?
Fragments of the Caldeonian mountain belt are found in Scotland, England, Greenland, Canada and Scandinavia
What is glacial deposit evidence for tectonic theory?
300 million year old deposits found in Africa, Australia, Antarctica, South America and India suggest ancient ice sheet
What is fossil evidence for tectonic theory?
Bands of identical fossils lie across continents, particularly of organisms which could not have travelled
What happens at a conservative boundary?
2 plates do not directly collide but slide past one another
What happens at a constructive boundary?
2 plates are moving apart, leaving a gap for magma to rise up through. Volcanoes form but don’t erupt with force and earthquakes occur
What are rift valleys common?
Where 3 plates meet at a junction
What happens at destructive boundaries?
Dense oceanic plate descends beneath dense continental plate. Oceanic plate melted due to friction forming magma
What happens at collision boundaries?
2 plates of similar densities move together, causing the material between them to buckle and rise up
Where do rift valleys form?
On constructive boundaries
How do rift valleys form?
- Magma rises and plates move apart
- Over a magma chamber, crack and faults appear
- Blocks of crust descend into mantle, creating steep sided valleys
- Central plateaus sink in the middle, forming lakes
What is the Benioff zone?
The further the rock descends, the hotter it gets. Together with the heat from friction begins to melt the plate to magma
What boundaries do ocean trenches form at?
Destructive
What is a convection current?
Convection currents, that occur within the molten rock in the mantle, act like a conveyor belt for the plates. Tectonic plates move in different directions. The direction of movement and type of plate margin is determined by which way the convection currents are flowing.
What is seafloor spreading?
a geologic process in which tectonic plates—large slabs of Earth’s lithosphere—split apart from each other. Seafloor spreading and other tectonic activity processes are the result of mantle convection.
How do fold mountains form?
where two or more of Earth’s tectonic plates are pushed together. At these colliding, compressing boundaries, rocks and debris are warped and folded into rocky outcrops, hills, mountains, and entire mountain ranges. Fold mountains are created through a process called orogeny.
How do ocean ridges form?
Mid-ocean ridges occur along divergent plate boundaries, where new ocean floor is created as the Earth’s tectonic plates spread apart. As the plates separate, molten rock rises to the seafloor, producing enormous volcanic eruptions of basalt.
How do ocean trenches form?
feature of convergent plate boundaries, where two or more tectonic plates meet.
dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench.
How do island arcs form?
Where two oceanic plates converge the denser crust subducts the other. This creates a trench. As the oceanic plate descends it melts, and the magma rises forming a volcanic island chain, known as an island arc.