Flashcards in ✅126.96.36.199 - Plate Tectonics Deck (30)
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 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?
What is the asthenosphere?
A layer of soft, plastic like rock that carries the lithosphere
How hot is the core?
5000 degrees C
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?
Mid ocean ridges
What events and landforms occur at Destructive boundaries?
What events and landforms occur at Collision boundaries?
What events and landforms occur at Conservative boundaries?
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 Caledonian 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?
Two 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
Where are rift valleys common?
Where 3 plates meet at a junction
What happens at destructive boundaries?
Dense oceanic plate descends beneath less dense continental plate. Oceanic plate melted due to friction forming magma
What happens at collision boundaries?
Two 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 a Benioff zone?
The further the rock descends, the hotter it gets. Together with the heat from friction begins to melt the plate to magma