Plate Tectonics Flashcards
What is the inner core of Earth?
A solid mass of iron and nickel
How does the inner core provide Earth’s internal energy?
- High pressure
- Radioactive decay of elements such as uranium
What is the outer core of Earth?
A semi-molten mass of iron and nickel
What is the mantle?
The thickest layer of Earth composed mainly of solid rock
What is the asthenosphere?
The semi-molten upper layer of the mantle which moves through convection currents generated by heat from Earth’s core
What is the lithosphere?
The uppermost part of the mantle and the crust
What is the crust?
The outermost layer of Earth’s core which is divided into tectonic plates
What are the two types of tectonic plates?
- Continental
- Oceanic
What are the characteristics of continental plates?
- Granitic rock
- 25-75km thick
- Less dense
- Lighter
What are the characteristics of oceanic plates?
- Basaltic rock
- 7-10km thick
- Denser
- Heavier
What is the theory of continental drift?
Alfreg Wegner suggested that continents move over Earth’s surface and were once connected as a super-continent (Pangea)
What is the geological evidence for continental drift?
- Identical geology in Scotland and Eastern Canada
- Tropical coal deposits found in the UK and North America
What are convection currents?
- Hot magma rises and spreads out under plates
- As magma cools, it becomes denser and sinks
What is ridge push and slab pull?
A gravity-driven system of plate movement
What is the process of ridge push?
Magma rises at constructive plate boundaries and solidifies to create new crust material, before sliding away from the ridge
What is the process of slab pull?
Dense, oceanic plates are subducted at destructive plate boundaries, pulling the rest of the plate along with it
What is another name for ridge push?
Gravitational sliding
What is sea floor spreading?
The theory that as plates move away from each other at constructive margins, the crust must be destroyed elsewhere
How is the lithosphere divided?
- 7 large plates
- 3 smaller plates
What is paleomagnetism?
A supporting theory to sea floor spreading at mid-ocean ridges due to signals of past reversals in Earth’s magnetic field within the crust
What are the four types of plate boundary?
- Destructive subduction
- Destructive collision
- Constructive
- Conservative
What happens at a destructive subduction boundary?
A denser oceanic plate subducts beneath a continental or less dense oceanic plate (e.g. South American and Nazca plates)
What happens at a destructive collision boundary?
Two continental plates meet and no subduction occurs. Instead, the sediment crumples and forms fold mountains (e.g. Eurasian and Indian plates)
What happens at a constructive boundary?
Two plates diverge and new crust is created as magma rises and solidifies through the gap
What happens at a conservative boundary?
Two plates slide past each other at different speeds without creating or destroying crust
What is the link between convection currents and gravitational sliding?
It is believed that convection currents only play a small role in plate movement, as it is mostly driven by gravity
What landforms occur at destructive subduction boundaries?
- Island arcs
- Ocean trenches
How do island arcs form?
- Plate melts as it is subducted
- Melted material is less dense and rises to the surface as plutons of magma
- This forms explosive volcanoes at the surface
- Eruptions form volcanic islands (e.g. Mariana islands)
How do ocean trenches form?
Subduction between either two O plates or an O and a C plate (e.g. Mariana Trench)
What landform occurs at a destructive collision boundary?
Fold mountains
How do fold mountains form?
- Two C plates converge
- Neither is subducted as they are of similar density
- Sediment crumples upwards to form mountains (e.g. the Himalayas)
What landforms occur at constructive boundaries?
- Ocean ridges
- Rift valleys
How do ocean ridges form?
- Two O plates move away from each other
- Basaltic magma rises and solidifies to form a ridge
- Surtsey Island, Iceland
How do rift valleys form?
- Two C plates move away from each other
- New crust is created as andesitic magma rises
- Brittle crust can fracture and create parallel faults (e.g. East African Rift Valley)
What is an example of a conservative plate boundary?
San Andreas Fault, USA
What is a hotspot?
Areas where magma plumes rise and weaken the crust, both feeding volcanoes as well as forming volcanic island chains (e.g. Hawaii)
What is the difference between island arcs and volcanic island chains?
Island arcs occur at subduction zones whereas volcanic island chains occur at hotspots
How are volcanic island chains formed?
- Magma plume creates a hotspot
- Volcanoes can form as the crust is burnt
- Plate movement drags the head of the hotspot
- Volcanoes in the chain increase in age
