Plate Margins- Content Flashcards
Why are the youngest rocks found at constructive plate margins?
Because new crust is being formed as magma rises from the asthenosphere to fill the gap where the plates are moving apart, and this solidifies to form new, dense basaltic rock.
What are formed when plates move apart in oceanic areas?
Mid oceanic ridges
What are formed when plates move apart in continental areas?
Rift valleys
What are the dimensions that mid oceanic ridges can reach?
Total length 60,000km
3000km above the ocean floor
What cut across mid oceanic ridges?
Transform faults
What do transform faults at constructive margins lead to?
They lead to frictional stress building up and shallow focus earthquakes being released
How are oceanic ridges formed?
When two plates pull apart there is a weaker zone in the crust and an increase in heat near the surface. The expanded crust forms a ridge. The central part of the ridge collapses and subsides into the crust below.
How are submarine volcanoes formed?
Where the crust splits there is a lower pressure zone where more liquid lava erupts to form submarine volcanoes
How are rift valleys formed?
Rift valleys are formed when the lithosphere stretches causing it to fracture into sets of parallel faults. The land between these faults collapses into deep wide valleys separated by blocks of land called horsts.
What is an example of a Rift Valley?
The Great African Rift Valley which extends 4000km from Mozambique to Red Sea down the eastern side of a Africa.
What happens if the stretching of continental plate continues?
If the stretching of the plate continues, the thinned basalt and continental rocks will drop below sea level and lead to the formation of a new ocean.
What are the three types of destructive margin?
- Oceanic towards continental
- Oceanic towards oceanic
- Continental towards continental
What are the two types of constructive margin?
- in oceanic areas e.g. Mid Atlantic Ridge
- in continental areas e.g. Great African Rift Valley
Why is new crust formed at constructive plate margins?
The gap created by the separating plates is being filled by magma rising from the asthenosphere and this solidifies to form new basaltic rock
What are the maximum dimensions of a mid oceanic ridge?
- total length 60,000km
- rise 3000km above ocean floor
What do transform faults lead to?
Transform faults lead to frictional stress building up and it is released in shallow focus earthquakes
How are rift valleys formed?
When the lithosphere stretches and fractures into sets of parallel faults. The land between these faults collapses into deep, wide valleys which are separated by upright blocks of land called horsts
What is an example of a Rift Valley?
The Great African Rift Valley which runs 4000km down the eastern side of Africa from Mozambique to the Red Sea
What happens if the stretching of a continental plate continues?
The thinned basalt and continental rocks will eventually drop below sea level, leading to the formation of a new ocean
What are the three types of destructive margins?
- oceanic towards continental
- oceanic towards oceanic
- continental towards continental
What are formed at oceanic/continental destructive?
Deep trenches such as the Peru Chile trench which is more than 8km deep
What can happen along the edge of the continental plate at oceanic/continental margins?
Sediments can be uplifted to form fold mountains such as the Andes along the a Pacific side of South America
How do earthquakes occur at continental/oceanic destructive margins?
Further friction with the continental plate builds up and can be released causing major earthquakes
What is the Benioff zone?
The place where the oceanic plate subducting beneath the continental plate starts to be melted into magma due to a build up of heat and pressure
What happens to the magma from the melted subducting oceanic plate?
It is less dense than the surrounding asthenosphere so the molten material rises in plumes of magma. When it reaches the surface, volcanoes are formed
What are the volcanoes at oceanic/continental plate margins like?
The lava has a viscous nature so it flows less easily which means it creates composite volcanoes, which are very explosive.
What happens if at destructive plate margins the eruptions take place off shore?
If the eruptions take place offshore, it can form a line of volcanic islands known as an island arc e.g. West Indies
What is an example of oceanic/oceanic destructive?
The western side of the Pacific Ocean where the Pacific plate is being sub ducted beneath the smaller Philippine plate to form the Marianas trench
What three things occur at continental/continental destructive margins?
- Sediment is forced up into fold mountains
- The friction can trigger shallow focus earthquakes
- Material is also forced downwards to form deep mountain roots
What are examples of continental/continental destructive margins?
- where the African plate is being forced northwards into the Eurasian plate, forming the Alps
- where the Indo-Australian plate is being forced into the Eurasian plate to form the Himalayas, where there is high levels of earthquakes
What occurs at conservative plate margins?
- stress is created between the plate edges which results in shallow focus earthquakes e.g. San Francisco 1906
An example of a conservative plate margin
The San Andreas fault system
