Tectonics - Topic 1 Flashcards
Plate Tectonics
What are convection currents?
Convection currents are currents of heat within the hot softened mantle below the crust, generated by the heat from the Earth’s core, which drive tectonic plate movements.
What is the slab-pull force?
The slab-pull force is gravitational force that causes a denser oceanic plate to sink further into the mantle under its own weight
What is subduction?
Subduction is the process of an oceanic plate colliding and descending beneath another less dense tectonic plate
What are divergent plate boundaries?
It is where plates move away from each other
What are convergent plate boundaries?
It is where plates move towards each other
What are mid-ocean ridges?
It is a submarine mountain chain linearly located on the ocean floor at divergent plate boundaries
(where the lava comes out to form new oceanic crust)
What are transform plate boundaries?
It is where plates slide past each other
What are oceanic trenches?
It is a deep depression found in the ocean floor where one oceanic plate is subducting beneath another plate (opposite of continental-continental converging
plates whereby instead of going up they go down)
What is the oceanic crust made of, and what does it contain?
The oceanic plate contains basalt, a volcanic rock.
Basalt contains minerals that can be influenced by Earth’s magnetic field
What happens at divergent plate boundaries?
The plates move away from each other, which results in mid-ocean ridges, volcanoes including submarine volcanoes and volcanic islands, rift systems and earthquakes
What happens at convergent plate boundaries?
- Plates move towards each other
- Results in fold mountains, volcanoes including submarine
What happens are transform plate boundaries
- Plates slide past each other
- Results in faults & earthquakes
What is magnetic striping?
Magnetic striping is the zebra-like pattern where there are strips of normal polarity rocks alternating alongside strips of reversed polarity roocks on the seafloor
What happens at oceanic-oceanic convergent plate boundaries?
- two oceanic plates collide
- the denser plate subducts beneath the other plate
- this forms a deep depression knows as a oceanic trench
- as the subducting plate sinks into the mantle, the high pressure forces water out of its oceanic crust. Water lowers the melting point of the overlying mantle, causing it to melt, forming magma
- magma rises through weak areas in the crust to the Earth’s surface
- this forms a chain of volcanoes, known as a volcanic island
What happens at continental-continental convergent plate boundaries?
- two continental plates collide
- subduction does not take place because continental plates are too bouyant to subduct
- enormous pressure causes the rocks to be uplifted and buckled to form fold mountains
- friction along the convergent plate boundary also causes earthquakes to occur
- magma does not rise to the surface, hence no volcanoes are formed
What happens are oceanic-continental convergent plate boundaries?
- an oceanic plate collides with a continental plate
- the denser oceanic plate subducts beneath the continental plate
- this forms a oceanic trench in the subduction zone
- as the subducting plate sinks into the mantle the high pressure forces water out of its oceanic crust. water lowers the melting point of the overlying mantle, causin it to melt, forming magma.
- magma rises through weak areas in the crust to the earth’s surface, forming volcanoes on the continental plate (friction along the subducting oceanic plate causes earthquakes to occur)
- enormous pressure at this plate boundary causes rocks lon the continental plate to be uplifted and buckled, forming fold mountains
What happens at oceanic-oceanic divergent plate boundaries?
- Two oceanic playes move apart
- The decrease in overlying pressure causes parts of the underlying matle to melt, forming magma
- magma rises through weak areas in the crusrt to the earth’s surface, and fills gaps caused by the spreading plates
What happens at continental-continental divergent plate boundaries?
- Two continental plates move apart
- Rocks eventually fracture to form parallel faults
- The rocks between these faults collapses to form a deep rift valley with steep sides
- As the plates move apart, the decrease, in overlying pressure causes parts of the underlying matle to melt, forming magma. Magma rises through weak areas. in the crust to the Earth’s surface, forming volcanoes
- Earthquakes occur as stress and tension are released when plates move
What is the lithosphere?
The lithosphere is the crust and uppermost solid part of the mantle
How do earthquakes occur?
Earthquakes occur as stress and tension are released when plates move
How do convection currents lead to tectonic plate movement?
- Heat from the eath’s core causes the mantle material to become less dense
- Mantle material rises towards the surface
- The rising convection currrents then spread beneath the plates and drag them apart, causing divergent plate movement
- The mantle material then loses heat and sinks towards the core
- Convegrent plate movement occurs where the convection currents collide
- The materials then get heated up again, and the process repeats. This rising and sinking of the mantle forms convection currents
How does the slab-pull force contribute to tectonic plate movement?
- When two plates converge, the denser oceanic crust is pulled down by gravity as it subducts beneath the less dense crust
- The desner oceanic crust sinks deeper into the mantel under its own weight, pulling the rest of the plate with it, contrubuting to furhter convergence
What is evidence of seafloor spreading?
- When two plates move away from each other at divergent plate boundaries, seafloor spreading occurs
- Magma from deep within the earth rises through the mid-ocean ridge
- New oceanic crust is formed
What’s the Geographic North?
The direction towards the fixed point on Earth called the North Pole
What’s the Geographic South?
The direction towards the fixed point on Earth called the South Pole
What’s the Magnetic North?
Direction that a compass needles points to. This is the direction of the Earth’s magnetic North pole, where the Earth acts as a magnet itself
What’s the Magnetic South?
The South direction that a compass needles points to. This is the direction of the Earth’s magnetic South pole.
What is “normal polarity”
When the Earth’s magnetic North points towards geographic North and magnetic South points towards geographic South
What is “reverse polarity”
When the Earth’s magnetic North points towards geographic South and magnetic South points towards geographic North
What is relationship between Geographic poles & Magnetic poles?
- Earth has a geographic North and geographic South as well as a magnetic North and magnetic North
- The geographic North and geographic South do not change
- However, the magnetic North and magnetic Southh can shift, and they have reversed multiple times over geological time.
- Currently, the magnetic North points roughly towards the geographic North, and the magnetic South points roughly towards the geographic North - this is known as normal polarity
- Reverse polarity happens when the Earth’s magnetic North points roughly towards geographic North and magnetic South points roughly towards geographic South
What is magnetic striping?
- Magnetic striping is the zebra-like pattern where there are strips of normal polarity alternating alongside strips of reversed polairty rocks on the seafloor
- It is symmetrical on both sides of the mid-ocean ridge
How does magnetic striping occur as?
Magnetic striping occurs as:
* Basaltic rocks from the oceanic crust are volcanic rocks formed from iron-rich laav
* They contain magnetic materials
* When the iron-rich lava erupts, it cools and solidifies
* Its magnetic materials point towards Earth’s magnetic North, recording evidence of Earth’s polarity at that time
