Plate Tectonics

Who created the first modern atlas?

Abraham Ortelius

Which meteorologist proposed the theory of continental drift?

Alfred Wegener

In what year was the theory of continental drift proposed?

1912

What evidence is there to support the theory of continental drift?

• the theory of plate tectonics

• Mesosaurus fossils

• geological columns

• plant fossils

• animal fossils

• complimentary continent shapes

plate tectonics

the process whereby heated rock is moved within the Earth in vast convection currents, which drag along the underside of the Earth’s plates, forcing them to slowly drift across the planet

What is the thickness of conintental crust?

30-70km

What is the age of continental crust?

over 1,500 million years old

What is the density of continental crust?

2.6g/cm³

What is the composition of continental crust?

mainly granite

What is the thickness of oceanic crust?

6-10km

What is the age of oceanic crust?

less than 200 million years old

What is the density of oceanic crust?

3.0g/cm³

What is the composition of oceanic crust?

mainly basalt

What was discovered by Dietz?

• an alternating North/South magnetic striping pattern

• each rock stripe is 400,000 years old

• the oldest rocks are the furthest away from the Mid-Atlantic Ridge

• the ocean crust is slowly spreading away from the boundary

• sea floor spreading

How did Harry Hess support Dietz’s theory of sea floor spreading?

• explained that the convection currents were the driving force behind sea floor spreading

• found evidence of sea floor spreading, confirmed by palaeomagnetism

palaeomagnetism

the swapping of magnetic north and south poles every 400,000 years or so

convection currents

1. Heat from the core (hot spots) warms the mantle, causing it to rise up

2. This movement within the mantle moves the plates above it

3. The mantle nearer the surface cools and creates new crust

4. The mantle moves back down towards the core

ridge push

1. At a constructive plate boundary, plates are pulling apart

2. Magma rises to the surface and forms new crust

3. This heats the surrounding rocks, which expand and rise above the surface, creating a slope

4. New crust cools and becomes denser, sliding downslope away from the late margin

5. This puts pressure on the plates, causing them to pull apart

slab pull

1. At destructive plate margins, denser crust is forced under less dense crust

2. The sinking of the plate edge pulls the rest of the plate towards the boundary

What are the 6 different layers of the Earth?

• lithosphere

• asthenosphere

• mesosphere

• outer core

• inner core

• inner-inner core

What are the characteristics of the inner core?

• consists of solid iron & nickel alloy

• 4x more dense than the crust

What is the thickness of the inner core?

1200km

What is the temperature of the inner core?

6000°C

What does the outer core consist of?

semi-liquid iron & nickel

What is the thickness of the outer core?

2250km (~2000km)

What is the temperature of the outer core?

5000°C

What are the characteristics of the mesosphere?

• consists of the lower mantle

• dense

• more rigid

What is the thickness of the mesosphere?

2600km

What is the temperature of the mesosphere?

3700°C

What are the characteristics of the asthenosphere?

• consists of the upper mantle

• consists of hotter & semi-molten rock

• more fluid

What is the thickness of the asthenosphere?

200km

What is the temperature of the asthenosphere?

1700°C

What does the lithosphere consist of?

• the crust

• the rigid upper mantle

What is the thickness of the lithosphere?

50 - 100km

What is the temperature of the lithosphere?

14 - 1500°C

What is the thickness of conintental crust?

30-70km

What is the age of continental crust?

over 1.5 billion years old

What is the density of continental crust?

2.6g/cm³

What is the composition of continental crust?

mainly granite

What is the thickness of oceanic crust?

6-10km

What is the age of oceanic crust?

less than 200 million years old

What is the density of oceanic crust?

3.0g/cm³

What is the composition of oceanic crust?

mainly basalt

What is a hot spot/magma plume?

a rising column of particularly hot magma which rises through the mantle towards the crust, eventually “burning through” and penetrating the crust

How many hot spots/magma plumes are there across the globe?

125

Where are most hot spots/magma plumes not located?

on plate boundaries

Where is there a well-known hot spot/magma plume located at a plate boundary?

Iceland

Why is there much debate & uncertainty created around the hot spot theory?

the number of modifications and elaborations necessary to make the hot spot theory apply in all cases

How does the hot spot theory work?

1. Radioactive decay in the Earth's core generates very hot temperatures

2. When the radioactive decay is concentrated, magma plumes form

3. The magma plumes rise vertically

4. Eventually, the magma plumes “burn” through the lithosphere

5. Volcanic activity on the surface is induced

Which scientist came up with the hot spot theory?

J. Tuzo Wilson

What alternative theory to the hot spot theory does scientist G. Foulger (2003) offer/propose instead?

the weaknesses that exist in tectonic plates themselves should be looked at instead

How many islands make up the Hawaiian state?

19

Which Hawaiian Island is the largest?

Hawaii/the Big Island

What do all the Hawaiian Islands have in common?

they are all volcanic in origin

What are the three types of destructive plate boundary?

• oceanic vs. continental

• oceanic vs. oceanic

• continental vs. continental

What motion occurs at destructive oceanic vs. continental plate boundaries?

• one plate is forced under another

• oceanic and continental plates move towards each other

• the denser oceanic plate subducts

• as the oceanic plate subducts, increased temperature and friction cause it to melt, creating a subduction zone

What hazards occur at destructive oceanic vs. continental plate boundaries?

• volcanoes

• earthquakes

• tsunamis

What is an example location of a destructive oceanic vs. continental plate boundary?

Nazca & South American plates

What motion occurs at destructive oceanic vs. oceanic plate boundaries?

• one plate is forced under another

• oceanic and oceanic plates move towards each other, both of the same density

• the faster moving plate is the one that subducts

• the features are the same as the continental-oceanic subduction zone

• an ocean trench marks the location where the plate is pushed down into the mantle

What hazards occur at destructive oceanic vs. oceanic plate boundaries?

• volcanoes

• earthquakes

• tsunamis

What is an example location of a destructive oceanic vs. oceanic plate boundary?

South American & Caribbean plates

What motion occurs at destructive continental vs. continental plate boundaries?

• one plate is forced under another

• two continental plates move towards each other

• as both plates are of the same density, there is no subduction

• as the plates meet, sediment and the plate edges are forced to fold upwards

What hazard occurs at destructive continental vs. continental plate boundaries?

earthquakes

What is an example location of a destructive continental vs. continental plate boundary?

Indo-Australian & Eurasian plates

What motion occurs at constructive plate boundaries?

• plates pulling apart, moving away from each other

• a gap is created between the plates

• magma (molten rock) rises from the mantle and fills the gap between the plates, forming a mid-ocean ridge

What hazards occur at constructive plate boundaries?

• volcanoes

• earthquakes

What is an example location of a constructive plate boundary?

North American & Eurasian plates

What motion occurs at conservative plate boundaries?

• two plates grind past each other

• the plates often get stuck due to friction

• friction builds up over time until the plates finally jolt past each other

What hazard occurs at conservative plate boundaries?

earthquakes

What is an example location of a conservative plate boundary?

Pacific & North American plates

continental drift

the theory suggesting that the Earth’s crust is split up into large slabs called plates that slowly move along the Earth’s surface

plate tectonics

the theory suggesting that the Earth’s crust is split up into large slabs of solid rock called tectonic plates

Gondwanaland

the ancient supercontinent of the southern hemisphere

Pangaea

the supercontinent from around 300 million years ago

Mesosaurus

an extinct freshwater reptile

Glossopteris

a seed fern

magnetic anomalies

a stripy pattern in plates because of a variation in the Earth’s magnetic field/the reversal of the Earth’s poles

Benioff zone

a zone of earthquakes close to ocean trenches

outer core

a fluid layer of the Earth composed of mostly iron and nickel

inner core

the innermost layer of the Earth that is ~2400km thick

mantle

the mostly solid layer of the Earth between the core and the crust that is about 2900km thick

asthenosphere

the zone of the Earth’s mantle between the lithosphere that is hot and fluid

lithosphere

the rigid layer of the Earth made up of the crust and the solid outermost layer of the upper mantle

Moho (Mohorovicic discontinuity)

the boundary between the crust and the mantle of the Earth

crust

the outermost shell/layer of the planet

mid-ocean ridges

seafloor mountain systems

subduction zone

where oceanic crust sinks back into the mantle

viscosity

the resistance of a fluid to change shape/the thickness of a fluid

slab pull

the force that is generated from denser oceanic plates subducting beneath less dense continental plates at subduction zones

mantle plumes

a mechanism of convection within the Earth’s mantle

How are ocean ridges formed?

1. Two oceanic plates move apart in oceanic areas

2. The space between is filled with basaltic lava, forming a ridge

Which types of crust are ocean ridges formed between?

• oceanic & oceanic

How are ocean trenches formed?

1. An oceanic plate sinks below a continental plate OR an oceanic plate sinks below an oceanic plate

2. A deep section of the ocean, a deep ocean trench, is formed

Which types of crust are ocean trenches formed between?

• oceanic & oceanic

• oceanic & continental

How are rift valleys formed?

1. Plates move apart on the surface of the Earth

2. Areas of crust drop to create parallel faults to form the valley

How are fold mountains formed?

1. Rock layers are compressed as they have been forced together

2. The rock layers crumple, buckle, and fold

Which types of crust are fold mountains formed between?

• oceanic & continental

• continental & continental

How are island arcs formed?

1. During subduction at a destructive plate boundary, the descending plate melts

2. The melted material is also lighter and more gassy than the material already in the mantle, so it rises towards the surface through the crust as plutons (blobs of magma)

3. These eventually reach the surface as explosive volcanoes

4. This may form island arcs