1. Topic 1- Tectonic Impacts
This is the first topic of the Earth and Environmental Science HSC Course. It’s very similar to the last topic you studied: Dynamic Earth however you will look at the tectonic theory in more detail.

2. Topic Overview There are 6 parts to this Topic: Lithospheric Plates
Volcanic Mountains
Tectonic Mountains
Evolution of Continents
Earthquakes, Volcanoes and Natural Hazards
Climate Change

3. Topic Outcomes Describe the lithospheric plates and their motion
Explain how the movement of plates results in mountain building
Explain how continents grow and change shape as plate boundaries move and change
Describe how natural disasters are often associated with tectonic activity like earthquakes and volcanoes
Explain how environmental conditions caused by tectonic activity may contribute to the problems experienced by people
Explain the link between plate tectonics and climate, both in the short term and throughout geological history.

4. Part 1-Lithospheric Plates Lesson 1
In this part you will be studying lithospheric plates in great detail. We will be reviewing a lot of content covered in the last Topic.

5. Introduction
In the last topic you studied: Dynamic Earth, you studied plate tectonics and the forces which drive them. These plates are the top part of the lithosphere.

6. The Lithosphere
The lithosphere is the rigid, brittle outer layer of the Earth. Lithos means rocks. Above the lithosphere is the hydrosphere and atmosphere.

7. Asthenosphere
This is the section below the lithosphere and consists of the upper part of the Mantle. Astheno means weak or without strength. It’s made up of partially molten rock which scientists call it’s state to be “plastic”.

8. Mesosphere
Everything below the asthenosphere: the rest of the mantle, outer and inner core is called the mesosphere. Meso means middle.

9. Earth’s Interior
How do scientists know so much about Earth’s interior? After all humans have never even breached the crust….. Seismologists provide us with the information.

10. Earth’s Interior
Seismologists are scientists who study earthquakes. When an earthquake happens an extreme amount of energy is released. This energy travels in waves (seismic waves) through the Earth. By studying the behaviour of these seismic waves scientists are able to estimate the thickness and composition of the Earth’s interior.

11. Earth’s Interior
As the seismic waves pass through layers of the Earth, the energy changes speed and direction. This is due to the materials having different densities.

12. Earth’s Interior
Understanding the Earth’s interior is vital to our understanding of crustal plates and their movements. So why do we care?

13. Earth’s Interior
We care because this information can save lives and property by helping to predict earthquakes and volcanoes. It also helps us to explain the current distribution of plants and animals and predict future outcomes.

14. Lesson-2
Crustal Plate Review

15. The Theory of Plate Tectonics
If we look at a globe carefully, most of the continents seem to fit together like a puzzle. The West African coastline seems to fit nicely into the east coast of South America. The fit is even more striking when the submerged continental shelves are compared rather than the coastlines.

16. The Theory of Continental Drift
Alfred Wegener ( ) noticed the same thing and proposed that the continents were once compressed into a singe protocontinent which he called Pangea (meaning ‘All lands’) and over time they have drifted apart.

17. The Theory of Continental Drift
Wegener’s Hypothesis lacked a geological mechanism to explain how the continents could drift across the Earth’s surface as he had proposed. In 1929 Arthur Holmes elaborated one of Wegener’s many hypothesis:

18. The Theory of Continental Drift
Arthur Holmes stated that the mantle undergoes thermal convection. And that this thermal convection was like a conveyor belt and that the upwelling pressure could break apart a continent and then force the broken continent in opposite directions carried by the convection currents.

19. The Theory of Continental Drift
Not until the 1960’s did Holmes’ idea receive any attention. Greater understanding of the ocean floor and the discoveries of features like mid-ocean ridges, geomagnetic anomalies parallel to the mid-ocean ridges, and the association of island arcs and oceanic trenches occurring together and near continental margins, suggested convection might indeed be at work.

20. The Theory of Continental Drift
To understand this theory better we need to look at the geological processes taking place and the evidence which supports it. We’ll start by looking at the crust.

21. Earth’s Crust
The crust covers the mantle and is the Earth’s hard outer shell, the surface we are living on . Compared to the other layers the crust is much thinner.

22. Earth’s Crust
The crust is made up of solid material but this material is not the same everywhere. There is an oceanic crust and a continental crust.

23. Oceanic Crust
This crust is below the ocean and is 6-11 km thick. The rocks of the oceanic crust are very young compared with rocks of the continental crust; not older than 200 million years. The main rock type is basalt and the average density is 3g/cm^3

24. Continental Crust
Continental crust is the part of Earth’s crust not covered by water. This is much thicker than oceanic crust with an average of about 30-40km and a maximum of 70km. Continental crust is much older, some rocks are 4.1 billion years old. Continental crust consists of igneous rocks such as Granite. The average density is 2.7g/cm^3

25. Plate Boundaries
The Theory of Plate Tectonics builds on Wegener’s Theory of Continental Drift. This theory states that the Earth’s crust or Lithosphere is broken up into “tectonic plates”

26. Plate Boundaries
If we analyse the distribution of earthquakes around the world, we are able to identify the locations of the plate boundaries. Why would we associate earthquakes with plate boundaries?

27. Plate Boundaries
If we imagine the tectonic plates like blocks of wood, there are three ways they can interact.

28. Plate Boundaries
Remember what Holmes said about convection currents? He stated that the mantle undergoes thermal convection. And that this thermal convection was like a conveyor belt and that the upwelling pressure could break apart a continent and then force the broken continent in opposite directions carried by the convection currents. What type of plate boundary would assimilate with Holmes’ idea?

29. Divergent Plate Boundary
Divergent plate boundaries are located where plates are moving away from one another. This occurs above rising convection currents as Holmes suggested. Mid-ocean ridges are found at this boundary.

30. Convergent Plate Boundary
Convergent plate boundaries are locations where plates are moving towards one another. The plate collisions that occur in these areas can produce earthquakes, volcanoes and crustal deformation. Subduction zones are found at this boundary. There are three different types of convergent boundaries which we will discuss more later.

31. Transform Plate Boundary
Transform plate boundaries are locations where two plates slide past one another. The fracture zone that forms a transform plate boundary is known as a transform fault. Most transform faults are found in the ocean basin and connect offsets in the mid-ocean ridges.

32. Tectonic Impacts Vocab List
Homework
Complete DOT Point 1.1, 1.3
Read pages 1-5 HCS Spotlight Text
Start electronic vocab list of all bold terms pg1-5 Spotlight Text
Eg:
Tectonic Impacts Vocab List
Plate: Large pieces of the Earth’s crust

33. Lesson-3
Plate Interactions

34. Divergent Plate Boundary
This is where two plates separate. These spreading zones are where new crust is being generated. Mid-ocean ridges mark divergent plate boundaries.

35. Divergent Plate Boundary
These boundaries are some of the most active on Earth. Volcanoes at these boundaries produce basalts low in silica. This means the lava has a low viscosity and releases gasses easy. Eruptions are therefore less explosive.

36. Divergent Plate Boundary
Lava usually erupts in long cracks in the Earth’s surface called fissures rather than mountains. This is because the crust is being pulled apart rather than forced together.

37. Divergent Plate Boundary
Rocks at divergent boundaries do not usually undergo metamorphism. Earthquakes are shallow as the forces cause rocks to crack and sink along fault lines.

38. Divergent Plate Boundary
General Composition of Igneous Rocks:
Oceanic Divergence
Basaltic
Low silica content
High concentration of dark coloured mafic minerals
Continental Divergence
Rhyolitic
Rich in silica and felsic minerals
Light in colour

39. Convergent Plate Boundary
This is where two plates come together ‘collide’. There are three types of convergent zones:
oceanic-oceanic
oceanic-continental
Continental-continental

40. Oceanic-Oceanic Convergence
This type of boundary occurs between two pieces of oceanic crust. Because no buoyant continental crust is involved we do not get large mountain ranges.

41. Oceanic-Oceanic Convergence
As one plate is forced beneath the other, it is melted and a line of volcanoes form in the same way as described in a oceanic- continental convergent boundary.

42. Oceanic-Oceanic Convergence
The volcanoes that are created at this boundary form a curved line out of the sea and scientists call these island arcs.

43. Oceanic-Oceanic Convergence
Examples of island arcs include the Philippine Islands, Japan and Indonesian Islands.

44. Oceanic-Oceanic Convergence
Metamorphism occurs at these boundaries and the trenches formed are the deepest on the planet. The Mariana Trench is 11 kilometres deep. These boundaries also have deep and shallow earthquakes.

45. Ocean-ocean Convergence Plate Boundary
General Composition of Igneous Rocks:
Mainly Basalts
Increase in Andesites as island arcs mature
High silica granite and less silica gabbro intrusions can be found within the crust

46. Oceanic-Continental Convergence
Because oceanic crust is more dense than continental crust, when these two types of crust collide the oceanic crust is always forced into the mantle (subducted).

47. Oceanic-Continental Convergence
Where the oceanic crust is bent downward, trenches form. These are the deepest parts of the ocean and are used to help indicate the edge of a plate.

48. Oceanic-Continental Convergence
As the subducting oceanic plate is forced beneath the overriding continental plate, the continental plate is lifted and folded upwards producing mountains.

49. Oceanic-Continental Convergence
An example of a oceanic- continental convergent plate boundary is along the west coast of South America. Here we find the Andes Mountains.

50. Oceanic-Continental Convergence
The Oceanic Nazac plate is slamming into the Continental South American plate

51. Oceanic-Continental Convergence
If we visit this plate boundary we can see the evidence which supports this theory.

52. Oceanic-Continental Convergence
Something else happens at this boundary which produces mountains. As the oceanic crust is forced deeper into the Earth, intense heat and pressure cause it to melt. And what happens to materials when we heat them?

53. Oceanic-Continental Convergence
They rise! The oceanic plate turns into magma and rises into the overlying continental crust. This is called a magma plume. If this plume reaches the surface we get volcanoes!

54. Oceanic-Continental Convergence
A key feature to this magma is that it is rich in silica which comes from the sediments in the oceanic crust or the melted part of the continental crust.

55. Oceanic-Continental Convergence
This high silica magma makes it more viscous (thicker) which allows it to trap gasses within it. Volcanic eruptions at such boundaries tend to be very explosive because of the intense heat and pressure build up.

56. Oceanic-Continental Convergence
This type of silica rich and explosive eruption is called andesitic volcanism (after the Andes Mountains).

57. Oceanic-Continental Convergence
But what happens if the magma never makes it to the surface? That’s a great question! The magma that has collected within the continental crust can slowly cool to form granite or similar intrusive igneous rocks.

58. Oceanic-Continental Convergence
Eventually the surrounding material is eroded away and we can see these frozen granite plumes today on the surface of the earth.

59. Oceanic-Continental Convergence
Stone Mountain in Georgia (USA) is an example of just how big these frozen granite magma plumes can get.

60. Oceanic-Continental Convergence
So what happens to the rocks on the continental crust that come into contact with these magma plumes?

61. Oceanic-Continental Convergence
They are changed ‘metamorphosed’ into a different rock. This is how we get metamorphic rocks.

62. Oceanic-Continental Convergence
When these rocks are uncovered due to weathering and erosion, we can see where this contact metamorphism has happened.

63. Oceanic-Continental Convergence
Oceanic-continental convergence boundaries also experience a lot of seismic activity. Earthquakes are quite common as the two plates are crushing into each other.

64. Oceanic-Continental Convergence
An earthquake’s focus is the exact point where the rocks in the crust break or move. At a subduction zone, scientist can measure both deep and shallow earthquakes. This provides further evidence that the oceanic plate is being forced into the mantle.

65. Ocean-continental Convergence Plate Boundary
General Composition of Igneous Rocks:
Andesites are most common
Rhyolites and basalts can be found
High silica content
Intrusions of high silica granite and low silica gabbro can be found within the crust

66. Continental-Continental Convergence
This type of boundary is where two continental pieces of crust slam into each other. This boundary is different than the last because there is not complete subduction.

67. Continental-Continental Convergence
This is because the continental crust is so buoyant. Instead the plates become intensely folded and uplifted. An example of this is the Himalayas.

68. Continental-Continental Convergence
Earthquake foci are shallow at this boundary and there is no contact metamorphism. Instead there is regional metamorphism. Low heat, high pressure.

69. Continent-continent Convergence Plate Boundary
General Composition of Igneous Rocks:
No volcanic rocks
Granite intrusions common (high silica content)
Remnants of oceanic crust (basalts) found here

70. Homework
Complete DOT Point 1.2

71. Forces that drive plate movement
Lesson 4
Forces that drive plate movement

72. Two Theories
There are two hypothesis to explain the driving force behind plate tectonics.
Plates are carried and moved on top of the mantle by convection currents within this plastic molten material.
Plates are carried and moved by a combination of forces; ridge-push and slab-pull acting under the force of gravity.
Video

73. Convection Currents
Convection currents within the mantle generated by radioactive decay in the core, cause molten material to rise towards the crust.

74. Convection Currents
As this molten material reaches the crust it cools and moves horizontally dragging the crust with it.

75. Convection Currents
As the molten material drags the lithosphere horizontally and cools, it begins to sink back into the mantle. The lithospheric plate is carried with it.

76. Convection Currents
The plate is recycled into the molten mantle and the convection cycle starts again.

77. Homework
Complete DOT Point