1. Chapter 3 Earth Materials and Plate Tectonics
BASIC GEOLOGY
Chapter 3 Earth Materials and Plate Tectonics

2. Chapter Overview Rocks and Minerals of the Earth’s Crust
Major Relief Features of the Earth’s Surface
Plate Tectonics
Continents of the Past
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

3. Rocks and Minerals of the Earth’s Crust The Earth’s Interior
Core: spherical central mass of the Earth composed largely of iron; consists of an outer liquid zone and an inner solid zone
Mantle: rock layer of the Earth beneath the crust and surrounding the core, composed of ultramafic igneous rock of silicate minerals
Crust: outermost solid layer of the Earth, composed largely of silicate minerals
Oceanic crust: mafic rocks
Continental crust: lower zone mafic rock, upper zone felsic
Continental crust thicker than oceanic
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

4. Rocks and Minerals of the Earth’s Crust
The Earth’s Interior
Most abundant elements in crust:
Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium
Minerals: naturally occurring inorganic crystalline chemical compounds
Rocks:
Usually composed of 2 or more minerals
Rock classes: igneous, sedimentary, metamorphic
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

5. Rocks and Minerals of the Earth’s Crust
Igneous Rocks
Igneous rock: rock formed from the cooling of magma
Intrusive Igneous rock: rock formed from magma that solidifies below the Earth’s surface
Visible mineral crystals
Extrusive igneous rock: rock formed from magma that cooled rapidly at the surface or under the ocean
Mineral crystals microscopic
Magma: mobile, high-temperature molten state of rock
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

6. Rocks and Minerals of the Earth’s Crust Igneous Rocks
Most composed of silicate minerals: contain silicon and oxygen
Felsic rock:
Felsic minerals
Light-colored
Less dense
Mafic rock:
Mafic minerals
Dark-colored
More dense
Ultramafic rock:
Heavy mafic minerals
Very dense
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

7. Rocks and Minerals of the Earth’s Crust
Sediments and Sedimentary Rocks
Sedimentary Rock: rock formed from the accumulation of sediment
Clastic—formed from rock and mineral fragments
Chemically precipitated: formed by chemical precipitation from seawater or salty inland lakes
Organic: formed from organic material
Insert figure 8.6 here
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

8. Rocks and Minerals of the Earth’s Crust
Sediments and Sedimentary Rocks
Sandstone, deposited in layers
Conglomerate
Shale
Chalk, a form of limestone
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

9. Rocks and Minerals of the Earth’s Crust
Sediments and Sedimentary Rocks
Coal, a fossil fuel, is an organic sedimentary rock
Fossil Fuels: naturally occurring hydrocarbon compounds produced from remains of organic matter enclosed in rock; examples are coal, petroleum (crude oil), and natural gas
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

10. Rocks and Minerals of the Earth’s Crust Metamorphic Rocks
Metamorphic Rock: rock altered in physical or chemical composition by heat, pressure, or other processes taking place at a substantial depth below the surface
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

11. Rocks and Minerals of the Earth’s Crust The Cycle of Rock Change
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

12. Major Relief Features of the Earth’s Surface
The Geologic Timescale
4.5 billion years of Earth’s history
Divided into Eons, Eras, Periods
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

13. Major Relief Features of the Earth’s Surface
The Lithosphere and Asthenosphere
Lithosphere: rigid outer shell of Earth, includes crust and upper mantle
Asthenosphere: plastic layer below the lithosphere
Lithospheric Plate: segment of lithosphere moving as a unit, in contact with adjacent lithospheric plates along plate boundaries
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

14. Major Relief Features of the Earth’s Surface
Relief Features of the Continents
Active mountain-making regions:
Mountains result from volcanism or tectonic activity.
Active mountain-making belts form alpine chains: narrow zones along the margins of lithospheric plates
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

15. Major Relief Features of the Earth’s Surface
Relief Features of the Continents
Continental crust includes:
Active mountain-making belts
Regions of stable, older rock
Continental shields: very old, low-lying igneous and metamorphic rocks
Mountain roots: remains of older mountain belts, long, narrow ridges
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

16. Major Relief Features of the Earth’s Surface
Relief Features of the Ocean Basins
Oceanic crust <60 million years old; continental crust >1 billion years old
Ocean basins have:
Midoceanic ridge
Axial rift
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

17. Major Relief Features of the Earth’s Surface
Relief Features of the Ocean Basins
Passive continental margins: no strong tectonic activity within 50 million years
Active continental margins: deep offshore trenches, volcanic activity
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

18. Plate Tectonics
Motion of lithospheric plates drives formation of Earth’s mountains and other surface features.
Extensional tectonic activity
Spreading boundary
Plates pulled apart
Faults created
Compressional tectonic activity
Converging boundary
Plates pushed together
Creates folds and overthrust faults
Plates move past each other
Transform boundary
Transform faults
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

19. Plate Tectonics Plate Boundaries Spreading boundary
Converging boundary
Transform boundary
Plate Tectonics: theory of tectonic activity dealing with lithospheric plates and their activity
Subduction: descent of the edge of a lithospheric plate under an adjoining plate and into the asthenosphere
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

20. Plate Tectonics Subduction Tectonics
Plates undergoing subduction are associated with active continental margins
Sediments accumulate in deep trench
Deep ocean sediments
Terrestrial sediments
Deformed, scraped off subducting plate
Wedge forms at the plate boundary
Sediments transformed into metamorphic rock
Subduction: descent of the edge of a lithospheric plate under an adjoining plate and into the asthenosphere
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

21. Orogens and Collisions
Plate Tectonics
Orogens and Collisions
Continental suture: Long, narrow zone of crustal deformation produced by a continental collision; examples: Himalayan Range, European Alps.
Continental lithospheric plates converge:
Both buoyantneither subducts
Orogeny: major episode of tectonic activity resulting in strata being deformed by folding and faulting
Nappe: overturned recumbent fold of strata, usually associated with thrust sheets in a collision orogen
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

22. The Lithospheric Plates and Their Motions
Plate Tectonics
The Global System of Lithospheric Plates
The Lithospheric Plates and Their Motions
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

23. Continental Rupture and New Ocean Basins
Plate Tectonics
Continental Rupture and New Ocean Basins
Passive continental margins are created by continental rupture and spreading
Crust uplifted and stretched
Magma rises to form new rock
Rift valley forms
Rift widens and narrow ocean is formed
Ocean basin widens
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

24. The Power Source for Plate Movements
Plate Tectonics
The Power Source for Plate Movements
Radiogenic heat: heat generated by the decay of radioactive isotopes
Heat generated by decay of isotopes of uranium, thorium, potassium
Independent of surface conditions
Heat keeps rock below crust close to melting point
Radiogenic heat power source for plate motions
Exact mechanism unknown
Possibly convection currents in mantle
Possibly gravity
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

25. Continents of the Past
Alfred Wegener proposed first full-scale scientific theory of the breakup of one supercontinent into multiple drifting continents
Pangaea: supercontinent
Intact about 300 million years ago
Outlines of continents fit across ocean
Tectonic structures match across continents
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

26. Continents of the Past
Wilson Cycle: the continents have united and broken up repeatedly through Earth’s history
Movements of the continents from 200 million years ago to present
Movements of the continents from 600 million years ago to 300 million years ago
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

27. Continents of the Past
Satellite data show rates of plate movement from about 5 to 10 cm (2-4 inches) per year
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.