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• The lecture is on Unit 3b, Plate Tectonics
• Topics to be covered include:
• How Plate Tectonics work
• What a Plate is composed of
• Different Plate Boundaries
• Plate Creation and Destruction

Main Concepts in Plate Tectonics

• Lithospheric plates continually undergo a tectonic cycle of creation and destruction

How We Understand the Earth

• Geologic time, involving thousands, millions, and billions of years, must be used to understand the Earth
• James Hutton introduced the concept of geologic time in 1788
• Everyday changes over millions of years add up to major results
• Natural laws are uniform through time and space

Plate Tectonics

• The lithosphere is broken into plates

What is a Plate?

• A plate consists of the lithosphere, which includes both the crust and the uppermost part of the mantle
• Plates are dragged along with the flowing asthenosphere
• Plate boundaries include:
• Divergence
• Convergence
• Slide past

Plate Composition

• Crust is composed of low-density minerals such as Silicon and Oxygen
• The Mantle has higher density minerals which includes Silicon, Oxygen, Iron, and Magnesium
• The Core is made of Metals that consist of Iron and Nickel
• The Lithosphere is the crust plus the uppermost mantle, composing a rigid plate
• Earthquakes happen here
• The Asthenosphere is within the mantle and is mushy like silly putty, and can flow

Plate Boundaries

• The lithosphere of Earth is broken into plates separated by divergence zones, transform faults, and convergence zones
• Plate edges define Plate boundaries as they interact
• The location of continents relative to plates:
• North America (N AM)
• South America (S AM)
• Eurasia (EUR/ASIA)
• African (AFR)
• Antarctic (ANT)
• Pacific (PAC)
• Australia/India (IND/AUS)
• Philippine (PHIL)
• Nazca (NAZCA)

Plate Tectonics (Movement and Interactions)

• Earthquakes, volcanoes and mountains are typically the result of plate-edge interactions
• Divergence zones are where plates pull apart during seafloor spreading (creation)
• Transform faults are where plates slide past one another
• Convergence zones are where plates collide with one another (destruction or crumpling)

Three Basic Types of Plate Boundaries

• Divergent- Plates diverging from one another
• Convergent-Subduction (ocean-ocean & ocean-continent)
• Convergent-Collision (continent-continent)
• Transform- Plates sliding past one another

Creation and Destruction of Lithospheric Plates

• Melted asthenosphere flows upward as magma
• Magma cools to form new ocean crust, lithosphere, diverges from zone of formation atop asthenosphere (seafloor spreading)
• When an oceanic lithosphere slab collides with another slab, the older, colder, and denser slab subducts under the younger, hotter, and less dense slab
• The subducted slab is reabsorbed into the mantle
• Wilson Cycle takes on the order of 400 million years

Spreading Centers

• At mid-ocean ridges:
• Hot mantle rock rises
• Melt forms under the lithosphere
• Magma rises into a magma chamber
• Lava erupts, adding to the crust
• Plates move apart, cool, and thicken

The Grand Unifying Theory (Tectonics)

• When two plates collide, the denser or colder plate goes beneath the less-dense or warmer plate in subduction zones
• In oceanic plate subduction: Volcanic island arcs are next to trenches such as the Aleutian Islands of Alaska
• In continental plate subduction: Volcanic arcs are located on the continental edge next to trenches like the Cascade Range
• Plate tectonics must involve millions and billions of years of geological activity
• Plate movement is about 1-10 cm/year
• 5 cm/year = 4-5 m over a lifetime
• 50 km in 1 million years
• 5000 km in 100 million years
• Small events add up to big results, also known as uniformitarianism