Where are the Earth’s tectonic plates and their boundaries? What happens at plate boundaries? How do Earth scientists classify plate boundaries?

Part 1.  Identify the patterns of your area of expertise – volcanology, seismology, geography, geochronology - AT PLATE BOUNDARIES  Describe what you observe – do not interpret what you see, just describe the patterns  Use descriptive terms: Wide or narrow, straight or curved, symmetric or not symmetric, deep or shallow, ridge or valley, active or inactive  Identify 3-5 boundary types; color each on your transparency; define in words

Part 2.  Bring together areas of expertise – volcanology, seismology, geography, geochronology  Correlate your data sets; what collective patterns emerge?  Identify 3-5 boundary types; color each on a master transparency; define in words  10 min

Part 3.  Describe the different types of boundaries  What patterns were related in the different data sets?

 What skills did you use in undertaking this activity?  Historical use …  How might you use it in your classroom?  What might you modify?

Plate Boundaries Where Stuff Happens

Plate Tectonics Theory The upper mechanical layer of Earth (lithosphere) is divided into rigid plates that move away, toward, and along each other Most (!) geologic action occurs at plate boundaries in DISTINCT patterns

Compositional Crust - 2 Mantle Core Physical / Mechanical Lithosphere Asthenosphere Mesosphere

Crust (Compositional)  Two types of crust: Continental Continental 30% of crust30% of crust Granites and Diorites - rich in silicates and feldspars (lighter materials)Granites and Diorites - rich in silicates and feldspars (lighter materials) 40 Km thick40 Km thick Oldest is 3.8 billion years (90% solar system age; missing ~700 m.y.)Oldest is 3.8 billion years (90% solar system age; missing ~700 m.y.) 4.4 billion year old zircons in Western Australia4.4 billion year old zircons in Western Australia Oceanic crust Oceanic crust Basalt - Mg, Fe (heavier materials - relatively)Basalt - Mg, Fe (heavier materials - relatively) 5-10 Km thick5-10 Km thick 200 Ma oldest; 100 Ma average200 Ma oldest; 100 Ma average OphiolitesOphiolites

 Lithosphere PLATES in Plate Tectonics PLATES in Plate Tectonics Upper 200 km Upper 200 km Crust and upper mantle Crust and upper mantle Rigid Rigid  Asthenosphere 200 km to ~700 Km 200 km to ~700 Km Upper mantle Upper mantle Hi temperatures / high pressure: little strength; ductile / plastic - NOT A LIQUID! Hi temperatures / high pressure: little strength; ductile / plastic - NOT A LIQUID! Plates moving on this Plates moving on this Magma generation Magma generation  Mesosphere Also hot; strong due to pressure Also hot; strong due to pressure Lithosphere / Asthenosphere (Mechanical)

3 Basic Boundary Interactions 5 to 6 Basic Boundary Types

1. Divergent Boundaries Mid-AtlanticRidge North American Plate Plate EurasianPlateEurasianPlate Volcanic activity in fissures, some volcanos Shallow earthquakes, on plate boundary Young crust, symmetrical around boundary Ridge Rocks?

South American Plate Nazca Plate Antarctic Plate

Andes Mountains

2. Convergent Boundaries (a) Ocean-continent convergence Nazca Plate AndesMountains SouthAmericanPlateSouthAmericanPlate Peru-Chile Trench Volcanos tight, parallel boundary, landward Shallow to deep earthquakes Age varies on one side of the boundary; not symmetrical Trench, mountain chain Rocks?

Foreshadowing … Many on Earth Relatively small … but mighty …

2. Convergent Boundaries (b) Ocean-ocean convergence Mariana Islands Marianas Trench Pacific Plate PhilippinePlatePhilippinePlate Volcanos tightly spaced, parallel boundary, arc Shallow to deep earthquakes Age varies on one side of the boundary; not symmetrical Trench, volcanic island chain Rocks?

Eurasian Plate Indian Plate

Himalaya Mountains

Tibetan Plateau Himalayan Mtns. Mt. Everest

2. Convergent Boundaries (c) Continent-continent convergence TibetanPlateau Indian-Australian Plate EurasianPlateEurasianPlate HimalayanMountains Volcanos rare, dispersed Shallow (to medium) dispersed earthquakes No age data High mountain chain Rocks?

3. Transform-Fault Boundaries North American Plate Pacific Plate Volcanos dispersed, most on one side Earthquakes complex, shallow (to medium) on both sides Age data not symmetrical, one side of boundary Complex topography, wide mountains and basins Rocks?

Plate Tectonics The upper mechanical layer of Earth (lithosphere) is divided into rigid plates that move away, toward, and along each other Most (!) geologic action occurs at plate boundaries in DISTINCT patterns

What’s Driving Plate Tectonics on Earth?

Mantle  85% volume of Earth  Density g/cm 3  Probably material such as Peridotite (lots of heavy olivine - Fe, Mg)  Solid; high pressure  slow, creeping, viscous movement - convection  Samples from kimberlites, xenoliths in volcanic eruptions, basalt composition; lab experiments

Core  15% of Earth’s volume / ~half of diameter of Earth  Outer core Molten Molten Density of pure iron or nickel/iron; ~2x density of mantle Density of pure iron or nickel/iron; ~2x density of mantle Convection … Earth’s magnetic field Convection … Earth’s magnetic field  Inner core Solid (very hot, but higher pressure than outer core) Solid (very hot, but higher pressure than outer core) Density of nickel/iron (~13 g/cm 3 ) Density of nickel/iron (~13 g/cm 3 ) Conducts heat - cooling Conducts heat - cooling ~ Size of Moon (~70% of Moon) ~ Size of Moon (~70% of Moon)

Earth’s Magnetic Field  Magnetic dipole … a bar magnet tilted ~11 degrees  Generated by eddies in the conductive liquid of the outer core – currents create magnetic fields  Changes over time – north magnetic pole wanders, north and south reverse  Rather important to life … really important to geology

What’s Driving Plate Tectonics on Earth?

How Did Earth (and other planets) Get Layers?