PLATE TECTONICS Theory of Continental Drift, Plate Boundaries

This activity requires you to discuss with a partner

Quick Review **Discuss with your partner the definition of: Lithosphere Asthenosphere Plate Tectonics

Quick Review Lithosphere Lithosphere  Crust and the upper part of the mantle  Broken up in rocky, rigid mass called LITHOSPHERIC PLATES

Quick Review Asthenosphere Asthenosphere  Top part of mantle  Molten (melted)  Fluid

Quick Review Plate tectonics Plate tectonics Lithospheric plates move around SLOWLY on the fluid asthenosphere At PLATE BOUNDARIES (where the plate meet), plates interact in many ways E.g. Collide (Bump into each other), Diverge (Go away from each other), slide past each other, go on top/ below one another

Theory of Continental Drift Developed by German meteorologist Alfred Wegener ( )

Theory of Continental Drift Continents have not always been at the present position, but have “drifted” to these locations over millions of years All continents joint together to form Supercontinents S Since Earth was formed, supercontinentS have been broken and formed MANY TIMES

Theory of Continental Drift PANGAEA  “Pan”=all “Gaea”= World  Most recent supercontinent  Formed 250 million years ago  Started pulling part 200 million years ago

Evidence for Continental Drift 1. The Jigsaw Fits!  Matching coastline of South America & Africa

Evidence for Continental Drift 2. Matching Geological Structures and Rocks  Mountain ranges that begin in one continent, end at coastline, and continue across another continent  Similarities in folds and rock ages in different continents that are separated

Evidence for Continental Drift 3. Fossil Evidence E.g. Mesosaurus  Only found in 2 small geographic regions (SE South America and SW Africa)

E.g. Glossopteris (Fern)  Found in small regions of South America, Africa, India, Antarctica, and Australia Evidence for Continental Drift Wegner wondered how this is possible!

Evidence for Continental Drift 4. Glacier Evidence  Glacier Deposits are found in tropical places!! (Glacier are big sheets of ice only found in cold weather)  Coal beds are found in Antarctica!! (Coal is created by decomposition of tropical swamp)

Evidence of Continental Drift Wegener’s Conclusion: Continents were once in completely different position on Earth, and have moved to their present position Rodina Supercontinent (1.2 bya)

Theory of Plate Tectonics Wegener’s Theory of Continental Drift has ONE MAJOR PROBLEM:  He does not understand HOW the continents moved.

Theory of Plate Tectonics After Alfred Wegener died, oceanographer discovered Mid-Atlantic Ridge  Thin mountain range under water (ocean floor)  Striped pattern found to either side of ridge  Stripes alternate north and south polarity

Theory of Plate Tectonics Discuss : How was the Mid Atlantic Ridge formed? So what does the Mid Atlantic Ridge prove (support)

Theory of Plate Tectonics ** Let’s look the Mid-Atlantic Ridge using Google Earth** *Ms. Yu will also show you a demo on Mid-Atlantic Ridge** =)

Theory of Plate Tectonics

- Plates flow around due to Convection Current in asthenosphere - Radioactive materials deep in the mantle create hot areas (less dense)  Magma force to the surface Plate Boundaries Discuss: What are convection currents? (Science 8, 9?)

**Discuss: How do you think plates can interact with each other? Plate Boundaries

Divergent Plate Boundaries Plates move away from each other Magma rise  push old material aside  cool  become new lithospheric material Forms Ocean Ridges at Spreading Centre and Rifts (land)

RIFT

Convergent Plate Boundaries 1. OCEANIC-CONTINETAL COLLISION Subduction Zone  oceanic plate (more dense) slides under continental plate Extra material from subduction plate is melted off Trench formed Can form Volcanoes, Earthquakes & Mountains

Convergent Plate Boundaries At Subduction Zone, SLAB PULL occurs  The plate that is subducting is actually pulling the rest of the plate with it  Slab pull adds to the force from convection currents

Convergent Plate Boundaries 2. OCEANIC-OCEANIC Subduction  one plate will be FORCED under another Cause earthquakes Form Volcanoes and Island Arc (chains of islands in the ocean formed from convergent plates collisions) E.g. Japan, Aleutian Islands (Alaska)

Convergent Plate Boundaries 3. CONTINENTAL- CONTINENTAL COLLSION Plates collide, crumble and folds Mountain Building E.g. Mount Everest in Himalayas

Transform Plate Boundaries Plates slide past one another, moving in opposite directions Produce large, shallow earthquakes E.g. San Andreas Fault in California (North American plate sliding past Pacific Plate)

Vancouver, British Columbia ** Discuss: What type of plate boundaries do you think we are on right now? Convergent: Oceanic- Continental Collision Juan de Fuca Plate (oceanic) subducts under North American Plate (continental) Rocky Mountains, Cascade Mountain volcanoes, Earthquakes Google Earth

Volcano RING OF FIRE Along edges of Pacific Ocean 75% of the Earth’s active volcanoes

Volcano COMPOSITE VOLCANOES Cone shape volcano Recurring eruptions (ash and lava) build up to form strata Thick magma that trap gas  explosive eruptions Subduction zone E.g. Mt. St. Helen (October 2004) Video

Mt. Garibaldi

Mt. Fuji, Japan

Volcano SHIELD VOLCANO Form at HOT SPOT (weak part of plate where molten material can burst through) Magma are more fluid Largest volcanoes on Earth! E.g. Hawaiian Volcanoes

Hawaiian Volcano- View of Crater

Volcano RIFT ERUPTIONS Spreading centre or rifts at divergent boundaries May produce lots of lava