Geological Disasters & Society: Plate Tectonics

Welcome to Geos 218 Geological Disasters & Society Today: Unit 3b Plate Tectonics What is a Plate Plate Boundaries Plate Creation & Destruction 1 Main Concepts in Plate Tectonics: Lithospheric plates & tectonic cycle Plates are conti...

Welcome to Geos 218 Geological Disasters & Society Today: Unit 3b Plate Tectonics What is a Plate Plate Boundaries Plate Creation & Destruction 1 Main Concepts in Plate Tectonics: Lithospheric plates & tectonic cycle Plates are continually created and destroyed Lithosphere 2 1  How We Understand the Earth Must think in terms of geologic time rather than human time – thousands, millions and billions of years In 1788, James Hutton introduced concept of geologic time: – “No vestige of a beginning, no prospect of an end.” – Everyday changes over millions of years add up to major results Uniformitarianism: natural laws are uniform through time and space; present is the key to the past Contrast to previously believed catastrophism Currently modified actualism: rates of Earth processes vary 3 Main Concepts in Plate Tectonics: Evidence for plate tectonics Tectonic Plates Lithosphere/asthenosphere Sea Floor Spreading 3 Main Types of Plate Boundaries Divergent Convergent subduction zone collision zone Transform 4 2  Plate Tectonics Lithosphere of Earth is broken into plates: 5 What’s a plate? Plate = Lithosphere = Crust + Uppermost Mantle Dragged along with flowing Asthenosphere Crust Lithosphere Mantle 6 3  What is a Plate? Draw a profile/layer cake view Surface Depth 7 What is a Plate? Geochemical/Density Layers Physical Layers Temperature Surface Crust = low density minerals (Si + O) Lithosphere = crust + uppermost mantle à RIGID layer = PLATE! Cool ~ 100km thick EQ happen here! Asthenosphere = within the mantle MUSHY (like silly putty), can flow! ~ 100km thick Depth Mantle = higher density minerals (more metals) Si + O + Fe + Mg Lower mantle = SOLID silicon, oxygen, iron, magnesium ~2500 km thick Core = metals Outer Core = LIQUID (iron (Fe) / nickel (Ni)) HOT Inner Core = SOLID Layer thickness NOT to scale! Layer thickness NOT to scale! 8 4  Main Concepts in Plate Tectonics: Lithospheric plates & tectonic cycle 9 In plate tectonics the term "plate" refers to the __________. A. continental crust B. crust and the entire mantle C. oceanic crust D. Strong/rigid Earth above the asthenosphere, known as the “lithosphere” 10 5  Plate Tectonics Lithosphere of Earth is broken into plates separated by: divergence zones, transform faults, convergence zones 11 Plate Tectonics Lithosphere of Earth is broken into plates separated by: divergence zones, transform faults, convergence zones 12 6  Plate Tectonics Lithosphere of Earth is broken into plates separated by: divergence zones, transform faults, convergence zones 13 Plate Boundaries Lithosphere of Earth is broken into plates separated by: divergence zones, transform faults, convergence zones EUR/ASIA N AM PHIL PAC Cocos AFR IND/AUS NAZCA S AM IND/AUS ANT 14 7  Plate Boundaries Plates are defined by their EDGES! EUR/ASIA N AM PHIL PAC Cocos AFR IND/AUS NAZCA S AM IND/AUS ANT 15 Study Question How many plates are in this picture? A. 1 3 1 2 B. 2 C. 3 D. 4 16 8  Plate Tectonics Lithosphere of Earth is broken into plates Plate Tectonics: Study of movement and interaction of plates Zones of plate-edge interactions are responsible for most earthquakes, volcanoes and mountains Divergence zones – Plates pull apart during seafloor spreading (creation) Transform faults – Plates slide past one another Convergence zones – Plates collide with one another (destruction or crumpling) 17 Three Basic Types of Plate Boundaries Divergent Convergent-Subduction (ocean-ocean & ocean- continent) Convergent-Collision (continent-continent) Transform 18 9  Main Concept in Plate Tectonics Creation and destruction of creation lithospheric plates creation i on uct s tr de 19 Plate Tectonics Tectonic cycle: Melted asthenosphere flows upward as magma Cools to form new ocean crust (lithosphere) New oceanic lithosphere (slab) diverges from zone of formation atop asthenosphere (seafloor spreading) When slab of oceanic lithosphere collides with another slab, older, colder, denser slab subducts under younger, hotter, less dense slab Subducted slab is reabsorbed into the mantle Cycle (Wilson Cycle) takes on order of 400 million years https://www.youtube.com/watch?v=I_q3sAcuzIY 20 10  Animation: Spreading Center https://www.iris.edu/hq/inclass/animation/plate_boundary_divergent_fastspreading_ridge 21 Study Question New ocean crust is created at: A. Subduction zones B. Spreading centers C. Transform faults D. All of these 22 11  Figure 2.27 https://youtu.be/i8Zo1_FN6xw?t=900 Naked Science “Colliding Continents” video clip, ~15:00-19:00 23 Figure 2.27 https://youtu.be/i8Zo1_FN6xw?t=900 Naked Science “Colliding Continents” video clip, ~15:00-19:00 24 12  The Grand Unifying Theory Tectonic cycle: When two plates collide, denser (colder, older) plate goes beneath less-dense (warmer, younger) plate in subduction – Oceanic plate beneath oceanic plate: Volcanic island arc next to trench (Aleutian Islands of Alaska) – Oceanic plate beneath continental plate: Volcanic arc on continent edge next to trench (Cascade Range) Plate tectonics requires time perspective of millions and billions of years – Plate movement may be 1-10 cm/year 5 cm/yr = 4-5 m during your life, = 50 km in a million years (my) = 5000 km in 100 my – Uniformitarianism: small events add up to big results 25 13