Presentation on theme: "Plate Tectonics Chapter - 8 The lithosphere is broken into rigid plates that move in relationship to one another on the asthenosphere (see page 712-713."— Presentation transcript:
Plate Tectonics Chapter - 8 The lithosphere is broken into rigid plates that move in relationship to one another on the asthenosphere (see page in textbook)
Objectives: ◦Identify the evidence that A. Wegener used to support Continental Drift ◦Explain how the theory of Plate Tectonics helps predict the locations of earthquakes and volcanoes ◦ ◦AZ Science Standard: Demonstrate the relationships among earthquakes, volcanoes, mountain ranges, mid-ocean ridges, deep sea trenches, and tectonic plates
8.1 What is Plate Tectonics? The theory that describes the formation, movements, and interactions of these plates. The lithosphere is broken into rigid plates that move in relationship to one another on the asthenosphere.
8.1 What is Plate Tectonics? The lithosphere is our crust that sits on top of the asthenosphere.
8.1 What is Plate Tectonics? Plate Tectonics Theory ◦Early evidence included shapes of the continents (South America and Africa) ◦Similar fossil record ◦Similar locations of rivers flowing into the ocean ◦Similar plants growing ◦Similar coastal rock formation. Initially, there was little acceptance of Wegner’s theory because he couldn’t explain why they moved.
The theory of plate tectonics helps explain the locations of earthquakes and volcanoes.
Therefore, characteristic features associated with plate boundaries: ◦Earthquake activity ◦Volcanic activity ◦High heat flow 8.1 What is Plate Tectonics?
DEFINE: Plate Tectonics - a theory that describes the formation, movement, and interactions of the plates on the lithosphere. Continental Drift – movement of continents. Mid-Ocean Ridge - a long chain of volcanic mountains on the ocean floor. 8.1 What is Plate Tectonics?
What observations support the continental drift hypothesis? ◦Earthquakes and volcanoes occur in concentrated belts that correspond to present tectonic plate boundaries. 8.1 What is Plate Tectonics?
What evidence in support of plate tectonics is provided by studies of the ocean floor? ◦Magnetic reversals in rocks on either side of the Mid-Atlantic Ridge; High heat flow along ridges; Youngest crust is close to ridge axis. 8.1 What is Plate Tectonics?
Objectives: Discuss verbally the differences among the three types of plate boundaries Contrast the three different types of convergent boundaries
8.2 Types of Plate Boundaries Minerals in igneous rocks can show the direction of Earth’s polarity field at the time the rocks were formed.
8.2 Types of Plate Boundaries Transform Boundary
8.2 Types of Plate Boundaries Convergent Boundary
8.2 Types of Plate Boundaries Divergent Boundary
8.2 Types of Plate Boundaries Mid Atlantic Ridge ◦Hydrothermal vents ◦New rocks are forming ◦Earthquakes occur here
8.2 Types of Plate Boundaries Types of Plate Boundaries summary BoundaryProcess involved FeaturesCurrent Example DivergentSea-floor spreading Mid-ocean ridges Rift valleys Earthquake activity Volcanic activity Mid-Atlantic Ridge East pacific Rise ConvergentOcean-ocean Deep sea trenches Volcanic island arcs Earthquake activity Island of Indonesia Mariana Islands Ocean-Continent subduction Deep sea trench bordering continent Volcanoes along coast-line Earthquake activity Western coast of South America TransformPlates sliding past each other Earthquake activity San Andreas Fault North Anatolian Fault (Turkey) Fracture zones along mid- ocean ridges
8.2 Types of Plate Boundaries New oceanic crust is formed at a divergent boundary when: ◦Step 1 - Molten rock forces its way upward into the rifts that form when two lithospheric plates separate. ◦Step 2 - As the molten rock cools, new oceanic crust forms. ◦Step 3 - The older oceanic crust moves away from the mid-ocean ridge.
8.2 Types of Plate Boundaries Two different types of subduction boundaries are: ◦Oceanic-oceanic plate convergence – two features are a deep-sea trench and a volcanic island arc on the overriding plate. (Marianna trench) ◦Oceanic-continental plate convergence – a deep-sea trench and an inland mountain chain and volcanoes characterize this type of subduction boundary. (the Andes)
8.2 Types of Plate Boundaries Describe what happens at a collision boundary, identify a collision boundary: ◦Two Continental plates collide, forming a single, larger continent and pushing up the crust to form a mountain range. ◦Ex: Himalayan and Appalachian Mountains
8.2 Types of Plate Boundaries When two oceanic plates converge, the denser plate is subducted. A chain of volcanoes commonly forms when an oceanic plate subducts under a continental plate. Fracture zones that offset portions of mid- ocean ridges are examples of divergent boundaries.
8.2 Types of Plate Boundaries Describe the movement of plates at a transform boundary, give example. ◦Plates slide past each other at a transform boundary. ◦Ex: San Andreas fault; and the fracture zones along mid-ocean ridges.
Objectives: Discuss mantle convection as a possible cause of plate movements Compare and contrast ridge push and slab pull
8.3 Causes of Plate Movements Three hypotheses for plate movement: ◦Mantle convection - convection currents within the mantle are pushing the plates. ◦Ridge push - hot mantle at ridge is lighter and lifts up at the ridge, as it spreads, it cools, and denser material slides off ridge. ◦Slab pull – sub-ducted material “pulls” the plate with it as it slides downward under other plate.
Explain how Earth’s landmasses have changed positions over the past 200 million years Discuss the roles of plate tectonics, igneous activity, and deposition in the formation of continental landmasses
8.4 Plate Movements and Continetal Growth The breakup of Pangaea is a process that is continuing today.
8.4 Plate Movements and Continetal Growth North American Craton ◦An expanse of ancient rock at the core of the North American Continent formed 2.5 billion yrs ago.
8.4 Plate Movements and Continetal Growth Sources of Growth Material ◦Deep sea sediments most likely contribute to continent growth by being scraped off in a subduction zone and left at the surface. ◦Igneous rock from plutons and volcano ash, lava, and rock material. ◦Terranes are large blocks of lithospheric plates that have been moved over thousands of kilometers and attached to the edge of a continent – three characteristics: 1.Each terrane block is bound by major faults 2.Rocks and fossils found in the terrane do not match those of neighboring terranes 3.Magnetic record found in the terrane does not match that of neighboring terranes.
8.4 Plate Movements and Continental Growth Density plays a big part in plate tectonics Basic density info: ◦Density is mass per unit volume ◦Usually as grams per cubic centimeter ◦g/cc ◦An object that weighs 12 grams and takes up 6 cubic centimeters has a density of (12grams/6cc)=2g/cc