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Understanding Plate Tectonics: Evidence and Causes of Geological Motion

This section explores the fundamental concepts of plate tectonics, including paleomagnetism, earthquake patterns, and hot spot activity. It discusses how rocks become magnetized in accordance with Earth's magnetic field and presents evidence for plate movement through seafloor spreading and ocean drilling. Additionally, it examines the mechanisms driving plate motion, such as convection in the mantle, slab pull, and ridge push. This comprehensive understanding is crucial for grasping the dynamic nature of Earth's geological processes.

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Understanding Plate Tectonics: Evidence and Causes of Geological Motion

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  1. TESTING PLATE TECTONICS Sections 9.4 and 9.5

  2. TESTING PLATE TECTONICS • Paleomagnetism • When a rock forms, it becomes magnetized in the direction parallel to Earth’s existing magnetic field • Normal polarity – when rocks show the same magnetism as the present magnetic field • Reverse polarity – when rocks show the opposite magnetism as the present magnetic field

  3. EVIDENCE FOR PLATE TECTONICS • The discovery of strips of alternating polarity, which lie as mirror images across ocean ridges, is among the strongest evidence of seafloor spreading

  4. EVIDENCE FOR PLATE TECTONICS • Earthquake Patterns • Scientists discovered a close link between earthquake origins and ocean trenches • Earthquakes occur only within the subducted slab of oceanic lithosphere • Ocean Drilling • Youngest oceanic crust is at the ridge crest, the oldest crust is at the continental margins • Data on the ages of seafloor sediment confirmed the seafloor spreading hypothesis

  5. EVIDENCE FOR PLATE TECTONICS • Hot Spot (Volcanic area) • A concentration of heat in the mantle produces magma, which rises to Earth’s surface creating volcanic mountains • Hot Spot evidence supports the theory that plates move over Earth’s surface Hawaiian Islands

  6. Causes of Plate Motion • Convection occurring in the mantle, specifically asthenosphere, is the driving force for plate movement • Convective flow is the motion of matter resulting from changes in temperature • Warm, less dense material rises • Cool, more dense material sinks • The unequal distribution of heat within Earth causes convection in the mantle, which drives plate motion

  7. CAUSES OF PLATE MOTION Slab-pull occurs when the cool, dense oceanic crust sinks into the mantle and “pulls” the lithosphere along Ridge-push causes oceanic lithosphere to slide down the sides of the oceanic ridge under the pull of gravity

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