Plate Tectonics Lecture Notes PDF

Lecture 4: Plate Tectonics… A Unifying Theory 1 ©JoAnna Wendel Quiz 2 Find it under ‘Quizzes’ on UM Learn 10 points Unlimited attempts Highest score kept as graded score Due by Friday Jan 17 at 11:59pm...

Lecture 4: Plate Tectonics… A Unifying Theory 1 ©JoAnna Wendel Quiz 2 Find it under ‘Quizzes’ on UM Learn 10 points Unlimited attempts Highest score kept as graded score Due by Friday Jan 17 at 11:59pm 2 Objectives Last lecture: The rock cycle This lecture: Examine the evidence for continental drift Understand the theory of plate tectonics 3  Earth is a dynamic and evolving planet Quiz 1 Topics 5 7 8 https://earthquakes.volcanodiscovery.com/ 10 Continental Drift Hypothesis 1912 Alfred Wegener proposed that a single supercontinent (Pangaea) broke up to form the modern continents Ideas developed by Alexander Du Toit Our Wandering Continents 1937 Berlin/Art Resource, NY Continental fit Similarity of rock What is the evidence sequences and mountain ranges for continental drift? Glacial evidence 11 Fossil evidence  1.Continental Fit Evidence look the continents like like they fit a puzzle starteplitting By Lennart Kudling - CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=4560703 Fig 3.3 12  2. Similarity of Rock Sequences Fig 3.4 13  3. Glacial Evidence strictions on bedrock glacial Fig 3.5 14  4. Fossil Evidence Fig 3.1 Fig 3.6 15 Lots of evidence, tear or say but… wasn't widean Geologists moved The continents moved, but how? Centrifugal force caused by Earth’s rotation? Precession of the Earth (wobbling of axis)? ‘Tidal argument' based on the tidal attraction of sun and moon (continents floating on water)? 16 Magnetic Reversals and Seafloor Spreading 1962: Hess proposed the theory of seafloor spreading Seafloor separates at oceanic ridges New crust is formed by upwelling magma As the magma cools, the newly formed oceanic crust moves laterally away from the ridge 17 Earth’s Magnetic Field two diff. poles Fig 3.7 18  Earth’s Magnetic Field mag.polesdono- cal with poses it has happened and in the past willhappafuture it poles when mag. reverse to opposite poles cie south mag. pole in north hemi 19 Fig 3.8 Fig 3.9 Fig 3.10 20  Reconstructing Plate Positions Using Magnetic Anomalies Fig 3.21 Seafloor Spreading Confirmed The ocean crust has magnetic anomalies that are both parallel to and symmetric around ocean ridges Evidence indicates new oceanic crust forms along the spreading ridges Deep sea drilling confirms older sediments and fossils are buried deeper Oceanic crust is youngest near spreading ridges; oldest is farthest away 22 Fig 3.11 23 Fig 3.12 24  Observation Theory of plate tectonics Plate tectonics is the unifying theory of geology Invent hypothesis to Makes sense of seemingly disparate explain observation phenomena Helps us understand dynamic forces like volcanoes, earthquakes, and mountain building Devise test of as interrelated and repeating events hypothesis More tests Proposed that large segments of Earth’s outer part Did the hypothesis (lithospheric plates) move relative to one another NO pass the test? YES Continents and ocean basins are part of a lithosphere-atmosphere-hydrosphere system Many successful tests that evolved together with Earth’s interior Theory 25 How did Earth form? The Homogeneous Accretion Theory Fig 1.9 28 The Core Consists of: A small, solid inner region A larger, liquid outer portion Composed of: Iron A small amount of nickel Fig 1.10 29 The Mantle Surrounds the core and is divided into three parts Solid lower mantle Partially molten asthenosphere that overall, behaves plastically and flows slowly Solid upper mantle Composed primarily of peridotite Rock made of the mineral olivine Fig 1.10 30 The Crust Relatively thin outer skin of the Earth Comprises the lithosphere (along with the upper mantle) Consists of thin oceanic and thick continental crusts Fig 1.10 31 What drives plate tectonics? Mid-oceanic ridge Trench Ocean Convection cells Subduction Ridge push Oceanic Continental lithosphere Slab pull lithosphere Cold Convection cell Upwelling Hot Outer core Mantle Inner core Stepped Art 32  Misconception of Convection ▪ The conceptual models of convection cells have changed over time from the old model of a singular convection cell (bottom left) to the modern one with warmer and cooler areas (bottom right). ▪ Convection cells are no longer thought to drive plate motion alone. Fig 4.20a,b Marshak (2022)  Plate Driving Forces: Ridge Push Plate driving forces: ridge push develops because of the gravitational energy associated with the topographic elevation of the mid- ocean ridge. Fig 4.13a,c Marshak (2022)  Plate Driving Forces: Slab Pull Plate driving forces: slab pull develops because old oceanic lithosphere is denser than the underlying asthenosphere, so it sinks. Fig 4.20d Marshak (2022)