Geo 1330 - Hauptvogel, Lecture 3: Introduction to Plate Tectonics
Geo 1330 - Hauptvogel, Lecture 3: Introduction to Plate Tectonics GEOL 1330
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This 6 page Class Notes was uploaded by Julian Quesada on Sunday February 7, 2016. The Class Notes belongs to GEOL 1330 at University of Houston taught by Dr. Daniel Hauptvogel in Spring 2016. Since its upload, it has received 67 views. For similar materials see Physical Geology in Geology at University of Houston.
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Date Created: 02/07/16
GEOL 1330 LECTURE 3 – INTRODUCTION TO PLATE TECTONICS Alfred Wegener: Continental Drift -Alfred Wegener - The Father of Continental Drift -First proposed his continental drift hypothesis in 1915 -Continents are drifting together or apart -Published in his book -Continents "drifted" to present positions -200 million years ago, all continents were together in one supercontinent -Called Pangaea -How did Wegener fit the continents together? -Geometric Fit of the continents -Matching Fossils on different continents that are oceans apart -Matching Geology: Rock types found in one area (exact chemistry of the rocks and ages of the rocks) match exactly with rocks found in other continents separated by oceans -Paleoclimatic Evidence: Evidence of glaciers are found on one continent and their matching missing part are found on a different continent Harry Hess: Seafloor Spreading -Harry Hess: The father of sea-floor spreading, 1962 -Built on what Wegener discovered -Noticed a topography to the ocean floor -There were mountains and trenches on the ocean floor -Using continental drift hypothesis, Harry Hess developed an idea for the production and destruction of oceanic crust -Top Hat Question -Where on the map (world map) do you think new crust is being created -Answer: Pacific Ocean off the west coast of N. and S. America Atlantic Ocean between the Americans and Europe/Africa In the Indian Ocean -Seafloor formed at mid-ocean ridges -Seafloor consumed at trenches -Process driven by convection in the mantle -Convection definition: The slow motion of Earth's solid silicate mantle caused by convection currents carrying heat from the interior of the Earth to the surface. The Theory of Plate Tectonics -A model explaining how the Earth works -Referred to as the grand unifying theory in geology -A set of ideas explaining the overserved motion of Earth's lithosphere through the mechanisms of subduction and seafloor spreading, which in turn, generate Earth's major features, including continents and ocean basins -The theory of plate tectonics states -The Earth's lithosphere is broken into several plates that move and change shape along their boundaries in a predictable way -The outermost shell of the earth is the lithosphere -Definition: Crust and upper, rigid mantle -Crust is part of the lithosphere but the lithosphere is not the crust -The lithosphere rides over a weak, partly melted portion of the mantle - asthenosphere -The lithosphere is broken into a series of large plates that move relative to each other -Most of the deformation and volcanic activity on earth occurs along plate boundaries -The theory provides explanations for: -Earth's major surface processes -The geologic distribution of earthquakes, volcanoes, and mountains -Distribution of ancient organisms and mineral deposits -Remember the 2 types of crust -Oceanic - 2-15km thick, density 3.0g/cm^3 -Continental - 20-70km thick, density 2.7g/cm^3 -Top Hat Question -What do you think would happen if continental crust collided with oceanic crust? -Answer: The oceanic crust would sink beneath the continental crust Types of boundaries -Divergent - plates move away from each other -Mid Ocean Ridges -Characterized by the creation of new oceanic crust -Convergent - plates move toward each other -Characterized by the consumption of old oceanic crust by the process of subduction -Subduction: When one plate sinks below another plate -Oceanic crust is destroyed (recycled back into earth) -Transform - When plates slide past each other -Oceanic crust is neither created nor consumed -San Andreas Fault Divergent Plate Boundaries -Plates diverge or spread apart from one another -As plates move apart the space between them is filled with molten rock whereby new ocean crust is formed -Seafloor spreading -Top Hat Question -Which of the following is not a type of boundary between two tectonic plates? -Options: A) Convergent/ B) Divergent/ C) Coastal/ D) Transform -Answer: Coastal -What starts a plate wanting to move? -Molten material from the mantle starts to move up (upwelling), pushing the earth up, creating a bulge/hill -The two plates will start to move apart as the bulge gets bigger and the crust above the bulge gets thinner -When raised high enough, the bulge/hill will split -Eventually a mid ocean ridge is created along with a rift valley where the molten material will rise and create new sea floor -Divergent boundaries create oceans/lakes/seas (Ex: Red Sea is a new forming ocean) -Youngest ocean floor will be in the middle of the ocean where the rift valley is, with the oldest ocean floor being near the coast -No ocean floor older than 200 million years old, it is recycled through subduction Convergent Plate Boundaries -Ocean-Continent -Convergent plate boundary where oceanic lithosphere is subducting beneath continental lithosphere -Creates trench where the oceanic crust begins to sink beneath the continental crust into the mantle -Crust begins to melt in the mantle, turns into magma (liquid rock beneath surface) which begins to rise to the surface because it has a lower density than its surroundings -Water driven from subducting plate triggers melting in the mantle by lowering the melting point of the rock (Partial Melting) -Begins to form volcanoes (not all volcanoes, but most) -Continental Volcanic Arc: -Earthquakes associated with this boundary -Crust moves past each other in a jerky motion to overcome the friction of the rock on rock, creating a slippage -This slippage what creates earthquakes -Ocean-Ocean -Convergent plate boundary involving two slabs of oceanic lithosphere -More dense of the two oceanic crusts is the one that sinks -Younger crust is expanded, warm, and less dense -Older crust is contracted when it cools and more dense -This process creates volcanoes in the middle of the ocean -Except Hawaii -The crust that sinks beneath is melted and turned into magma and then rises, creating continental crust -This is the only way to create continental crust -Volcanic Island Arc: -Ex: Japan -Why are the chain of islands curved? -The earth is round -Continent-Continent -Continental collisions occur along convergent plate boundaries when both plates are capped with continental crust -Occurs where there was once an ocean -The subduction zone between the two plates subducted everything, the ocean is gone. -The two continental plates suture on to each other (no more visible boundary) -Not a lot of subduction, both are very thick, not very dense -Creates mountains -Ex: Himalayas - India moved up into Asia -India is moving move beneath Asia -Crust is extremely thick where the two plates collide Transform Plate Boundaries -Plates move side by side -Mid-Atlantic Ridge -At Mid-Ocean Ridges, transform and divergent plate boundaries make a broken pattern -San Andreas Fault -At one time, it was a subduction zone -Sierra Nevada mountains was volcanic at one time -Earthquakes associated with Transform faults, no volcanoes Types of Boundaries (Pt II) -Slab Pull - Results from the sinking of a cold dense slab of oceanic lithosphere and is the major driving force of plate motion -Mantle Convection - Enhances plate motion when the velocity of the asthenosphere exceeds that of the overlying plate. -Ridge Push - Gravity driven force that results from the elevated position of the ridge -Serves to enhance plate motion
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