Geology Plate tectonics Lab 1

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Edmonds Community College *

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Geology

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Apr 3, 2024

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1. What kind of plate boundary separates Australia from Antarctica? : A) A. Mid-ocean ridge, or divergent boundary 2. What kind of plate boundary separates the Caroline Plate from the Pacific Plate? : D) Major Fault, or Transform Boundary. 3. What kind of plate boundary separates the Nazca Plate from the South American Plate? : B) Subduction Zone, or Convergent Boundary. 4. The mid-ocean ridges are marked by double-headed arrows to indicate the process of seafloor spreading. The number next to each arrow gives the spreading rate. Which mid-ocean ridge is spreading the fastest? : D) East Pacific Rise 5. Which mid-ocean ridge is spreading the slowest? : D) Southwest Indian Ocean Ridge 6. What kind of plate boundary separates the Juan de Fuca Plate from the Pacific Plate? : C) Subduction zone, or convergent boundary 7. Which plate boundary: A, B or C is diverging at the fastest rate? : A is diverging at the fastest rate 8. What evidence did you use to answer the previous question? : I used the 'Age of the Ocean Floors' to look at the color-coded ages of the ocean floor and understand the plate boundaries. 9. Using the information in these 4 images, what type of plate boundary is the Tonga-Pacific Plate boundary? Please be very specific about which plates are oceanic or continental and the direction of movement relative to each other. : The Tonga-Pacific Plate boundary is a convergent boundary where both plates are oceanic. Specifically, it is a subduction zone, with the Pacific Plate subducting beneath the Tonga Plate. This is indicated by the presence of deep earthquakes (blue dots) extending beneath the Tonga Plate, signifying the descent of the Pacific Plate into the mantle. The presence of volcanoes along the boundary (red circles) further supports this interpretation, as subduction zones are associated with volcanic activity. 10. What evidence from these 4 pictures did you use to answer the previous question? : The distribution of earthquakes, with shallow, medium depth, and deep earthquakes occurring along the boundary. Deep earthquakes indicate the presence of a subducting slab.
The location of volcanoes along the boundary, which are commonly associated with subduction zones. The orientation of the boundary between Tonga and Pacific Plates, which is depicted by the red line in the center image, aligns with the characteristics of a convergent boundary where oceanic plates converge and one plate is forced beneath the other. 11. Based on these two images and your understanding of slab pull, which subduction zone do you expect to be converging at a faster rate? : I would expect the Nazca-South American Subduction Zone to be converging at a faster rate. This is because the Nazca Plate is significantly denser and heavier than the Juan de Fuca Plate in the Pacific Northwest Subduction Zone. Therefore, the slab pull force exerted by the subducting Nazca Plate would likely be stronger, leading to a faster convergence rate between the Nazca and South American Plates. 12 What evidence did you use to answer the previous question? : The age of the oceanic crust (depicted by the color gradient from deep red to lighter shades) is younger at the Nazca-South American Subduction Zone compared to the Pacific Northwest Subduction Zone. Younger oceanic crust typically correlates with faster convergence rates due to higher rates of seafloor spreading at mid-ocean ridges. The deeper shade of red (representing the youngest crust) at the Nazca-South American Subduction Zone indicates a more active spreading ridge, suggesting a higher rate of slab pull force exerted by the subducting Nazca Plate. The angle and steepness of the subduction zones may also influence the effectiveness of slab pull. A steeper subduction angle, which is often associated with faster convergence rates, would enhance the slab pull force exerted by the denser slab. 13. As one travels to the north along the western margin of the South American Plate, the plate boundary changes. Using the color-coded depth scale, describe what happens to the angle of dip of the plate boundary between -30°S and -20° latitude. Hint: Focus on the different colors and the distance they are from the edge of the continent. If you just focus on the Orange (shallow), Green (intermediate), and Blue (deep), you can figure out the answer. : A. The angle is getting steeper 14. Which tectonic plate is composed of both continental crust and oceanic crust? : B. Juan de Fuca Plate. 15. Plates move as rigid bodies, yet the North American Plate is moving at different rates in different places. Why? : B. Plates move rotationally.
16. Identify your plate boundary by the name of the two tectonic plates as well as the type of boundary (convergent, divergent, or transform) and the type of plates (oceanic or continental) at that boundary. The San Andreas Fault is a transform boundary. Here are the details: Tectonic Plates Involved: The San Andreas Fault marks the boundary between the Pacific Plate and the North American Plate. Type of Boundary: The San Andreas Fault is a transform boundary. At this boundary, the plates slide horizontally past each other. Type of Plates: The Pacific Plate is oceanic. The North American Plate is continental. Description: The San Andreas Fault is a prominent fault system that extends for approximately 800 miles (1,300 kilometers) through California. It runs from the Gulf of California in the south to the Mendocino Triple Junction in the north. Along this fault, the Pacific Plate moves northwestward relative to the North American Plate. The motion is primarily right-lateral strike-slip, meaning that the plates move horizontally past each other. The San Andreas Fault is responsible for numerous earthquakes in California, including the famous 1906 San Francisco earthquakes
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