Learning Exercise 2.docx

Dynamic Earth GEOL-1500 Spring 2024 Plate Tectonic Mechanisms and Driving Forces Learning exercise Name: Haley Young Date: 1/30/23 Learning Goals: What is plate Tectonics? Continental drift and sea floor spreading How paleo-magnetism works? Characteristics of oceanic vs. continental plates What are the different types of plate boundaries? How to measure plate motion rates? What are hot spots? Questions: Part 1: Plate tectonics and continental drift 1) Describe the main elements of the theory of Plate tectonics? The sea floor spreading and continental drift created by the plate tectonics 2) Name and discuss three lines of geologic evidence that support continental drift. Alfred Wegener has lines of geologic evidence for continental drift, 3 of them being fit of the continents, locations of past glaciations, and the distribution of fossils. 1

3) Why wasn’t Alfred Wegener’s initial model of continental drift accepted by the larger scientific community? His initial model of continental drift wasn’t accepted because he provided no reason on how the earth could have shifted, just evidence that it did. Part 2: Paleomagnetism and Sea floor spreading 4) How is the Earth’s magnetic field generated? Draw a picture of the Earth showing the magnetic field. The Earth’s magnetic field was generated in the fluid part of the outer core from electrical currents moving through iron. 5) What is magnetic inclination? The angle at that the geomagnetic field is tilted concerning the surface of the earth. 6) What is magnetic declination? The circumference of the angle that is on the earths surface 7) How can measuring remnant magnetic inclination tell us about where a rock formed on Earth? It can tell you how much magnetic field of the earth in the past and where the plates were as well. 8) If a basalt flow was found to have a paleomagnetic remnant inclination of 5 deg. where would it have likely formed? 2

Ocean Basin 9) What is an apparent polar wander curve? The motion of the rotation axis when relevant to the continent depending the movement of the north and south poles 10) How long ago did the last magnetic reversal occur? 780,000 years ago 11) What is a linear magnetic anomaly? Draw a picture of linear magnetic anomalies surrounding a mid-ocean ridge. Include three periods of normal and reversed polarity. Linear magnetic anomaly is when the poles switch from north to south and its shown on the ocean floor 12) How can linear magnetic anomalies be used to date oceanic crust? By measuring present-day magnetic fields and then analyzing the magnetic anomalies that remain Part 3: Plate tectonic rates 13) What is the average mid-ocean ridge spreading half-rate at the Mid-Atlantic ridge over the past 10 million years? Use the diagram below and give your answer in cm/yr. R=D/T 1 km = 100,000 cm 8 cm/yr 3

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14) What is the oldest crust in the Atlantic Ocean? Is the north Atlantic or South Atlantic older? Mid Atlantic Ridge, North is the oldest 15) Below is a map of the Juan de Fuca Ridge showing linear magnetic anomalies and the Pacific coast of North America. What is the rate of sea floor spreading over the past 8 million years? 4

Show work below: ? 16) In the Q14 diagram, what kind of plate boundary is present between points A and C? Divergent 17) In the Q14 diagram, what kind of plate boundary is present between points C and D? Convergent 18) Draw a cross-section using the figure in question 14 from A to D. Label oceanic crust and lithosphere, continental crust and volcanoes. What happens to the oceanic lithosphere beneath the continental crust? Why are there volcanoes here? 5

From A-C it’s the oceanic lithosphere, it goes underneath the continental crust From C-D it’s the continental crust , the oceanic crust creates more materal making the lithosphere afloat From B-D is volcanos , mostly underwater from pushing hot air up 19) Discuss why plate motion rates might be different between the Juan de Fuca (Q14) and the Mid-Atlantic Ridge (Q12)? What does this tell us about the potential driving mechanisms of plate Tectonics? Based on the creation of the oceanic crust which could go on top of the continental crust to create more 6

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