Lab 3 Global Plate Tectonics_spring 2024

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Apr 3, 2024

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100 points total Laboratory 3: Global Plate Tectonics Before Attending Lab This Week... ...read this introductory material. Purpose of This Lab In this lab we will investigate the global occurrence of volcanoes, earthquakes, topography, and oceanic crust age to further study plate tectonics. Plate tectonics and density In the 1st lab, we looked at densities of both individual minerals as well as dominant rocks in the continent, ocean, and mantle. Higher density minerals (e.g. olivine, perovskite, and spinel) as well as higher-density rocks (e.g. gabbro and dunite) contain higher amounts of magnesium and iron. This density difference also affects the interaction between continental and oceanic plates. Convergent boundaries In convergent plate boundaries, the plates are moving towards each other, resulting in the destruction of crustal material. The specific features present depend on the composition of the two plates. At convergent boundaries with an oceanic plate and a continental plate (e.g. Nazca plate and South American plate), the oceanic plate will subduct under the continental plate. This type of boundary has a trench , a deep canyon in the ocean floor formed by the down-going plate, and a chain of volcanoes called a volcanic arc. All of the world's largest earthquakes have occurred along this type of boundary; earthquake depths increase along the down-going plate. If both plates at a convergent boundary are oceanic (e.g. the Pacific Plate and the Philippine Plate), the chain of volcanic islands is called an island arc. Trenches and deep earthquakes are also present at this type of boundary. The deepest trench in the world is the Marianna Trench, which occurs where the Pacific and Philippine plate meet. If both plates are continental, with approximately the same density, neither plate subducts but instead collide and form mountain belts with thick continental crust (up to 70 km). Very few earthquakes or volcanoes tend to occur at these types of boundaries. The Himalayan and Appalachian Mountains are an example of this type of boundary . Divergent Boundaries At divergent plate boundaries, the two plates are moving away from each other, resulting in the creation of new ocean crust. Magma rises up from the mantle as the plates push away from each other, carrying the newly created ocean crust. At divergent boundaries between two oceanic plates, features present include underwater mountain ranges such as the Mid-Atlantic Ridge and volcanoes. Earthquakes tend to be very shallow (< 100 kilometers in depth) and fairly small in size (M < 5). Oceanic crust age increases away from the margin. Lab 3: Global Plate Tectonics 3-1

. Oceanic-oceanic divergence. Transform Boundaries At transform boundaries , crust is predominantly conserved as the plates slide past each other. These boundaries typically have no volcanoes, but instead produce strike-slip faults like the San Andreas. Terms to know Convergent Plate Boundaries Trench Volcanic Arc Island Arc Divergent Plate Boundaries Transform Boundaries References Turcotte, D. L., and Schubert, G., Geodynamics, New York, 1982 www.usgs.gov Hot Spots Not all geologic features are located along plate margins. Hot spots are volcanic areas in the crust fed by a rising plume of mantle material; they tend to be located away from plate boundaries. In the United States, Hawaii is a hot spot that occurs on an oceanic plate while Yellowstone is a continental hot spot. Hot spots commonly have shallow earthquakes and sometimes explosive volcanic eruptions (e.g. Yellowstone). Lab 3: Global Plate Tectonics 3- 2

ACTIVITY I. FEATURE MAPS At your table is a set of ONE of 4 maps in addition to the plate boundary map: Earthquakes, Volcanoes, Topography, and Age of the Oceanic crust. Please include the names of group members as appropriate below: GROUP 1 - EARTHQUAKES GROUP 2 - VOLCANOES GROUP 3 - TOPOGRAPHY GROUP 4 - AGE OF THE OCEANIC CRUST FOR THIS ACTIVITY, EACH GROUP SHOULD ANSWER THE QUESTIONS FOR ONLY THE MAP AT THEIR TABLE ( 4 points per question) GROUP 1- EARTHQUAKES: Earthquake magnitudes are indicated by the diameter of the circle, and earthquake depth is indicated by color. Red: Yellow: Green: 0 - 33 km depth 33 -100 km depth 100 - 400 km depth Blue: > 400 km depth 1) Do worldwide earthquakes always coincide with plate boundaries? If not, give a specific example (location, depth, and approximate number) where this is not present. Lab 3: Global Plate Tectonics 3- 3

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2) Discuss what happens to the depth of earthquakes along the western margin of the South American continent. What is the depth of the deepest recorded earthquake? Include whether there are any earthquakes with a magnitude > 8.6-9.0. What do you think this indicates about the type of plate boundary and which direction the two plates are moving? 3) Discuss the presence and depth of earthquakes along the boundary between the Australo- Indian and Eurasian plates. What is the depth of the deepest recorded earthquake? Include whether there are any earthquakes with a magnitude > 8.6-9.0. What do you think this indicates about the type of plate boundary and which direction the two plates are moving? Lab 3: Global Plate Tectonics 3- 4

GROUP 2 - VOLCANOES Historic eruptions (Eruptions since 4000 B.C.) are indicated by stars. Volcano types are indicated by color. Red - Calderas - craters formed from the collapse of a volcano that emptied its magma chamber. These volcanoes are among the most violent on earth. Green - Stratovolcanoes commonly found at ocean/continental boundaries, intermediate amounts of silica. May or may not be explosive. Blue - Shield volcanoes - commonly found at hot spots or ridges, low amounts of silica. Generally not explosive. Tan- Maars - craters formed when magma comes into contact with groundwater. Not common. 1) Do worldwide volcanoes always coincide with plate boundaries? If not, give a specific example (location, type, and any historic eruptions) where this is not present. 2) What type of volcano is present along the western coast of North America (intersection of the Juan de Fuca plate and the North American plate)? What type of plate boundary do you think this is, and what type of eruption would likely occur? Also include what type of igneous rock would likely be found here and the name of the specific volcano that erupted (indicated by star). Give reasons for your answers. 3) What type of volcano is dominant along the western coast of South America? What do you think this indicates about the type of plate boundary? Do you have an explanation for the two gaps in volcanoes along this margin? Give reasons for your answers. Lab 3: Global Plate Tectonics 3- 5

G ROUP 3 - TOPOGRAPHY Colors indicate height above the surface and ocean depths as follows: Oranges/browns: highest elevations (>5000 meters ~15,000 feet) Greens: sea level Deep pink/white: deepest depths (>7000 meters ~21000 feet) 1) Discuss the correlation of the shallowest depths (sea level) with the plate boundaries along the mid-ocean boundary in the Atlantic. What do you think this indicates about the type of plate boundary? Also include what type of igneous rock would likely be found here and your reasoning. 2) Discuss the feature along the boundary between the Pacific and the Philippine plate in terms of depth. What type of plate boundary do you think this is and what type of feature is present? Include the specific name if possible. 3) Discuss the area of high elevation at the boundary of the Australo-Indian plate and the Eurasian plate. What do you think this indicates about the type of plate boundary? Include the specific name of the feature if possible. Lab 3: Global Plate Tectonics 3- 6

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GROUP 4 - AGE OF THE OCEANIC CRUST Oceanic crust age is indicated by color: Red/orange: youngest crust (0-10 Million years) Light greens/blues: intermediate crust (70-90 Million years) Dark Blues: oldest crust (> 140 Million years) 1) How does the age of the ocean crust coincide with worldwide plate boundaries? Include in your answer one place (location and crustal age) where the oldest crust is found. 2) Discuss the age of the ocean crust on the western margin of South America (Nazca plate). How old is the oldest crust? What do you think this indicates about the type of plate boundary between the Nazca plate and the Pacific plate? 3) Discuss the age of the ocean crust at the boundary of the Australo-Indian plate and the Eurasian plate. Is there any ocean crust present? What do you think this indicates about the type of plate boundary and what happened? Lab 3: Global Plate Tectonics 3- 7

ACTIVITY II. PLATE TECTONICS JIGSAW One person from each group in activity I should join a different group, taking one of your initial maps with you. The new group should have AT LEAST one person from EACH of the previous groups. Please indicate the name of everyone at your table and which group they represent: EACH OF YOU HAVE NOW BECOME THE EXPERT FOR YOUR SPECIFIC MAP. DISCUSS THE FOLLOWING AS A WHOLE GROUP AND ANSWER THE FOLLOWING QUESTIONS: AUSTRALO-INDIAN PLATE AND EURASIAN PLATE For the Australo-Indian and Eurasian plate boundary, answer the following questions Discuss this plate boundary in detail. Include in your answer the type of plate for both Australo- Indian and Eurasian Pacific plates (oceanic or continental), the direction of motion, and type of boundary. Include any change in oceanic crust age across this region with specific ages, the presence/depth of earthquakes and any significant earthquakes, the presence and type of any volcanoes, and topography along the margin. Also include what type of rock you would find at this boundary and justify your answer (1 4 points). Lab 3: Global Plate Tectonics 3- 8

NORTH AMERICA AND PACIFIC PLATE For the North American and Pacific plate boundary (Alaska) , answer the following questions. Specifically, focus on the portion of the boundary at the northern edge of the Pacific Plate. Discuss this plate boundary in detail. Include in your answer the type of plate for both North America and Pacific plates (oceanic or continental), the direction of motion, and type of boundary. Include any change in oceanic crust age across this region with specific ages, the presence/depth of earthquakes and any significant earthquakes, the presence and type of any volcanoes, and topography along the margin. Also include what type of rock you would find at this boundary and justify your answer (1 4 points). PACIFIC PLATE AND ANTARCTIC PLATE For the Pacific Plate and the Antarctic Plate, answer the following questions. Specifically, focus on the portion of the boundary at the southeastern edge of the Pacific Plate. Discuss this plate boundary in detail. Include in your answer the type of plate for both the Antarctic and Pacific plates (oceanic or continental), the direction of motion, and type of boundary. Include any change in oceanic crust age across this region with specific ages, the presence/depth of earthquakes and any significant earthquakes, the presence and type of any volcanoes, and topography along the margin. Also include what type of rock you would find at this boundary and justify your answer (1 4 points). Lab 3: Global Plate Tectonics 3- 9

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FAILED RIFTS Failed rifts are areas on the Earth’s surface that did not lead to the formation of new ocean crust. They can often be identified by the presence of volcanoes, shallow earthquakes (< 33 km in depth), and may or may not occur along a plate boundary. Do you see any evidence on the maps for a failed rift? Discuss any locations in terms of the presence and depth of earthquakes, the presence and type of volcanoes, topography, plate boundaries, and any expected ocean crust ages (5 points) Discuss any reflections/comments on how you felt performing the jigsaw activity or the performance of your group ( 5 points). Lab 3: Global Plate Tectonics 3-1 0

Lab 3 Global Plate Tectonics_spring 2024

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