GEOL 106 - Assignment 1 - Plate Motion Winter 2020 PDF

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GEOL 106 Assignment 1 Winter 2020 – Plate Motion The speed at which tectonic plates move can be calculated in several ways. Satellite (remote sensing) technology allows us to determine precise distances and changes in distances on extremely fine scales letting us track current plate movements for most areas of the globe. There are other methods that can also be used. 1.

The record of magnetic field reversals in oceanic lava flows can be converted to a time clock by matching the pattern of magnetic changes in these rocks with the same pattern (radiometrically dated) in basaltic rock at midocean ridges. By using magnetometers on ships, the magnetic record on the seafloor can be determined from simple shipboard measurements. By knowing times and distances, how fast the seafloor has spread away from divergent plate boundaries can be calculated

2. Another major means of calculating plate velocities is tracking the volcanic "footprints" of hot spots as tectonic plates move across them. It is assumed that a hot spot originates from a relatively stationary source deep within the Earth's mantle. As plates move, these deep-seated plumes “burn" new spots on the plates. These spots might be volcanic islands in the ocean or volcanic features (such as geysers and hot springs) on continents. The hot mantle plume is like a lit match. Hold a piece of paper over it and it will begin to burn a hole in that paper. Move the paper slowly and the match will burn a series of holes in the paper, the oldest burnt hole being the one farthest away from the match. The age of the burns and their distance from the match can tell us how fast the paper has moved over it. P.S. DON'T TRY THIS AT HOME. The Hawaiian Islands, the Galapagos Islands and Yellowstone National Park are examples of hot spots. In this activity you will use readily available information for each of these areas of geologic interest in order to estimate how fast tectonic plates have moved over a time period of millions of years.

Part I: Hawaiian Islands Hot Spot While visiting Hawaii in the 1960's, J. Tuzo Wilson, noticed some interesting features about ocean islands. On a map of the Pacific basin, he found three linear chains of volcanoes and submarine volcanoes (seamounts). As shown to the right, these are the: 1) Hawaiian Islands - Emperor Seamounts; 2) the Pitcairn Island -Tuamotu Group; and 3) the Macdonald Seamount- Austral Group. Notice that the eastern most island or seamount of each chain is volcanically active. Of the three, the Hawaii - Emperor seamount chain is the most well-known. Wilson reviewed reports that had been published on these island chains and recorded the age of each island in the Hawaiian chain. An interesting pattern emerged; the islands become progressively younger to the southeast (lower right corner). Active volcanoes marked the extreme southeast end. This is true for all 3 chains.

GEOL 106 Assignment 1 Winter 2020 – Plate Motion Wilson proposed that the Hawaiian Islands formed successively over a common source of magma called a hot spot. The island of Hawaii is currently located above the hot spot. Hot, solid rock rises towards the hot spot from great depths (see left). Due to lower pressure at the shallower depth, the rock begins to melt, forming magma. The magma rises through the Pacific Plate to supply the active volcanoes. The older islands were once located above the stationary hot spot but were carried away as the Pacific Plate drifted to the northwest

**Questions are shown below, but you are given a separate answer sheet to submit.**

Part 1: Hawaiian Islands Hot Spot Using the map below (age of islands) as well as the provided distances to determine the rate of motion of the Pacific Plate over the Hawaiian hot spot. Rate is the distance traveled over a period of time. The distance traveled is equal to the distance from the present location of the hotspot (southeast Hawaii) to Ni’ihau. Time is the age of the island. So, to determine rate use: rate = distance/time.

Distance from Hawaii (current location of hot spot) to Ni’ihau = 540 km. Distance from Hawaii (current location of hot spot) to O’ahu = 330 km.

Note that Ma is an abbreviation for millions of years.

1A. To determine the average rate of motion for the Pacific Plate, divide the distance to Ni’ihau by the age of the island (Ni’ihau). The rate of plate movement is __ km/Ma (kilometres per millions of years). 1B. Convert your answer to cm/yr (centimetres per year). The rate of Pacific Plate movement is __ cm/year. Yikes – I forgot how to convert. Visit https://serc.carleton.edu/mathyouneed/units/index.html 1C. Using this rate, how far will the Pacific Plate move in 50 years? 1D. Repeat the exercise above using the island of O’ahu instead. From the distance and age of this island, the rate of Pacific Plate movement is __ cm/year

GEOL 106 Assignment 1 Winter 2020 – Plate Motion The Hawaiian Islands are part of a much larger chain of islands known as the Hawaiian-Emperor Seamount Chain (image on right). It consists of a series of seamounts (submerged volcanoes) and volcanic islands; which range in age from 0 Ma (Hawaii) to 81 Ma (Detroit seamount) 1E. Based on this image, has there been a change in the movement of the Pacific Plate over the past 80 Ma? Answer yes or no.

(from Torsvik et al., 2017; Nature Communications 8)

Part 2: Galapagos Islands The Galapagos Islands are part of another volcanic island chain formed as a plate travels over a hot spot. Using the provided maps, locate the tectonic plate that the Galapagos Islands are found on. 2A. What tectonic plate are the Galapagos Islands located on? 2B. What is the direction of motion (east, west, north or south) of this plate at the location of the Galapagos Islands?

Find the islands of San Cristobal and Fernandina on a map of the Galapagos Islands.

2C. Knowing the direction of plate movement, which of these two islands is younger and which is older? The plate tectonic story of the Galapagos is presented in the following article excerpt. Using information found in this article, you can calculate the rate of movement for the plate that the Galapagos ‘sits’ on. (Hint – make sure you read the first and last paragraphs)

GEOL 106 Assignment 1 Winter 2020 – Plate Motion

Plate Tectonics and the Formation of the Galapagos Islands by Dr. Robert Rothman The Galápagos are located on the very northern edge of the Nazca plate, which is bounded by the Cocos (north), the Pacific (west), the South American (east), and the Antarctic (south) plates (see maps). The Nazca plate itself is currently drifting south, away from the Cocos plate, and east, away from the Pacific plate. Since the net direction of drift is southeast, the Nazca plate is colliding with the South American plate. At the point of collision, the South American plate, which is made of light continental crust, is riding up over the Nazca plate, which is made of dense oceanic crust. This type of plate interaction is called subduction. As the Nazca plate is forced into the mantle, it melts, and its melt products work their way up to the surface to form volcanoes. The land is further raised by the crumpling effect as the western edge of the continent rides up over the descending plate. The result of all of this is the Andes, a young, highly volcanic, rapidly growing mountain chain. This same movement of the Nazca plate is responsible for producing the cluster of volcanic islands we call Galápagos. There is a large body of geophysical evidence for the existence of enormous plumes of hot mantle material that originate near the earth's core and rise all the way to the crust. These plumes seem to be stable over many millions of years. and with time, they burn through the crust to form an underwater volcano which may eventually grow big enough to become an island. But, because the crustal plate is in constant motion, the island will eventually move off of the hot spot. thereby making room for a second volcanic island. And a third, and a fourth.... Thus, are archipelagos like the Galápagos formed. Islands farthest from the hot spot are older and more eroded while islands near or on the hot spot are younger and steeper. Thus, Isla San Cristóbal, the nearest to the mainland, is approximately four million years old and composed of eroded, rounded cones, while Isla Fernandina dates at less than 7000 years and is considered to be one of the most active volcanoes in the world. Recently former Galápagos islands, now submerged, have been discovered between Isla San Cristóbal and the mainland. This discovery may double the age of the islands. Indeed, several million years from now the present islands may likewise sink beneath the waves only to be replaced by a new set of Galápagos Islands. Who can imagine what course further evolution will take?

2D. The ages of the islands of San Cristobal and Fernandina are ___ and ___. 2E. The distance between these two islands is 240 km, using this information, how fast is the plate moving (in cm/year)?

Part 3: Yellowstone National Park Hot spots may occur under continents as well. For example, one is located under the Yellowstone Caldera (Yellowstone National Park is located within it). A caldera is a volcanic feature formed by the collapse of volcano into itself, usually triggered by the emptying of a magma chamber beneath the volcano. It typically forms a large, bowl-shaped depression. The last eruption believed to have emptied the magma chamber beneath Yellowstone was ~ 630,000 years ago. It was the latest in a series of major caldera-forming eruptions that have occurred across the western United States during the last 16 million years. In fact, you can track the movement of this still active volcanic hot spot as it has shifted from southeastern Oregon (McDermitt Caldera) through Idaho into Wyoming. Check out the images below to view this track. In actuality, the hot spot is stationary. It is the North American plate that is moving across it. How fast is the plate moving? Apply the same method as before in order to calculate this rate. You will do this using the 12.5 Ma BruneauJarbridge Caldera in southern Idaho. The distance from this caldera to the Yellowstone Caldera is 485 km.

GEOL 106 Assignment 1 Winter 2020 – Plate Motion

3A. How fast is the North American plate moving? Give your answer in cm/year. 3B. Is the North American plate moving to the northeast or the southwest?...