ENV 305 Online - Week 2 Assignment

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Wilmington University *

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305

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Geology

Date

Jun 13, 2024

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docx

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3

Uploaded by Anna100112

ENV 305 Online – Week 2 Assignment Page 90 question 3: Is it possible for two igneous rocks to have the same mineral composition, but be different rocks? Support your answer with an example. Igneous rocks form as magma cools and crystalizes and solidifies. It is possible for two igneous rocks to have the same mineral composition and be different rocks. Some examples are how volcanoes can make pumice and volcanic ash. Two other rocks that have the same mineral composition of pyroxene, plagioclase, and feldspar are basalt and gabbro, which are basaltic rocks. Common granitic rocks with the same composition are granite, rhyolite, and obsidian. Page 90 question 6: If you hiked to a mountain peak and found limestone at the top, what would that indicate about the likely geologic history of the rock there? Finding limestone at the top of a mountain peak is likely because this mountain was submerged in water at one point in time. Also, Limestone is an abundant sedimentary rock and is composed chiefly of the mineral calcite (CaCO 3 ). Limestone is the result of biochemical sediments produced by marine organisms. So, this can be caused by the precipitation of calcium carbonate from ocean water. Page 90 question 10 (a-d): Examine the accompanying photos, which show the geology of the Grand Canyon. Notice that most of the walls of the canyon consist of layers of sedimentary rocks, but if you were to hike down into what is known as the Inner Gorge, you would encounter the Vishnu Schist, which is a metamorphic rock. a. What process might have been responsible for the formation of the Vishnu Schist? How does this process differ from the processes that formed the sedimentary rocks that are atop the Vishnu Schist? b. What does the Vishnu Schist tell you about the history of the Grand Canyon prior to the formation of the canyon itself? c. Why is the Vishnu Schist visible at earth’s surface? d. Is it likely that rocks similar to the Vishnu Schist exist elsewhere but are not exposed at earth’s surface? Explain.
a. Vishnu Schist is a metamorphic rock that was formed from a previous sedimentary rock. Metamorphism had to have taken place because of high temperature and pressure within earth that changes the texture and mineral composition. “Most metamorphic changes occur at the elevated temperatures and pressures that exist in the zone beginning a few kilometers below the Earth’s surface and extending into the mantle” (Tarbuck & Lutgens, 2018) . This process differs from the processes that formed the sedimentary rocks that are atop the Vishnu Schist because t he metamorphic process forced plate tectonics to compress and bury rocks miles deep into the crust, whereas; the sedimentary process produces layers that are a mixture of soft and tough rocks. Sedimentary rocks form from a weathering process where pre-existing rocks are deposited, transported, and lithified. Piles of sediment accumulate over time and all the materials at the bottom are compacted over time by the weight of the overlying layers. b. 1. Deposition of sedimentary layers found above Vishnu Schist. 2. The formation of Vishnu Schist. 3. The carving of the canyon by the Colorado River 4. Its long history shows that the region underwent extensive metamorphism and geological activity. c. The Vishnu schist was exposed by geological processes and primarily when sedimentary layers above it were eroded. d. Yes, it is likely that there are similar rocks, but they aren’t exposed because they are under the earth’s surface. These similar rocks may be covered beneath other rocks or may have had insufficient amounts of heat and pressure within Earth’s surface and those sedimentary rocks are eroding in a much slower rate.
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