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Arizona State University *
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Course
101
Subject
Geology
Date
Apr 3, 2024
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1
Uploaded by CountHedgehog2526
Lab 5: Igneous Rocks NAME Materials: Rock Kit, Computer with Google Earth Igneous rocks form in many different settings. They can form when magma cools underground, when lava cools at the surface, or when volcanoes violently erupt. These different settings produce igneous rocks with varying textures. Magma/lava composition controls on the style of eruption (effusive vs explosive) and the color of crystalline igneous rocks. The lab below provides practice in interpreting these textures and colors and connecting them to specific igneous environments. First, we start with igneous environments. .. Exercise 1. Magma Formation and Igneous Environments How does magma form? There are three mechanisms that can produce molten rock. All occur in the subsurface where rock material can reach temperatures above the melting temperature for rocks. Here are the mechanisms (see slides 9-16 for examples): e addition of heat — this occurs when there are hot spots in the mantle, typically far from plate boundaries e decrease in pressure — this occurs where crust is thinned out by divergent activity e addition of volatiles — this occurs where subduction carries CO; and H>O to the asthenosphere For the questions below you’ll need to use Google Earth. Here are instructions: = First download the required file (5_Igneous Rocks.kmz) from the course Canvas page (Files>Lab Materials). = Open Google Earth, then click Open>File and navigate to the 5_Igneous Rocks.kmz file you just downloaded. = Click to open the file. Questions (see slide 8 for examples of plate tectonic settings): a) Check and double-click on Ex1_placemark A, which should fly you to a trench off the coast of Japan. What is the cause of melting at this setting? b) Check and double-click on Ex1 placemark B, which should fly you to a feature in the middle of the Atlantic Ocean. What is the cause of melting at this setting? ¢) Check and double-click on Ex1 placemark C, which should fly you to the Canary Islands off the western coast of Africa. What is the cause of melting at this setting? d) Check and double-click on Ex1_placemark D, which should fly you to the Red Sea. What is the cause of melting at this setting? Exercise 2. Magma and Igneous Rock Composition Igneous rock composition is controlled by the composition of the magma/lava from which it formed. Magma composition, in turn, is controlled by numerous factors. Here we will consider how magma source and magma mixing control composition. Magma composition is defined by how much silica (Si0z), iron (Fe) and magnesium (Mg) it contains. Here are the terms we will use and some basics: Table 1. Igneous Rock Compositions
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