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Geology 101 Name: Homework assignment 2 Due in class on by e-­‐mail Monday, October 12, 5 p.m. 1. Look at any plate tectonic map of the world (like the one in the text on pages 68 and 69), and find the Pacific Northwest. The Cascades mountain range has many active volcanoes (like Mt. St. Helens and Mt. Rainier), and the range extends from southern British Columbia to northern California. How can plate tectonic theory explain why there are no volcanoes north of Mt. Garibaldi in southern BC or south of Mt. Lassen in northern CA? 2. There are a lot of abandoned metal ore mines in the western Cascade mountains; for instance, silver and lead from the Monte Cristo area in Snohomish County and copper and silver from the Denny Creek area in King County. According to the text, what type of plate boundary do we live near, and how does this tectonic setting allow for the economic concentration of metals? 3. Ice is, of course, the solid crystalline form of water. Under the definition of “mineral” given in chapter 4, would ice be considered a mineral? Do a little searching on the Web; is there a consensus among various geology sites about whether ice is a mineral or not? 4. Is quartz a mineral or a rock or both? Explain your choice, using the definitions of mineral and rock given in chapter 4. 5. Is the mineral property “hardness” defined by how strong the mineral is? To put it another way, if you smash a diamond (Mohs scale hardness 10) with a hammer, are you demonstrating the diamond’s hardness or some other property of the diamond? If the latter, what property or properties listed in chapter 4 will you demonstrate? 6. In an ophiolite, ultramafic rocks are found at the base of the sequence and basalt is found at the top of the sequence, with gabbro found about midway. Explain how this distribution of rocks in an ophiolite is consistent with the composition and texture expected at different levels of the oceanic crust and upper mantle.