GEOL 285 12/6/2005 Dr. Lang 1 Study Guide for GEOL 285 - Petrology Final Exam – Fall 2005 The exam will be held at 8-10 am, Wednesday, Dec. 14, 2005 in Room 310, White Hall Dr. Lang will be available to answer questions on Monday, Dec. 12, and Tuesday, Dec. 13, at most times between 10am and 5pm (except lunchtime) in 308 White Hall. Questions on the final will be selected from the subjects and content of these questions. However, questions on the final will be more specific and will refer to specific diagrams that you will be given (like other tests). They won’t match these questions exactly. Comprehensive (Review) Questions on Igneous Rocks 1. Given the Streckeisen (QAPF) diagram for naming igneous rocks, how do you plot and name a plutonic igneous rock with a given percentage of plagioclase, quartz, alkali feldspar, orthoclase, feldspathoid, hornblende, pyroxene, biotite, etc.? 2. The box on the right of the QAPF diagram near P=plagioclase contains the three names: diorite, gabbro, and anorthosite. What are the two mineralogical characteristics that allow you to give the correct name to a rock that plots in that box, and what do they mean? 3. Be able to completely describe the equilibrium crystallization of any liquid on the Diopside-Anorthite, Forsterite-Enstatite-SiO2, or the Albite-Anorthite phase diagram (discussed in class). At any temperature, be able to say what phases would be present, and tell the composition and proportion (amount) of each. Questions on the characteristics and generation of subduction-related andesitic magmas at convergent margins (not covered on Midterm exam) 4. What are three characteristics (describe each in detail) of subduction-related magmas (like the Cascades) that must be explained by any good model for generation of those magmas? 5. What is bimodal volcanism, and what may happen in a shallow magma chamber to cause it? 6. Describe in detail the zoned ash flows exposed at the Pinnacles in the river valley south of Crater Lake. What is thought to have happened in the shallow magma chamber beneath Mount Mazama to cause those zoned ash flows? 7. According to J.K. Gill’s model (presented in class) for the generation of subduction related andesites, magmas produced above a subducting slab typically get trapped in a magma chamber at the base of the continental crust. Why do they get trapped?GEOL 285 12/6/2005 Dr. Lang 2 8. What happens in the magma chamber that allows the magma to rise and gives it the characteristics described in Question 4, above? (Critical element of Gill’s model, be specific) Questions on Dr. Penny L. King’s talk on Volatiles in Magmas (Friday before Thanksgiving, see link to talk on 285 class Web-site) 9. Discuss in detail one of the reasons presented by Dr. King for why we, as geologists, should care about the volatiles in magmas. Weathering, sediments and Sedimentary Rocks 10. What are the two main aspects of weathering? Which is most important for the eventual breakdown of rocks? 11. What unusual properties of water contribute to each of the above aspects of weathering? (Be able to discuss.) 12. What is Goldich’s Weathering Series and why does it resemble Bowen’s reaction series? 13. What minerals or groups of minerals do all silicate minerals weather to form? What happens to iron that weathers out of silicate minerals? 14. Grain size is an important characteristic of detrital or clastic sedimentary rocks. What is the Phi(ø)-scale? What equation relates the size in millimeters to a corresponding phi size? 15. How would you determine the range in phi-sizes of grains from a given sample of loose sediment? What tools would you need to do this accurately? How would you determine the range in phi-sizes of grains from a sample of lithified sandstone? What tools would you need for this? 16. Clay minerals in sedimentary rocks can be either detrital or authigenic. What is meant by each of these terms, and how can you tell if the clay in a particular rock is detrital or authigenic. 17. What is meant by sorting, rounding, sphericity as they apply to sand grains? What might these characteristics tell you about the history of a sandstone? 18. What are the three most common sand-sized grain types in sandstone? 19. On the Folk sandstone classification diagram used in class, what grain types are at the corners of the front triangle used for naming Arenites? Given the diagram, you should be able to plot and name any arenite.GEOL 285 12/6/2005 Dr. Lang 3 20. What is the maximum amount of detrital clay (mud) that a sandstone can contain, and still be classified as an arenite? 21. What are the abundant grain types in a litharenite? What are the abundant grain types in an arkose? 22. Does a lithic arkose contain more or less feldspar than a feldspathic litharenite? 23. What are the sandstones that contain between 15% and 50% mud matrix called, as a group? What are the three possible names of sandstones in this group, and what are the major sand grain types in each? 24. What is meant by the concept of textural maturity as it is applied to sandstones? What characteristics (and direction of change) of a sandstone indicate increasing textural maturity? 25. What are the characteristic properties, rock name, grain types, etc., of a supermature sandstone? 26. What are the characteristic properties, rock name, grain types, etc., of an extremely immature sandstone? 27. What might the textural maturity of a sandstone tell you about the transport, source area, depositional area and other aspects of the history of a sandstone? 28. What is meant by diagenesis, and under what conditions does it take place? 29. What are the two most important processes in the diagenesis of sandstones, and which is most important for the lithification of sandstones? 30. What are the four most common types of cements in sandstones? What can you say about the conditions in the solutions that passed through the sandstones that precipitated each cement (composition of solution, pH (acidity of solution), oxidation state of solution, etc.)? 31. Which cement is most soluble, and how does that affect its relative permanence in sandstones? Limestones 32. Which of the common carbonate minerals are polymorphs? What is their chemical formula? Which one is most stable at the Earth’s surface? Is it true that some organisms make their hard parts out of