(30 point) Questions
1. Explain how magmas migrate from their locations of origin to their final emplacement within or on top of the crust of the Earth. Take into account the differences in temperature, pressure and composition of the magmas and their surrounding materials in your arguments.
2. Make a diagram of a typical island arc subduction zone. Label
all major features. Where is magma generated in such a system?
Why is it generated in those places? What controls the general chemical
character of the produced magmas? Use a K2O vs Si2O
diagram to illustrate your main points regarding magma generation and evolution.
What role does dehydration of the down going slab have in the generation
and composition of the magmas produced?
(20 point) questions
1. Describe the mechanism of basaltic underplating as it applies to the formation of flood basalts. Give an actual example to prove your argument.
2. Discuss the three mechanisms by which the mantle can undergo partial melting to produce basaltic magmas. Give examples of geological environments where each type is manifest.
3. Discuss the roles played by fractional crystallization and partial melting in producing either an alkalic series or a tholeiitic series of products. Use the Q-Ne-Ol triangular diagram to explain your answer.
4. Explain how a specific phase diagram would govern the melting of a rock of specific composition (e.g. using the system of olivine-SiO2 polymorph or another similar system with an eutectic or cotectic).
5. What is the general petrologic composition of the mantle and how
does it have a bearing on the production of magmas of different compositions?
(10 point) questions
1. Name some igneous rocks given their chemical composition and an appropriate diagram on which to plot the data.
2. What is the role of depth (pressure and source composition) and % melting on the formation of melts of tholeiitic, high-Al2O3, and alkalic compositions?
3. How can the Q-Ab-An triangular phase diagram be used to determine the water pressure and depth at which granites form?
4. How can a Harker-type diagram be used to show the effects of fractionation of olivine from a basaltic magma? The data at hand would be chemical analyses of major elements in basalts erupted at the surface. I will probably provide a diagram and ask some questions.
5. Determine the settling velocity of a mineral in a magma using Stoke's law. Determine how long it would take for the mineral to reach a certain depth specified by the exam question.
6. Define a few terms related to the genesis of igneous rocks, including the various elements of subduction zones related to petrogenesis and various features related to the mantle.
7. Explain the distinction between alkaline, calc-alkaline, and tholeiitic series using appropriate diagrams. You should be able to plot these series correctly on the diagrams.