Geology 591G
Granites and Rhyolites
Instructor: Sheila Seaman Office: 242 Morrill Phone: 5-2822
E-mail: sjs@geo.umass.edu Office hours: Tuesdays 11-1; Wednesdays 2-4
Textbooks: none that you have to purchase; readings will be assigned from the general literature and from the following reference books:
Johannes and Holtz, 1996, Petrogenesis and Experimental Petrology of Granitic Rocks, Springer-Verlag.
Proceedings of the Third and Fourth Hutton Symposia on the Origin of Granites and Related Rocks, Royal Society of Edinburgh
Course Description:
The purposes of this course are to explore the origin and significance of silicic magmas in terms of the existence and geologic evolution of Earth's continental crust, and to investigate the role of silicic magmatism in the fields of structural geology, materials science, planetary geology, and volcanic hazards. Topics that we will consider during the course include the generation of silicic magma in the lower crust and/or in the mantle, properties of silicic magmas, diffusion in silicic magmas, effect of volatiles on magma behavior, implications of rock fabric for magma genesis and evolution, modes and causes of eruption of granitic magma, styles of eruption, the significance of disequilibrium textures in granites and in rhyolites, means of emplacement of granitic plutons in relatively shallow crust, the geochemical association of granites with their source rocks and tectonic settings, and the planetary significance of silicic igneous rocks.
In general, I will present the topic of the week during the first class meeting each week, and will provide you with a few thin sections of samples relevant to the topic. During the second class meeting of the week, we will discuss a literature paper, provided on the previous Friday, and relevant to the topic of the week. A class member will present a summary of the journal paper each week. The verbal summary will be accompanied by a word-processed one-page condensed version of the paper, including a figure or two with captions in your own words.
During the third class meeting, we will discuss the thin sections.
Each person in the class will do a research project on a famous granite or rhyolite. This project will involve literature-based research on the tectonic setting and likely source material of the silicic magma, preparation of one or more thin sections, major and trace element analyses, fabric analyses in thin section and in hand sample, and electron microprobe analysis of minerals. Each person will write a research paper based on this experience, and will present the results of his or her work to the rest of the class during the last week of the semester.
One field trip, to Vinalhaven island, Maine, is scheduled for the course. We will leave UMass on a Saturday afternoon, will stay on the mainland Saturday night, and ride a ferry to the island on Sunday morning. We will spend the day on the island and return to Amherst Sunday evening. The dates of the field trip will be established during the first full week of the semester.
Granites and Rhyolites
Weekly Topics
September 8, 15 The classification and origins of granitic and rhyolitic magmas
September 22 Felsic magma chamber processes--gravity settling, thermogravitational diffusion, convection, and more
Sept. 29, Oct. 6 Rhyolitic volcanic processes--pyroclastic rocks and lava domes
October 13 Significance of volatiles in granitic magmas
October 20 Styles and significance of diffusion in granitic magmas
October 27 Using granite petrology to interpret source materials and genetic history: isotope geology of granitic magmas
November 3 Using granite petrology to interpret source materials and genetic history: trace and rare earth element geochemistry of granitic magmas
November 10 Ascent and emplacement of granitic magmas
November 17 Granitic magmatism and orogenesis
November 24 Silicic magmas in planetary perspective--terrestrial and extraterrestrial
December 1 Thermobarometry of granites and rhyolites
December 8 Presentation of final projects