Geology 723--Igneous Petrology
Instructor: Sheila Seaman, Morrill 242; phone 545-2822; office hours: M,W 2-4; e-mail: sjs@geo.umass.edu
Text: Philpotts, A.R., Principles of Igneous and Metamorphic Petrology, Prentice-Hall Publishing Co., 1990
This course is designed to be a study of the phase equilibria and geochemical aspects of the formation of igneous rocks, within the context of a variety of Earth tectonic environments. The course will begin with a discussion of the generation of the most primitive kinds of magmas by melting of the mantle, and will progress from there, considering the physical and compositional conditions that lead to the remarkable and distinctive diversity of igneous rock provinces on the Earth. The ultimate goal of the course is to explore the range of computational techniques of modern igneous petrology, so that as researchers we can derive the maximum amount of information possible from suites of igneous rocks in the quest to understand their petrogenesis.
The textbook that has been chosen for the course deals with the principles used to study igneous rocks--properties of magmas, mechanisms of melt production and crystal formation, the effects of volatiles on magmatic processes, and thermodynamics and phase equilibrium. This textbook does not merely describe and classify the kinds of igneous rocks that occur in various tectonic settings. Its goal, and the goal of this course, is to teach petrologic principles, and to apply them within the peculiar sets of physical circumstances that nature produces.
The format of the course emphasizes lectures and problem-solving, but occasionally a class meeting will be devoted to discussion of a landmark journal paper or to topical discussion. Although there is no scheduled lab, I will provide occasional suites of rocks and thin sections and some questions for guidance as you view them. The basis for a grade in the course will be one take-home midterm and one take-home final exam, homework problem sets, and a semester-long research project. Some of the homework material will apply directly to the rock and thin section suites and associated questions, some will be calculation-style problems, some will be phase diagram manipulation problems, and some will be geochemically-oriented problems dealing with the evolution of magmas, mostly using the petrologic modeling program MELTS. Homework exercises should be done on time; they will loosely build on one another, so that it may be difficult to do a later one without having completed previous ones.
Finally, there will be one weekend field trip; we’ll plan this for a weekend when we’re all free (!).
Syllabus
Date Topic Reading
Jan. 29 The Mantle--Where igneous rocks come from Philpotts, Ch.1
31 Mantle characteristics Yoder, 44-88
Feb. 3 Mantle melting
5 Mantle melting
7 Basalts--Their classification and properties Morse, Ch.1,2
10 Basaltic phase equilibria--an overview Morse, Ch.3,4
Feb. 12 How to Make a Phase Diagram: First Law of Thermodynamics Philpotts, p. 103-110
14 Second and Third Laws Philpotts, p. 110-112
17 No Class--Presidents’ Day
19 Gibbs Equation and Free Energy of Formation Philpotts, p. 112-116
21 Free energy surfaces and plotting univariant lines Philpotts, p. 118-122
24 Free energy of solutions: ideal Philpotts, p. 134-139
26 Free energy of solutions: non-ideal Philpotts, p. 139-142
28 Exsolution Philpotts, p. 142-146
Mar. 3 Binary Phase diagrams--Di-An Morse, Ch 4,5; Philpotts 148-168
5 An-Ab
7 MORB Genesis and Evolution: ternary system Di-An-Ab Morse, Ch. 8
10 Fo-Di-An Morse, Ch. 9
12 Fo-An-Si Morse, Ch. 10
12 Fo-Di-Si Morse, Ch. 11
14 Pyroxene phase equilibria Morse, Ch.12
17-23 No Class--Spring Break
24 Layered mafic intrusions--Tectonics, phase petrology Morse, Ch.13
26 The dynamics of intrusion of magma bodies Philpotts, Ch.3
28 Thermal effects of intrusions on country rocks Philpotts, Ch.5
31 Island arcs--Generation of island arc magma suites
Apr. 2 Effects of volatiles on melt equilibrium Philpotts, Ch.11
4 Trace and rare earth element fractionation Cox, Pankhurst, and Bell, Ch.
7 Isotopic characterization of magma sources Cox, Pankhurst, and Bell, Ch.
9 The origin of andesites Grove and Kinzler paper
11 Active continental margins--Effect of continental crust on magma generation
14 The peculiarities of back-arc basins
16 Magmatic processes--Crystal settling, magma convection Philpotts. Ch.13
18 Diffusion, magma mingling and mixing
21 No Class--John Muir’s Birthday
23 Granites--Classification, phase petrology Tuttle and Bowen; Morse, Ch.15
25 Petrogenesis Whitney paper
28 Feldspar phase equilibrium Philpotts, 182-184
30 Explosive volcanism--Anecdotes
May 2 Mechanisms of eruption Philpotts, 19-23
5
7 Continental rift zones--Tectonics and classification Wilson, Ch.11
9 Implications of bimodal magmatism
12 Overview and catch-up
14 Overview and catch-up
No Class--Presidents' Day
24-26 Binary phase diagrams: Di-An, An-Ab Philpotts, 148-168; Morse, Ch.4,5
Mid-ocean ridges--Physics and chemistry
27 MORB evolution: the ternary systems Di-An-Ab, Morse, Ch.8, 9
Mar. 1-3 Fo-Di-An, Fo-An-Sil, Fo-Di-Sil Morse, Ch.10,11
6 Pyroxene phase equilibria Morse, Ch.12
8 Layered mafic intrusions--Tectonics, phase petrology Morse, Ch.13
10 The dynamics of intrusion of magma bodies Philpotts, Ch.3
13 Thermal effects of intrusions on country rocks Philpotts, Ch.5
15 Island arcs--Generation of island arc magma suites
17 Effects of volatiles on melt equilibria Philpotts, Ch.11
18-26Spring Break
27-29 Trace and rare earth element fractionation Cox, Pankhurst, and Bell, Ch.
31-Apr.3 Isotopic characterization of magma sources Cox, Pankhurst, and Bell, Ch.
Apr. 5-7 The origin of andesites Grove and Kinzler paper
10-12 Active continental margins--Effect of continental crust on magma generation
14No class
17No class
19 The peculiarities of back-arc basins
21 Magmatic processes--Crystal settling, magma convection, Philpotts. Ch.13
24 diffusion, magma mingling and mixing
26-28 Granites--Classification, phase petrology Tuttle and Bowen; Morse, Ch.15
May 1 Petrogenesis Whitney paper
3 Feldspar phase equilibrium Philpotts, 182-184
5 Explosive volcanism--Anecdotes
8 Mechanisms of eruption Philpotts, 19-23
10 Continental rift zones--Tectonics and classification Wilson, Ch.11
12 Implications of bimodal magmatism
15-17 Overview, summary, and
catch-up
Supplementary Texts and Papers
Cox, K.G., J.D. Bell, and R.J. Pankhurst, 1979. The Interpretation of the Igneous Rocks. London: Allen and Unwin.
Ehlers, Ernest G., 1972. The Interpretation of Geologic Phase Diagrams. San Francisco: W.H. Freeman and Co.
Maaloe, S. 1985. Principles of Igneous Petrology. Berlin: Springer-Verlag.
Grove, T. and R. Kinzler, 1986. Petrogenesis of andesites, Annual Review of Earth and Planetary Science. 14, 417-454.
O'Nions, R.K., 1987. Relationships between chemical and convective layering in the Earth. J. Geol. Soc. Lond. 144, 259-274.
Tuttle, O.F. and N.L. Bowen, 1958. Origin of granite in the light of experimental studies in the system NaAlSi3O8-KAlSi3O3-SiO2-H2O. Geol. Soc. Am. Memoir 74.
Whitney, J.A., 1988. The origin of granite: the role and source of water in the evolution of granitic magmas, Geol. Soc. Am. Bull. 100, 1886-1897.
Wilson, M., 1989. Igneous Petrogenesis. London: Allen and Unwin.
Yoder, H.S. Jr., 1976, Generation of Basaltic Magma, Washington D.C.: National Academy of Science