Petrology and Plate Tectonics
This course is organized around the igneous and metamorphic processes that govern the rock cycle, all within the context of plate tectonics. Rather than addressing igneous and metamorphic rocks and processes as though they are independent of each other, the course integrates their study into a harmonious whole. I begin with an overview of how plate tectonics and the water cycle make the Earth unique in the solar system, simultaneously introducing the intellectual underpinnings of Petrology: that we use rock texture and chemical composition, including mineral composition and distributions, to decipher tectonic history. I then follow Earth materials through a hypothetical rock cycle, from formation and metamorphism at the mid-ocean ridge, through subduction, plutonism, and contact metamorphism, to continental rifting and collision. It concludes with chapters on hotspot and LIP magmatism and on the production of fault rocks at transform fault boundaries. I am writing a textbook with the same organizational structure.
This is the sequence of course topics, and the underlying central concepts I emphasize with each topic:
- Plate tectonics and petrology. Central concept: The earth is fundamentally different from other planets in having active plate tectonics and a water cycle, and this is reflected in its igneous and metamorphic rocks.
- Formation of the Earth.
- Mid-ocean ridges: production of oceanic crust. Central concept: Rifting produces basaltic crust by melting during upwelling; water is fixed into this new lithosphere by metamorphic processes.
- Melting and crystallization in basaltic systems.
- Metamorphism and hydration of oceanic lithosphere. Central concept: Hydrated oceanic lithosphere undergoes a series of reactions that eventually release water, which triggers subduction-zone magmatism.
- Subduction and the generation of magma.
- Volcanism. Central concept: The wide range of magma compositions produced in subduction zones is reflected in diverse styles of volcanism.
- Causes of magmatic diversity. Central concept: Magmatic diversity can be produced by a wide range of processes that are governed by crystal-melt phase equilibria; trace element and isotope geochemistry can be used to test hypotheses about magmatic differentiation and to determine timescales of magmatism and metamorphism.
- Plutonism and batholiths. Central concept: Diverse processes can cause magma to freeze in the crust, producing plutons; silicic magmas can be generated by crustal melting.
- Contact metamorphism and geochronology. Central concept: Heat leaks from intruded magma through the host rocks, producing metamorphic reactions and controlling when isotopic clocks start.
- Continental rifts. Central concept: Stretching of continents can produce continental fragments along with voluminous magmatism that may be unusual in composition.
- Continental collision and metamorphism. Central concept: Subduction of continental fragments jams subduction zones, producing high mountains and regional metamorphism.
- Hot spot and LIP magmatism. Central concept: Focused magmatism can occur away from plate boundaries, perhaps in response to plumes welling up from the deeper mantle.
- Transform fault boundaries. Central concept: Sliding along transform margins produces fault rocks.
- Describe how the Earth's crust was constructed by igneous and metamorphic processes.
- Describe the plate tectonic settings of magmatism and metamorphism.
- Interpret tectonic setting from igneous and metamorphic rock assemblages.
- Identify and interpret igneous and metamorphic rocks in hand sample and thin section.
- Interpret geologic maps of igneous and metamorphic rocks.
- Observe, describe, sample, and analyze rocks in outcrop.
- Analyze rock genesis (e.g., P-T conditions; source materials) using mineralogy, texture, geochemistry, and isotopic data.
- Balance chemical reactions between minerals.
- Describe how a magma's physical properties affect its eruptive and intrusive behavior.
- Deduce by observation whether a volcano is likely to erupt and what kinds of eruptions it might produce.
- Analyze magma changes during melting and crystallization using phase diagrams.
- Predict changes in rock mineralogy with changes in P-T conditions using phase diagrams.
- Describe chemical exchanges between Earth's lithosphere and the atmosphere and hydrosphere.
- Use isotopic data to determine the age of crystallization or cooling of a rock.
How course activities and course structure help students achieve these goals: