111-29 - GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111...

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GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111 Lecture Notes Intro to Metamorphism Lecture Goals : A) Agents of Metamorphism B) Types of metamorphism C) Hydrothermal fluids Reference: Press et al., 2004, Chapter 9; Grotzinger et al., 2007, Chapter 6 A) Agents of Metamorphism The term metamorphism means to change a rock (commonly called the parent rock ) from its original composition (e.g., a shale or a basalt) to something new (e.g., a metamorphic rock). The cause of these changes are the so called "agents of metamorphism." The first time that I heard the term "Agents of Metamorphism", I thought it would make a great name for a punk rock band 1 . Now I know better; the AOM is a better name for a classic rock group. Bad music not withstanding, there are three true agents of metamorphism: 1. Heat (25˚C to 800˚C; up to the point of melting) 2. Pressure (1 Bar to 12,000 Bars) 3. Chemically active fluids 2 (AKA hot water) Each can single-handedly induce metamorphism in rocks, or they can act collectively. Heat is associated with one of two tectonic situations. The first is with proximity to intrusions like plutons, batholiths or laccoliths. The country rock that is in direct contact with these hot bodies experiences the highest temperatures. The further away that you get from the pluton, the lower the temperature. In this tectonic setting, the highest grade heat-only (or thermal) metamorphism is in direct contact with the intrusion. Lower grade heat-only metamorphism occurs further into the country rock. Areas of equal temperature that surround the intrusion are called isotherms and they more or less delineate the extent of heat-only metamorphism within the country rock. Because this type of metamorphism only occurs in contact with intrusions, it is usually called contact metamorphism . Good 1 The band that we had in my geology class was actually called Johnny Oolite and the Void Spaces. True story. Most geology classes have a "band" and most geology bands have geologically-inspired names. Like most university groups, Johnny and the boys kind of sucked. 2 Another great name for a rock band.
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GY 111 Lecture Notes D. Haywick (2008-09) 2 name huh? The area of metamorphism around the intrusion is frequently called a contact metamorphic aureole . The other tectonic setting where heat can induce metamorphic changes is through
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111-29 - GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111...

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