chapter8 - Key Terms and Concepts Definition of...

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Unformatted text preview: Key Terms and Concepts Definition of metamorphism, concept of equilibrium Agents of metamorphism: T, P, stress, fluids, strain Foliated vs. nonfoliated: Development of foliation (preferred orientation of grains) Degree of foliation (slate, phyllite, schist, gneiss) Introdution to principal stresses ( σ 1 , σ 2 , σ 3 ) Common nonfoliated rocks Types: related to geothermal gradient (PT diagrams) contact, hydrothermal, regional, burial, franciscan, fault zone, impact Metamorphic facies (stability of group of minerals) Metamorphism related to plate boundaries (What type(s) occur where?) What is metamorphism? ● Metamorphism » rock recrystallizes in the solid state (no melting) usually at T > 200ºC » Can change texture, mineralogy, and composition (if open system) » As with weathering, minerals will alter when subjected to conditions different from their origin » Seek to be in equilibrium with surroundings Agents of Metamorphism ● Temperature, pressure, stress, fluids, shear strain 100 200 300 500 1000 1500 Continent Ocean Temperature (°C) Depth (km) ● Temperature - increases with depth » Geothermal gradient - variable; 30ºC/km on continent Agents of Metamorphism (cont.) ● Temperature – Increased ductility and causes recrystallization ● Pressure & Stress » Confining pressure - equal in all directions » Differential stress - different values in different directions, may be caused by tectonic activity ( differential compression, shear, tension ) » ( σ 1 , σ 2 , σ 3 ) Confining pressure is like hydrostatic pressure....
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This note was uploaded on 03/27/2008 for the course GEOL 101 taught by Professor Olinsky during the Fall '08 term at Texas A&M.

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chapter8 - Key Terms and Concepts Definition of...

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