EARTH121 Chapter Notes - Chapter 7: Overburden Pressure, Metasomatism, Shear Stress
25 Aug 2016
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The type and degree of change of the parent rock depends on the intensity of the metamorphic process. Heat: drives the basic chemical reactions that changes composition (minerals transformed into new forms, influences mobility and reactivity of chemically active fluids, parent rocks can be heated in 2 different methods: Heat given off by intrusive bodies (plutons cooling) Happens at great depth, usually rocks that are forced under in subduction zones. Pressure (stress: heat is responsible for chemical changes whereas pressure is responsible for physical changes. Dictates distribution of elements within metamorphic rocks: confining pressure (uniform stress) Confines material into the smallest possible volume (shape does not change) Unequal application of stress resulting in the distortion of the body. Within earth"s crust (depth), this type of pressure horizontally stretches and compresses the rock and is caused by tectonic activity. Shear stress: forces are parallel but opposite directions: layers slide into each other.
