UB GLY 206 - Intro to Metamorph (7 pages)

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Intro to Metamorph



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Intro to Metamorph

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Pages:
7
School:
University at Buffalo, The State University of New York
Course:
Gly 206 - Geological Mapping Techniques and Communication

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Chemical Systems Introduction to Metamorphism Reading Winter Chapter 21 Definition of Metamorphism Metamorphism is a subsolidus process leading to changes in mineralogy and or texture for example grain size and often in chemical composition in a rock These changes are due to physical and or chemical conditions that differ from those normally occurring at the surface of planets and in zones of cementation and diagenesis below this surface They may coexist with partial melting Upper Limit of Metamorphism High temperature limit grades into melting Over the melting range solids and liquids coexist If we heat a metamorphic rock until it melts at what point in the melting process does it become igneous Xenoliths restites and other enclaves are considered part of the igneous realm because melt is dominant Migmatites mixed rocks are gradational An assemblage of coexisting phases thermodynamic equilibrium and the phase rule A basaltic composition can be either Melt Cpx plag olivine ilmenite Or any combination of melt minerals along the liquid line of descent If uplifted and eroded surface will weather a combinations of clays oxides Lower Limit of Metamorphism Low temperature limit Grades into diagenesis The boundary is somewhat arbitrary Diagenetic weathering processes are indistinguishable from metamorphic Metamorphism begins in the range of 100150oC for the more unstable types of protolith Some zeolites are considered diagenetic and others metamorphic pretty arbitrary Metamorphic Agents and Changes Temperature typically the most important factor in metamorphism Estimated ranges of oceanic and continental steady state geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface After Sclater et al 1980 Earth Rev Geophys Space Sci 18 269 311 1 Increased Temperature Promotes recrystallization which increases grain size Larger surface volume ratio of a mineral has lower stability High Temperature Effects Reactions occur that consume



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