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Metamorphism GLG 101 - Physical Geology Bob Leighty These notes and web links are your primary “lecture” content in this class. Additionally, various articles are assigned each week to supplement this “lecture” information. I believe you’ll have enough information to reference without having to purchase a costly textbook. These lecture notes are very similar to the ones I use in my traditional classes. You’ll find they are loaded with imagery and streamlined text that highlight the most essential terms and concepts. The notes provide a framework for learning and, by themselves, are not meant to be a comprehensive source of information. To take advantage of the global knowledge base known as the Internet, I have included numerous hyperlinks to external web sites (like the Wikipedia, USGS, NASA, etc.). Follow the links and scan them for relevant info. The information from linked web sites is meant to supplement and reinforce the lecture notes – you won’t be responsible for knowing everything contained in them. As a distance learning student, you need to explore and understand the content more independently than in a traditional class. As always, I will help guide you through this learning adventure. Remember, email Dr. Bob if you have any questions about today’s lecture ([email protected]). Leave no questions behind! Explore and have fun! Metamorphism Metamorphism Basics Changing pressure (P), temperature (T), and/or fluids cause original composition (mudstone) > new, more stable one (slate) without melting New minerals (e.g., garnet) may grow Any rock can be changed (metamorphosed) mudstone schist Metamorphism Metamorphism Basics Metamorphic grade – Describes intensity of P, T, & fluid activity Metamorphism Controlling Factors Temperature Sources of heat: > burial > subduction > nearby intrusions (magmas) Metamorphism Controlling Factors Pressure Confining Pressure - equal stress in all directions (lithostatic or hydrostatic) yields The arrangement of grains in a rock stays the same This stress creates nonlayered (nonfoliated) rock textures Metamorphism Controlling Factors Pressure Directed Pressure - tectonic stress The arrangement of platy minerals (if any) becomes more aligned This stress creates layered (foliated) rock textures Metamorphism Controlling Factors Fluids (mostly water) Sources of fluids: > forced out by pressure during burial > driven out of a magma during cooling & crystallization > driven out of a subducting tectonic plate Metamorphism Index Minerals Index minerals record the metamorphic grade The type of index mineral depends on P, T, & composition of rock being metamorphosed low grade mudstone high grade garnet schist high grade Metamorphism Types of Metamorphism Metamorphism Types of Metamorphism lo P & hi T hi P & hi T Metamorphism Types of Metamorphism Burial (diagenesis) (low P & low T) Increasing P & T during progressive burial Metamorphism Types of Metamorphism Contact (low P & variable T) Typically occurs near intrusions (batholiths, dikes, sills, etc.) The bigger the intrusion, the bigger the contact zone Metamorphism Types of Metamorphism Contact (low P & variable T) Creates nonfoliated metamorphic rocks (quartzite, marble, etc.) Metamorphism Types of Metamorphism Hydrothermal (low P & variable T & fluids) Movement of hot fluids (mostly water) > near magmas during crystallization > at hot springs and deep-sea “black smokers” Metamorphism Types of Metamorphism Regional (variable P & T) Affects large areas (100's to 1000's km2), typically in the lower crust Elevated P & T during mountain-building at convergent margins Metamorphism Types of Metamorphism Regional (variable P & T) Directed pressures may create foliated rock textures (slate, phyllite, schist, gneiss, etc.) Metamorphism Types of Metamorphism Cataclastic (dynamic) (localized high P & T) Crushing & shearing related to fault zones Creates foliated rocks (mylonites) Metamorphism Types of Metamorphism Impact (ultra-high P & T) Meteorite impacts melt & shatter rocks (yielding breccia & glass) Metamorphism WWW Links in this Lecture > Metamorphism - http://en.wikipedia.org/wiki/Metamorphism > Metamorphic grade - http://en.wikipedia.org/wiki/Metamorphism#Metamorphic_grades > Index mineral - http://en.wikipedia.org/wiki/Index_mineral > Foliation - http://en.wikipedia.org/wiki/Foliation_%28geology%29 > Diagenesis - http://en.wikipedia.org/wiki/Diagenesis > Contact metamorphism - http://en.wikipedia.org/wiki/Metamorphism#Contact_.28Thermal.29_metamorphism > Intrusion - http://en.wikipedia.org/wiki/Intrusion_%28geology%29 > Quartzite - http://en.wikipedia.org/wiki/Quartzite > Marble - http://en.wikipedia.org/wiki/Marble > Hydrothermal metamorphism - http://en.wikipedia.org/wiki/Metamorphism#Hydrothermal_metamorphism > Regional metamorphism - http://en.wikipedia.org/wiki/Metamorphism#Regional_metamorphism > Slate - http://en.wikipedia.org/wiki/Slate > Phyllite - http://en.wikipedia.org/wiki/Phyllite > Schist - http://en.wikipedia.org/wiki/Schist > Gneiss - http://en.wikipedia.org/wiki/Gneiss > Cataclastic metamorphism - http://en.wikipedia.org/wiki/Metamorphism#Dynamic_metamorphism > Mylonite - http://en.wikipedia.org/wiki/Mylonite