GLG Physical Geology Bob Leighty Metamorphism These lecture notes are very similar to the ones I use in my traditional classes. Youll 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 wont 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,Dr. Bob if you have any questions about todays lecture Leave no questions behind! Explore and have fun! 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 youll have enough information to reference without having to purchase a costly textbook. 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 Basics Metamorphism Metamorphism Metamorphic grade Describes intensity of P, T, & fluid activity Metamorphic grade Sources of heat: >burial >subduction >nearby intrusions (magmas) Controlling Factors MetamorphismTemperature Confining Pressure - equal stress in all directions (lithostatic or hydrostatic) The arrangement of grains in a rock stays the same This stress creates nonlayered (nonfoliated) rock textures yields Controlling Factors MetamorphismPressure Directed Pressure - tectonic stress The arrangement of platy minerals (if any) becomes more aligned This stress creates layered (foliated) rock texturesfoliated Controlling Factors MetamorphismPressure > driven out of a magma during cooling & crystallization > forced out by pressure during burial > driven out of a subducting tectonic plate Controlling Factors Metamorphism Fluids (mostly water) Sources of fluids: mudstone garnet schist The type of index mineral depends on P, T, & composition of rock being metamorphosed low grade high grade Index minerals record the metamorphic grade Index minerals Index Minerals Metamorphism high grade Types of Metamorphism Metamorphism lo P & hi T hi P & hi T Types of Metamorphism Metamorphism Increasing P & T during progressive burial Types of Metamorphism Metamorphism Burial (diagenesis) (low P & low T) Types of Metamorphism Metamorphism Contact (low P & variable T) Typically occurs near intrusions (batholiths, dikes, sills, etc.)intrusions The bigger the intrusion, the bigger the contact zone Creates nonfoliated metamorphic rocks (quartzite, marble, etc.)quartzitemarble Types of Metamorphism Metamorphism Contact (low P & variable T) Movement of hot fluids (mostly water) >near magmas during crystallization Types of Metamorphism Metamorphism Hydrothermal (low P & variable T & fluids) >at hot springs and deep-sea black smokers Elevated P & T during mountain-building at convergent margins Types of Metamorphism Metamorphism Regional (variable P & T) Affects large areas (100's to 1000's km 2 ), typically in the lower crust Directed pressures may create foliated rock textures (slate, phyllite, schist, gneiss, etc.)slatephylliteschistgneiss Types of Metamorphism Metamorphism Regional (variable P & T) Crushing & shearing related to fault zones Creates foliated rocks (mylonites)mylonites Types of Metamorphism Metamorphism Cataclastic (dynamic) (localized high P & T) Meteorite impacts melt & shatter rocks (yielding breccia & glass) Types of Metamorphism Metamorphism Impact (ultra-high P & T) WWW Links in this Lecture > Metamorphism -> Metamorphic grade -> Index mineral -> Foliation -> Diagenesis -> Contact metamorphism - > Intrusion -> Quartzite -> Marble -> Hydrothermal metamorphism - > Regional metamorphism -> Slate -> Phyllite -> Schist -> Gneiss -> Cataclastic metamorphism - > Mylonite -