Chapter 7 Lecture Notes
Chapter 7 Lecture Notes GEO 101-007
Popular in The Dynamic Earth
verified elite notetaker
Popular in Geology
This 7 page Class Notes was uploaded by Jennifer Gintovt on Monday September 28, 2015. The Class Notes belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 40 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
Reviews for Chapter 7 Lecture Notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 09/28/15
GEO 101007 92315 Chapter 7 Metamorphism A Process of Change Smith Hall Constructed 1910 Named after Eugene Allen Smith 1841192 7 0 Alabama native Fought in Civil War Witness campus burning Became state geologist Believed Alabama s natural resources coal etc could help struggling Alabama economy following the war 0 O O 0 Eugene Allen Smith Geologist Professor Naturalist Violinist Sports enthusiast o 1917 UA Football Team What type volcano is Olympus Mons Shield Largest known volcano in solar system Mars Rock Cycle Illustrates the different processes and paths as Earth materials change both on the surface and inside the earth What is a Metamorphic Rock Rocks that form when preexisting rock changes into new rock as the result of an increase in pressure and temperature and or shearing under elevated temperatures Metamorphism occurs without the rock first becoming a melt or sediment Hot water can also play a role NOT MELTING THE ROCK Metamorphism Example Igneous Metamorphic Rock Rock pressure Granite Gneiss GEO 101007 92315 Key Term the original rock from which a metamorphic rock formed In the example above granite is the protolith ames Hutton Father of Modern Geologyquot Lived in Scotland Developed the principle of uniformitarianism Was puzzled by certain rocks that seemed to have been formed as other rocks do but had been distorted in structure Rock Metamorphism Basics Solid state change due to change in preexisting rock s environment 1 Temperature change 2 Pressure change 3 Compression and shear become relevant 4 Hot water hydrothermal uid added to the system 5 Or a combination of one or more Environmental change produces new minerals that did not occur in protolith andZor produces a new texture Changes to Protolith Environment Increase temperature addition of heat helps to break chemical bonds allowing atoms to move and form new bonds which means new minerals Increase pressure tremendous pressures can cause atoms to pack more closely together sometimes forming new minerals Increase pressure and temperature certain minerals are stable at specific temperatures and pressures 0 Changing these variables promotes new mineral formation Exposure to very hot water hydrothermal uid from slide 16 metasomatism the process of changing a rock s chemical composition by reactions with hydrothermal uids Compression and Shear Vertical compression force is applied down on an object example gravity Horizontal compression force is applied to the sides of an object example convergent plate boundary GEO 101007 92315 Shear force is applied in opposite directions on an object example pushing a deck of cards to one side or the other Results of Compression and Shear Equant Grains roughly same dimensions in all directions Inequant Grains dimensions are not the same in all directions Preferred Orientation alignment of inequant grains Distinguishing Features of Metamorphic Rocks Helps us to classify them Metamorphic texture The arrangement of grains formed as result of metamorphism Metamorphic minerals specific new minerals grow only under metamorphic temperatures and pressures Metamorphic foliation parallel alignment of platy minerals such as mica and or the presence of alternating lightcolored and darkcolored bands Metamorphic Processes 1 Recrystallization 339 Changes the shape and size of grains without changing the mineral chemistry grains ten to get bigger but not always 2 Phase change 339 Changes one mineral to another mineral of the same composition but different crystalline structure atoms rearrange 3 Metamorphic reaction neocrystallization 339 Results in new minerals that differ different chemical composition from those of the protolith 4 Pressure solution 339 In the presence of water grains are dissolved on the sides undergoing more pressure and precipitate new mineral where the pressure is lower water helps atoms move easierquicker 5 Plastic Deformation 339 Grains change shape texture without breaking due to compression at high heat and soft plasticlike nature of rock Two Fundamental Classes of Metamorphic Rocks 1 Foliated metamorphic rocks distinguished by their component minerals grain size and by the nature of their foliation 339 Ex Gneiss 2 Nonfoliated metamorphic rocks primarily divided up by their component minerals what it is made of 339 Ex Quartzite GEO 101007 92315 Common Examples of Foliated Rocks 1 Slate I Finegrained foliated metamorphic rock I Protolith shale or mudstone high clay content I Relatively low pressures and temperatures I Strong foliation slaty cleavage breaks easily into sheets 2 Phyllite I Finegrained with foliation caused by the preferred orientation of very fine grained white mica I Protolith slate neocrystallization of clay to produce white mica I Relatively low pressures but higher temperatures I Silky sheen called phyllitic luster 3 Metaconglomerate I Same metamorphic conditions as slate and phyllite pressure solution and plastic deformation atten pebbles and cobbles into pancakelike shapes I Alignment of clasts pebblescobbles defines foliation I Protolith conglomerate 4 Schist I Mediumtocoarsegrained I Foliation schistosity which is defined by the preferred orientation of large mica akes I Forms at higher temperatures than phyllite I Various protoliths 5 Gneiss I Typically composed of alternating light and dark bands with each band having a specific composition mafic vs felsic minerals I Foliation is gneissic banding which gives it a stripped appearance I Protolith had alternating beds of sandstone and shale or caused by extreme amounts of shearing rock ows like plastic I Various protoliths 6 Migmatite I Extreme conditions where gneiss may begin to melt but the partial melt quickly freezes resulting in part igneous part metamorphic rock Examples of Mica I Range of colors but has perfect cleavage in one direction sheetlike I Can be associated with metamorphic rocks Nonfoliated Metamorphic Rocks Common Examples 1 Hornfels I Contain a variety of metamorphic minerals which is based on minerals found in protolith and the temperature pressure of metamorphism 2 Quartzine I Protolith is pure quartz sandstone quartz grains recrystallize creating new grains sugary texture GEO 101007 92315 3 Marble fossiliferous limestone marble 7 vquot V quot f 0 a f 39s3939 A n I Protolith is limestone which recrystallizes so that fossil shells pore spaces grains and cement become a solid mass of calcite Degree of Metamorphism I Metamorphic grade indicated the intensity of metamorphism or the degree of metamorphic change 0 Low or high grade ing pressure GEO 101007 92315 Geologic Setting of Metamorphism 1 Contact thermal gt Temp of the protolith rises due to heat transfer from nearby magma gt Hydrothermal uids also play a role in metamorphosis gt The zone of alteration that is in contact with the magma is called metamorphiccon tact aureole Contact Metamorphism Aureole W quot 1 I r gt Does not involve increase in pressure and differential stress 0 Would you expect to find foliated metamorphic rocks in association with contactthermal metamorphism I No because differential pressure is not present Nonfoliated hornfels would be common gt Metamorphic Contact Aureole zone of alteration that varies in width depending on the size and shape of the magmatic intrusion as well as the amount of hydrothermal circulation present 2 Burial gt Metamorphism due only to the consequences of very deep burial 8 15km gt Temperature and pressure increase with depth gt Lowgrade metamorphism 3 Dynamic gt Occurs at faults surface on which one piece of crusts slides at great depth gt10 Km gt Minerals in warm rock recrystallize get smaller and form the highly foliated metamorphic mylonite gt Form due to shearing alone Mylomte very tiny grains O Igmal rock GEO 101007 92315 4 Dynamothermal regional gt Occurs during mountain building convergent plate boundary gt Some rock is pushed up mountains while some rock is pushed down Increased temp with depth Increased pressure with depth Increased compression and shear due to convergence gt Grade of metamorphism increases with depth gt Eventually mountains are eroded away and metamorphic rocks formed at depth rise and are visible at the Earth s Surface gt LARGE SCALE 5 Hydrothermal gt Chemical alteration caused when hot ionrich uids circulate through cracks gt Common at midocean ridges 6 Subduction Zones gt Produces metamorphic rock called blueschist gt Rare combination of high pressure but low temperature 7 Shock gt Shock waves caused by highenergy events such as a meteorite impacts can change minerals quartz changes to coesite 39
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'