Laboratory Manual for Introductory Geology 4e

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InterpretingMetamorphicRocks7This banded quartzofeldspathic gneiss (pronounced nice) is an intensely metamorphosed rock.173
LEARNINGOBJECTIVES■■Understand the changes thatoccur during formation ofmetamorphic rocks■■Understand the agents thatbring about metamorphism■■Become familiar withmetamorphic textures andmineral assemblages■■Interpret the history ofmetamorphic rocks fromtheir textures and mineralassemblagesMATERIALSNEEDED■■A set of metamorphic rocks■■Magnifying glass or hand lensand, ideally, a microscope andthin sections of metamorphicrocks■ ■ Standard supplies foridentifying minerals (streakplate, glass plate, etc.)7.1 IntroductionBiologists use the term metamorphosis (from the Greek meta, meaning change, andmorph, meaning form) to describe what happens when a caterpillar turns into a butterfly.Geologists use the similar term metamorphism for the processes of changethat a rock undergoes when exposed to physical and chemical conditions significantlydifferent from those under which it first formed. The original rock, calledthe protolith, may be any kind of igneous, sedimentary, or older metamorphic rock.Logically, the end product of metamorphism is a metamorphic rock. Metamorphismdiffers from sedimentary and igneous rock-forming processes because it isentirely a solid-state phenomenon. This means that the original rock remains in a solidstate without breaking apart or melting. By definition, metamorphism occurs attemperatures higher than those involved in sedimentary rock diagenesis and lowerthan those at which melting takes place.Metamorphic rocks form at depths below those at which sedimentary rocksgenerally form and above those where melting generally occurs, so they may yieldimportant clues about parts of the Earth for which neither igneous nor sedimentaryrocks can provide information. For example, what happens to rocks as the oppositesides of the San Andreas fault grind past one another? Or to rocks along the westcoast of South America as the Nazca Plate is subducted beneath the continent? Orto rocks deep below Mt. Everest as India collides with Asia? How did rocks in Californiachange when they were intruded by the granitic magma that today forms theenormous Sierra Nevada batholith?This chapter shows how we can answer these questions and unravel the geologichistory of rocks that have been changed—sometimes dramatically—from their originalforms. We’ll begin by describing metamorphic changes and the agents thatcause them, and then examine metamorphic textures and minerals for clues to thetype of metamorphism that occurred and the temperature and pressure conditionsunder which it took place.7.2 What Changes during Metamorphism?Nearly all characteristics of the protolith may change during metamorphism,including its texture, its mineral composition, and even its chemical composition.In some cases, only one of these properties may change, but in others, two or allthree of them may change so much that the metamorphic rock looks nothing likeits protolith.7.2.1 Changes in TextureA rock’s texture includes the size, shape, and relationships of its grains. These propertiesmay change during metamorphism by any of three processes:1. Recrystallization (change in grain size and shape): Mineral grains may regrowto form new grains of the same mineral, changing in shape, size, or both2. Pressure solution (change in grain shape and relationships): If water is presentduring metamorphism, some minerals may partially dissolve and the ions mayre-precipitate, changing the shapes and relationships among grains.3. Alignment of grains (change in grain orientation): In most instances, mineralsin the protolith are oriented randomly, but during certain kinds of metamorphism,they become aligned parallel to one another. The resulting textures,called foliation and lineation, are described in section 7.3.3.174 CHAPTER 7 INTERPRETING METAMORPHIC ROCKS
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LABORATORY MANUALFOR INTRODUCTORY G
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CONTENTSPreface viiCHAPTER 1Setting
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CHAPTER 8Studying the Earth’s Lan
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PREFACEThis laboratory manual is ba
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exercises interspersed throughout t
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Supplements(available for download
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ABOUT THE AUTHORSAllan Ludman is Pr
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LEARNINGOBJECTIVES■ Understand ch
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One way to obtain more data would b
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TABLE 1.1 Basic definitions●●
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EXERCISE 1.2Reservoirs in the Earth
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EXERCISE 1.4Sources of Heat for Geo
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1.3 Units for Geologic MeasurementB
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FIGURE 1.5 Measuring the volume of
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FIGURE 1.6 The white cliffs of Dove
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MileFIGURE 1.7 Methods for dealing
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FIGURE 1.8 An example of the princi
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EXERCISE 1.9Name:Course:How Long Do
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APPENDIX 1.1Metric-U.S. Customary C
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LEARNINGOBJECTIVES■■Become fami
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plate between two continents, conti
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FIGURE 2.4 The Earth’s major clim
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More clues soon came from seismolog
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FIGURE 2.8 Magnetic reversals of th
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FIGURE 2.11 Rates of motion of the
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EXERCISE 2.7A Tale of Two RidgesNam
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EXERCISE 2.8Continental Rifting: Sp
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Even without any earthquake informa
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EXERCISE 2.10Estimating the Amount
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2.5.5 Hot Spots and Hot-Spot Tracks
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EXERCISE 2.11Name:Course:Determinin
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EXERCISE 2.12Name:Course:Long-Term
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GEOTOURS EXERCISE 2Analyzing Plate
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LEARNINGOBJECTIVES■ Understand wh
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When a mineral grows without interf
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FIGURE 3.1 Specimens of the mineral
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3.4.5 HardnessThe hardness of a min
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FIGURE 3.4 Crystals of some common
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FIGURE 3.6 Cleavage in common miner
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3.4.9 MagnetismA few minerals are a
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EXERCISE 3.7Identifying MineralsNam
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The minerals and elements we most r
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EXERCISE 3.9Mineral Resources in Yo
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GEOTOURS EXERCISE 3Extracting Miner
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APPENDIX 3.1Mineral Identification
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APPENDIX 3.2Determinative Tables fo
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APPENDIX 3.2Determinative Tables fo
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APPENDIX 3.3Common Minerals and The
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MINERAL PROFILE DATA SHEET NameSamp
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LEARNINGOBJECTIVES■■Understand
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FIGURE 4.1 The rock cycle.Heating a
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FIGURE 4.3 Typical grain shapes.(a)
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EXERCISE 4.2Describing a Rock’s T
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EXERCISE 4.3Understanding the Origi
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EXERCISE 4.4Interpreting the Textur
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■ Hardness: Use a steel safety pi
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FIGURE 4.6 Flowchart for determinin
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4.8 The Economic Value of RocksMost
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FIGURE 4.7 Examples of igneous, sed
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GEOTOURS EXERCISE 4Deciphering Land
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LEARNINGOBJECTIVES■■Become fami
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crystalline rocks. Those that are s
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EXERCISE 5.3Interpreting Igneous Co
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FIGURE 5.4 Volcanic glasscontains n
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EXERCISE 5.5Interpreting Fragmental
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Page 141 and 142: EXERCISE 5.8Insights from Melting a
Page 143 and 144: EXERCISE 5.9Explaining Features of
Page 145 and 146: extreme crustal stretching has expo
Page 147 and 148: EXERCISE 5.13Interpreting Plate-Tec
Page 149 and 150: FIGURE 5.12 Distribution of volcano
Page 151 and 152: FIGURE 5.14 Comparison of areas in
Page 153 and 154: EXERCISE 5.15Stratovolcano Disaster
Page 155 and 156: GEOTOURS EXERCISE 5Exploring the Na
Page 157 and 158: IGNEOUS ROCKS STUDY SHEET NameSampl
Page 159 and 160: LEARNINGOBJECTIVES■■Understand
Page 161 and 162: FIGURE 6.2 Chemical weathering of f
Page 163 and 164: FIGURE 6.3 The five steps in clasti
Page 165 and 166: 6.3.2 Chemical Sedimentary RocksChe
Page 167 and 168: 6.3.3 Biochemical and Organic Sedim
Page 169 and 170: TABLE 6.2 Classification of common
Page 171 and 172: FIGURE 6.5 Flow chart for identifyi
Page 173 and 174: FIGURE 6.6 Sediment sorting.(a) Poo
Page 175 and 176: EXERCISE 6.7Recognizing Sediment De
Page 177 and 178: FIGURE 6.9 Sedimentary rock beds.(a
Page 179 and 180: FIGURE 6.12 Cross bedding, a type o
Page 181 and 182: FIGURE 6.15 Fossils reveal remarkab
Page 183 and 184: FIGURE 6.16 Examples of depositiona
Page 185 and 186: EXERCISE 6.10Interpreting Sedimenta
Page 187: SampleTexture(grain size, shape,sor
Page 191 and 192: FIGURE 7.1 Examples of changes from
Page 193 and 194: FIGURE 7.2 Growth of metamorphic mi
Page 195 and 196: FIGURE 7.3 Types of stress.(a) Comp
Page 197 and 198: FIGURE 7.5 Photomicrographs of rock
Page 199 and 200: FIGURE 7.6 Varieties of gneiss form
Page 201 and 202: EXERCISE 7.2Identifying Metamorphic
Page 203 and 204: FIGURE 7.11 Settings of metamorphis
Page 205 and 206: EXERCISE 7.4Interpreting the Type o
Page 207 and 208: EXERCISE 7.5Name:Course:Index Miner
Page 209 and 210: Sample Minerals presentMETAMORPHIC
Page 211 and 212: Sample Minerals presentMETAMORPHIC
Page 213 and 214: LEARNINGOBJECTIVES■■Become fami
Page 215 and 216: EXERCISE 8.1Which Image Works Best?
Page 217 and 218: More sophisticated grid systems are
Page 219 and 220: EXERCISE 8.2The Latitude/Longitude
Page 221 and 222: EXERCISE 8.3Locating Points with th
Page 223 and 224: EXERCISE 8.4Locating Points with th
Page 225 and 226: But which north is north? No, this
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Page 229 and 230: 8.4 Vertical Exaggeration:A Matter
Page 231 and 232: GEOTOURS EXERCISE 8Locating Places
Page 233 and 234: LEARNINGOBJECTIVES■ Understand ho
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Page 237 and 238: FIGURE 9.5 Digital elevation model(
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250300300FIGURE 9.7 Hachured contou
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9.3.4 Rules and Applications of Con
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EXERCISE 9.6Name:Course:Survival of
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FIGURE 9.8 Map of the microwave tow
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FIGURE 9.11 The effect of vertical
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GEOTOURS EXERCISE 9Working with Top
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APPENDIX 9.1Topographic Map Symbols
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Interpreting GeologicStructures on
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of structures on the ground (the ma
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EXERCISE 10.2The Basic Types of Con
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EXERCISE 10.3Determining Strike and
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FIGURE 10.4 Block diagrams.Map view
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FIGURE 10.6 Block diagrams showing
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FIGURE 10.7 Hanging wall, footwall,
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is not the same as that of the beds
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EXERCISE 10.9Name:Course:Interpreti
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FIGURE 10.9 Geologic maps (continue
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EXERCISE 10.11Name:Course:Using Sym
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EXERCISE 10.12Name:Course:Construct
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EXERCISE 10.13Interpreting Simple G
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FIGURE 10.13 Structural control of
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10.6 Reading Real Geologic MapsYou
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FIGURE 10.14 (continued).Geologic M
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EXERCISE 10.18Making a Geologic Map
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GEOTOURS EXERCISE 10Name:Course:Und
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LEARNINGOBJECTIVES■■Understand
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S-waves (FIG. 11.2b) are seismic wa
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FIGURE 11.4 Worldwide distribution
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FIGURE 11.5 Travel-time curves show
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EXERCISE 11.4Name:Course:Locating a
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EXERCISE 11.4Locating an Earthquake
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EXERCISE 11.4Name:Course:Locating a
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EXERCISE 11.5Name:Course:Determinin
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11.5 Predicting EarthquakeHazards:
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EXERCISE 11.7Locating Liquefaction
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After watching dramatic images of t
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APPENDIX 11.1Seismic Analysis Works
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LEARNINGOBJECTIVES■■Determine t
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EXERCISE 12.2Relative Ages in Cross
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EXERCISE 12.3Applying the Principle
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EXERCISE 12.4Name:Course:Using Sedi
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FIGURE 12.6 How the three kinds of
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EXERCISE 12.5Name:Course:Decipherin
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becoming extinct. When we find an i
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EXERCISE 12.6Name:Course:Dating Roc
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FIGURE 12.9 Changing parent:daughte
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EXERCISE 12.7Putting It All Togethe
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EXERCISE 12.8What Numerical Ages Ca
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EXERCISE 12.9Correlation (continued
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EXERCISE 12.10Cretaceous Paleogeogr
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Landscapes Formed13by StreamsStream
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EXERCISE 13.1Differences between St
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EXERCISE 13.2Why Some Streams Meand
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RFIGURE 13.5 The Genesee River sout
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EXERCISE 13.2Why Some Streams Meand
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FIGURE 13.8 A floodplain and its as
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ST. FRANCIS CO4070797064UNION PACIF
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1000Big900900B I G H I L LARKANSAS9
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FIGURE 13.13 Major drainage basins
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anchWTJ54MurphyNew BloomfieldTown65
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EXERCISE 13.6Recognizing Stages of
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MT T L E62446267DogRock757266170634
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13.7 When Streams Don’t Seemto Fo
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EXERCISE 13.7Deducing the History o
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13.8 When There’s Too Much Water:
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EXERCISE 13.9Estimating Potential F
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13.9 Streams, Society, and the Envi
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Groundwater as aLandscape Formerand
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EXERCISE 14.1Factors Affecting Infi
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EXERCISE 14.1Name:Course:Factors Af
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FIGURE 14.2 Groundwater landscape e
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60075000750600FIGURE 14.4 Karst top
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FIGURE 14.5 The water table separat
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EXERCISE 14.4Effects of a Changing
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100100100FIGURE 14.9 Karst topograp
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4400B a l d r i d g e C a n y o n42
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EXERCISE 14.7Name:Course:Environmen
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EXERCISE 14.8Name:Course:Environmen
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Glacial Landscapes15These jagged mo
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FIGURE 15.2 Mountain and continenta
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EXERCISE 15.1Comparison of Glaciers
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EXERCISE 15.3Erosional Features of
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15.3.2 Depositional LandscapesLands
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EXERCISE 15.4Landforms at the Termi
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900900800BOWEN1000700C R E E K900RO
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450400LEMON400ROADSLAYTON4504503Spo
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15.4 Landscapes Producedby Mountain
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The base level for a tributary stre
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3700380036003900Northwest BasinLake
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FIGURE 15.17 Atmospheric temperatur
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GEOTOURS EXERCISE 15Flowing Ice as
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GRID: 10/inch = 39,4/10cm
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Processes and Landforms16in Arid En
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FIGURE 16.2 Types of arid regions.(
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16.2 Processes in Arid RegionsNow l
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16.3 Progressive Evolution of Arid
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EXERCISE 16.3Interpreting Arid Land
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EXERCISE 16.3Interpreting Arid Land
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RiverGila85WatermanWashR A I N B O
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85130011001000FIGURE 16.8 Topograph
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FIGURE 16.10 Characteristics and ev
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400040004000L o w e V a l l e y4100
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FIGURE 16.13 Vulnerability to deser
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Shoreline Landscapes17Coastlines co
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FIGURE 17.1 Types of shorelines.(a)
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EXERCISE 17.1Erodibility and Stabil
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17.2.5 Emergent and Submergent Shor
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1382427FIGURE 17.5 Maine coastline
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EXERCISE 17.5Measuring Sea-Level (a
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FIGURE 17.7 Area just south of Lake
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17.3.2 Coastal Erosion and Depositi
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FIGURE 17.11 Erosional features of
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EXERCISE 17.7Erosional Processes an
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17.3.5 Depositional FeaturesPromine
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EXERCISE 17.9Depositional Processes
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FIGURE 17.18 The shoreline of theno
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FIGURE 17.21 Aerial view showing ho
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EXERCISE 17.10Name:Course:Unintende
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FIGURE 17.24 Counterclockwise wind
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EXERCISE 17.11Name:Course:Effects o
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FIGURE 17.27 Flooding caused by hur
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EXERCISE 17.12Effects of Storm Path
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GEOTOURS EXERCISE 17Understanding T
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LEARNINGOBJECTIVES■ Explain why p
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EXERCISE 18.1Humans and Earth Syste
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EXERCISE 18.2Short-Term Changes in
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Weather describes atmospheric condi
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FIGURE 18.5 The greenhouse effect.G
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EXERCISE 18.3Name:Course:Assessing
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FIGURE 18.8 Movement of water from
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FIGURE 18.10 Projected sea-level sc
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EXERCISE 18.4Effects of Sea-Level R
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FIGURE 18.13 Estimated human popula
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FIGURE 18.14 Two bird species hunte
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EXERCISE 18.6Name:Course:How Quickl
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GEOTOURS EXERCISE 18Inducing Change
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Courtesy of Allan Ludman; p. 162 (t
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270 280260240 250290 300Clay310 320
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Align with northern latitude tick m
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Laboratory Manual for Introductory Geology 4e

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