PowerPoint Presentationthe rock cycleSlide 3metamorphic rocks: controlling factorsSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12metamorphic rocks: basic classificationSlide 14Slide 15Slide 16Slide 17Slide 18Slide 19schist under microscopeSlide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32metamorphism and metamorphic rocksthe rock cyclemetamorphism• high enough temperature & pressure to “change” rocksbut not high enough to melt rocks…changes to rocks occur in the solid-state…• hot, reactive fluids also contribute• old minerals, unstable under new P, T conditions, re-crystallize into new minerals• metamorphism occurs at depth; cannotsee metamorphic rocks unlessthey are uplifted• new rocks are metamorphic rocksmetamorphic rocks: controlling factors• parent rock composition (also called protolith)• temperature and pressure during metamorphism• tectonic forces• fluidsno new material is added to rock during metamorphismif parent material contains only one minerallimestoneQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.marble (CaCO3)QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.limestone (CaCO3)parent rock compositionmetamorphic rock will have similar composition to parent rockresultant metamorphic rock will only have one mineral--mineral will be recrystallized (texture changes)--QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.limestone under microscope(stained)(note fragments of shells)marble under microscope(note interconnecting grains)texture changesif parent material contains many minerals…QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.garnet growing garnet schist (metamorphic rock)…old minerals will recombine to form new mineralsclay, quartz, mica, and volcanic fragments in a sandstonewill combine to form new metamorphic mineralsexample is garnet: which grows during metamorphismheat is essentialtemperature during metamorphism• heat from Earth’s deep interior• all minerals stable over finite temperature range• higher temperatures than range cause melting(and therefore generates igneous rocks)think about mixing flour, yeast, water, salt….….nothing happens until they have a heat source and then they make breadpressure in the Earth acts the same in all directionspressure is proportionalto depth in the Earthlook at example with deep waterpressure increaseswith depthvolume decreaseswith depthpressure during metamorphismincreases at ~1 kilobar per 3.3 kmhigh pressure minerals: more compact and dense--grains pack together--consequence on cube is squeezing into smaller cubetectonic forces - driven by plate motion!lead to forces that are not equal in all directions (differential stress)compressive stress (hands squeeze together)causes flattening at 90° to stressshearing (hands rubbing together) causes flattening parallel to stressflattened pebbles in metamorphic rockfluids• hot water (water vapor) most important• heat causes unstable minerals to release water• water reacts with surrounding rocks and transports dissolved material and ionstime• metamorphism may take millions of years• longer times allow new minerals to grow larger--coarser grained rocksmetamorphic rocks: basic classificationfoliated (layered)non-foliated (non-layered)type of foliation -- e.g. slatycomposition -- e.g. marblebased on rock texturefoliationfoliated (layered) metamorphic rocksresults from differential stress (not equal in all directions)non-foliated foliatedappearance under microscopefoliated metamorphic rock: slatefoliated metamorphic rock: slatefoliated metamorphic rock: phyllite (higher T, P than slate)garnetfoliated metamorphic rock: schist (higher T, P than phyllite)…new minerals grow -- garnet (large, roundish grains)schist under microscopeQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.garnetbanding of quartz/feldspar and ferromagnesian mineralsfoliated metamorphic rock: gneiss (higher T, P than schist)non-foliated (non-layered) metamorphic rocksresults from pressure: equal in all directionsnamed on the basis of their compositionQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.limestone (CaCO3)marble (CaCO3)Carrara Marble QuarryMichelangelo’s DavidQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.non-foliated metamorphic rocks: quartzitemetamorphosed quartz sandstonePhoto credit: R. WellerQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.non-foliated metamorphic rocks: hornfelsmetamorphosed basalttypes of metamorphismcontact metamorphism• occurs adjacent to magma bodies intrudingcooler country rock -- “contact”• produces non-foliated metamorphic rocks• happens in a narrow zone of contact(~1 to 100 m wide) known as aureole• forms fine-grained (e.g. hornfels) orcoarse-grained (e.g. marble) rockstypes of metamorphismregional metamorphism• occurs over wide region and mostly in deformedmountain ranges• produces foliated metamorphic rocks• happens at high pressures and over a range of temperature• increases in pressures and temperatures forms rocks ofhigher metamorphic gradeother types of metamorphism (less common)• produces migmatites, which have both intrusive andmetamorphic textures• occurs during impact eventspartial melting during metamorphismshock metamorphism• yields very high pressures• forms “shocked” rocks around impact cratersQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.migmatiteigneous and metamorphictextureshydrothermal alteration along mid-ocean ridgecold sea water encounters hot basalt, forms steam, alters mineralsQuickTime™ and aVideo decompressorare needed to see this picture.black smoker offshore Pacific Northwesthot steam/sea water cools as it emerges into ocean andprecipitates metalstemperatures cooler in down-going (subducting) plate(dashed purple line is isotherm -- line of equal T)plate tectonics and metamorphismregional metamorphism associated with convergent boundaries• pressure increases with depth• temperature varies laterally• different P, T conditions yield different