Presentation on theme: "Rocks: Sedimentary Igneous Metamorphic Keepers of Earth’s History 1."— Presentation transcript:
1 Rocks:SedimentaryIgneousMetamorphicKeepers of Earth’s History1
2 Granite What’s in your rock?: Hornblende Orthoclase Quartz aggregates of mineralsBiological materialFossil fragmentsPlant material3
3 Understanding rocks is the basic foundation of knowledge for earth scientists and materials thatmake up the earth.Every rock “speaks” to the observer and givesclues about where and how it was formed.Rocks are divided into 3 major groups:Igneousformed from solidifying hot moltenrock (magma)Sedimentaryformed on the surface of the earth fromweathering processesMetamorphicpre-existing rocks are subjected tovarious pressure and temperaturerelationships4
4 All rocks are identified based on their texture and composition. How does an earth scientist distinguish betweenthe three rock types (Ig, Seed, and Met)?Texture:the appearance of the rocksize, shape, and arrangement of mineral grains.Composition (mineral assemblages)types and relative proportions of mineralsmaking up a rockcomposition, mineral make-up, chemistry--allindicators of a rock’s compositionAll rocks are identified based on theirtexture and composition.5
6 where the earth’s internal forces meet The Rock Cycle:where the earth’s internal forces meetthe earth’s external forces (at the earth’ssurface)7Earth’s internal forcesEarth’s external forcesthe hydrosphere (HC)atmosphereerosion (wind, water, ice)biosphere activitiesmoving continents (PT)earthquakeselevation of mountainsvolcanic eruptionsProduce a continuous cycle of rising mountains only to beweathered down and uplifted repeatedly. As a result, igneoussedimentary, and metamorphic rocks are created.
7 I Earth Science, especially the rock cycle !!!!!!!!!!!!! 8 Discuss with a friend:Briefly identify each rock group andits geologic environment.2. Draw the rock cycle, and explain how therock cycle works to your neighbor.3. Why is the rock cycle a “cycle”???I will get an A on my exams and quizzes.
9 Magma Extrusive - igneous rocks – above the earth’s surface the parent material for igneous rocks (if not all rock groups)typical temperature 1,200oC (2,200oF)forms about 250 km or 150 miles below the earth’s surfaceExtrusive - igneous rocks – above the earth’s surfacevolcanic rockslava flowsExample – Hawaiian VolcanoesIntrusive - igneous rocks – below the earth’s surfaceplutonic rockslarge granite mountainsExample – Sierra Nevada Mountain Range10Grain size determines if the ig rock is extrusive orintrusive. Magma determines the rock’s composition.
10 surface (fine-grained) surface (coarse-grained) When observing “frozen magma” (an igneous rock), howdoes a geologist know if the rock is an Extrusive orIntrusive igneous rock?checking the crystal size - Does the rock contain visiblecrystals, or are crystals non-existent?Igneous Rock TexturesFactors that affect crystal size in an igneous rock:The rate at which magma coolsslow cooling – visible mineralsrapid cooling – non-visible mineralsvisible mineralsslow cooling magmaintrusive ig rocknon-visible mineralsrapid cooling magmaextrusive ig rockCooled above thesurface (fine-grained)Cooled below thesurface (coarse-grained)11
11 Composition of Igneous Rocks 14 How much silica (SiO2) is in your igneous rock?Felsic compositions (feldspar + silica)light-colored igneous rockscommon minerals: feldspar and quartz70% SiO2Intermediate compositions:mixture of felsic and mafic mineralsabout 60% silica (SiO2)Mafic compositions (magnesium + iron)dark-colored igneous rockscommon minerals: olivine and pyroxene50% SiO2ultramafic: composed entirely of olivine and pyroxeneand less than 50% silica (SiO2)
12 How are igneous rocks classified? Using their TEXTURE and COMPOSITION Igneous rocks are classified based on TEXTURE andCOMPOSITION.COMPOSITIONFelsic (light color)70% silicaIntermediate color60% silicaMafic (dark color)50% silicaphaneriticCOARSEGraniteDioriteGabbroTEXTUREaphaniticFINERhyoliteAndesiteBasaltIgneous rocks have the same chemistry butdifferent textural characteristics due to the typeof geologic environment (cools quickly or slowly).
13 I Earth Science, especially igneous rocks. What is the difference between extrusiveand intrusive igneous rocks?2. How can one tell the difference betweenan extrusive and intrusive rock texture?3. The composition of a mafic ig rock is….The composition of a felsic ig rock is ….4. A fine-grained, light-colored ig rock iscalled a ………………….I will get an A on my exams and quizzes.17
15 How is a sedimentary rock formed??? 19 Why is the earth’s surface 75% sedimentary rocks?erosionPre-existingRocksedimentwater, wind,icebreaks downpre-existing rockRiversDepositedtransportedLakeslithifiedcompactedcementedSedimentaryRock
16 Erosional processes – later (Chapter 4) 21Erosional processes – later (Chapter 4)Sediments are separated into 3 broad categories:Clastic sediments:inorganic grains or mineral fragments ranging insize from boulders to clay particles (flour size)Chemical sediment:formed by the precipitation of minerals dissolvedin lakes, rivers, or seawater environmentsBiogenic (bioclastic) sediment:sediment composed of animal and plant remains ormaterial precipitated by biological processesTo be a sedimentary rock, it must be lithified.
17 Lithification: processes by which sediment is transformed into sedimentary rockSediment can be lithified in three common processes:Compaction: Overlying weight of the sediment “squeezes”and compresses pore spaces, which pushes particles together.A. loose, unconsolidated sediment withabundant pore spaceB. compacted, compressed sediment withreduced pore spaceABCementation: Pore water is expelled from voids, and risingwater carries iron, calcium carbonate, and silica which precipitatesas geological glue (cement) holding the grains together.Grains are cemented together by threetypes of cements:iron cementcalcium carbonate cementsilica cement22
18 Grain boundaries convert compositions, “cementing” Lithification processesRecrystallization: Overlying pressure causes less stableminerals to convert to more stable minerals, producing newsubstances that cement pre-existing grains.Grain boundaries convertto more stable mineralcompositions, “cementing”grains together.Overlying pressure23
19 Clastic Sediment: conglomerate sandstone siltstone shale 24 lithified gravel sediment rangingfrom pea-sized to largerconglomeratelithifiedsand-sized particles (fine to coarsesandpaper)sandstonelithifiedfiner particles – size of table saltsiltstonefinest sedimentaryparticles (flour-size)lithifiedshale24
20 Chemical Sediments and Sedimentary Rocks Chemical Sediment: sediment formed by the precipitationof minerals dissolved in a lake, river, or seawaterAll surface water and groundwater containdissolved ions (chemicals), creating a venue forprecipitation of chemical sediment.Precipitation of chemical rocks takes place in two ways:Plants and animals alter the chemical balanceof the water body (lake, ocean).Increasing amounts of calcium carbonatecause precipitation of limestone.evaporation of chemically saturated waterbodies26
21 Evaporation of chemically saturated water creates a chemical sedimentary rock (evaporite).Na+Na+Cl-a lake containing sodium (Na+)and chlorine (Cl-)--free ionsCl-Cl-Na+Na+Cl-EvaporationLake water is evaporated,concentrating sodium andchloride ions (saturation).Sodium and chlorine combineto form halite (table salt).NaCl27
22 The Great Salt Lake, Utah (evaporite halite)28As lake becomes saturated,density of water increases.Utah
23 Chemical – sedimentary rocks that have been precipitated or are the result of evaporationGypsum – evaporite CaSO4Halite – evaporiteNaClLimestone--precipitatedcalcium carbonate29
24 Biogenic Sediments and Biogenic Rocks: Biogenic sediment is composed of organic remains of plants andanimals (bioclastic rocks).shell, bones, teeth, plant fragments, wood, roots30Common Biogenic Rocks:Limestonemost abundant biogenic sedimentary rockcomposed of calcium carbonate CaCO3(calcite, dolostone,aragonite)lithified shells, skeletal materialChertcomposed of silica SiO2precipitated silica shells (made by sea animals) that protectmicroscopic sea animals – Animals die, and silica shellssink, creating layers of chert beds on the ocean floor.“When the animal dies, it loses the chert off its back.”
25 Common Biogenic Rocks 31 Peat to Coal Peat Anthracite coal accumulated remains of terrestrial plantswith time and pressure ---- peatcontinued pressure and lithification coallithificationPeatIncreasing pressuremetamorphismAnthracite coalBituminous coal
26 Biogenic (bio-clastic) rocks – result from animal and plant secretions -- The term“clastic” indicates that these rocks contain fossils orparts of plants, shells, compacted plant materialAnimal partsCemented shell fragmentsFossil LimestoneMicroscopic fossilsCoquina32Chalk
27 What do sedimentary rocks tell the earth scientist? These rock “layers” weredeposited one layer at atime and lithified.The banded appearanceis known as bedding orgroups of layers called strata.The boundary betweeneach stratum is called abedding surface.Bedding surfacebeddingstrataBy observing the sedimentary rock type (clastic, chemical,biogenic) and depositional patterns, an earth scientist candecipher the geologic history – like reading pages in a book.33
28 Sedimentary Rock Classification Summary Tree Sedimentary Rocks are divided into 3-classification categories:Clastic sedimentsChemical sedimentsBio-clastic (chemical)sedimentsformed by precipitationcomposed of“animal parts”composed of inorganicgrainsfromplants andanimalsevaporationprocessesClassification based onObserved fossils, animal parts,Plant/animal secretionsclassification based ondistribution of grain sizesClassification based onlack of grains and chemicalcompositionFossil-limestoneConglomerateGypsum (CaSO4)SandstoneCoquinaDecreasing grain sizeSiltstoneHalite (NaCl)ChalkShaleLimestone (CaCO3)
29 I sedimentary rock classification. 36 Discuss with a friend: Describe at least 2 characteristics ofeach sedimentary rock classification(clastic, biogenic, chemical).Give a rock example for each classification.I will get an A on my exams and quizzes.
31 What is “metamorphism?” meta (change) morphism (form)transformation of pre-existingrock to a metamorphic rockthrough pressure andtemperature relationshipsAll changes take place throughsolid state transformation.38
32 takes place around 150oC (Temperature) Types of Metamorphismtakes place around 150oC (Temperature)typically at depths of 5 km below theearth’s surface (Pressure)At this temperature and pressure, new mineralsare formed – changed from one mineral toanother.39
33 I metamorphic rocks. Discuss with a friend: How do you define metamorphism? – Bespecific.What two major factors are necessaryfor pre-existing rocks to becomemetamorphosed?3. Where does metamorphism typicallytake place within the earth?I will get an A on my exams and quizzes.40
34 2 Common types of metamorphism contact metamorphismregional metamorphism44
35 What is contact metamorphism? magma “contacts” solid rock –heat is transferred into overlyingrocks through conduction – changingthe pre-existing rock it intrudedhigh heat/low pressurelocalized metamorphism“fast-acting,” like touching ahot frying pan45
36 Country rock (surrounding) is baked from conduction. 46
37 What is regional metamorphism? Pre-existing rock is subjected to intensestresses and strains (deformation) usuallyfrom the forces of mountain building.high heat/high pressurevery widespread geographicallylike experiencing a slow sunburn47
39 I the different ways to create Metamorphism. Discuss with a friend: Describe the conditions necessary for eachtype of metamorphism:contact metamorphismregional metamorphismI will get an A on my exams and quizzes.49
40 Metamorphic heat sources: contact with hot magma – heat penetratesoverlying rocks (conduction)geothermal gradient – heat increases withdepth – rocks are hotter when buried50
41 51 Geothermal Gradient Steep gradient Temperature increases as depth increases.Large thermal gradientis at the surface.Gradient decreasesafter 1000 km depth.Steep gradient100020003000400051
42 Pressure – increases with depth, Pressure associated with metamorphism52Pressure – increases with depth,various types of pressure rearrangeminerals – minerals compact or elongateConfining pressureDifferential pressure
43 How does one know how much metamorphism has taken place in a rock? 53How does one know how much metamorphismhas taken place in a rock?reflected in the rock’s textureMetamorphosed – mineralgrains are in a preferreddirection -- FOLIATIONNot Metamorphosed
44 I to metamorphose. 54 Discuss with a friend: Describe two heat sources associated withmetamorphism.Define the differences between confiningand differential pressures.3. Draw a diagram that shows mineralorientation due to confining anddifferential type pressures.I will get an A on my exams and quizzes.