薄片岩石学1

薄片岩石学课程编号：01211110开课学期：1周学时/总学时：2/36学分：2英文名称：PetrographyRock=mineralassemblage+fabricChemicalcomposition+PTPT+deformationThermodynamicsTexture&structureQuartz+plagioclase+biotite+K-feldspar?Howtodistinguishigneous,sedimentaryandmetamorphicrocks?Quartz+plagioclase+biotite+K-feldspar?Biotitegranite;Biotitetwo-feldspargneissBiotiteschistGreywackePhaneriticrockwith10%felsicminerals.Quartz-richGranitoid909060602020AlkaliFs.QuartzSyeniteQuartzSyeniteQuartzMonzoniteQuartzMonzodioriteSyeniteMonzoniteMonzodiorite(Foid)-bearingSyenite5103565(Foid)-bearingMonzonite(Foid)-bearingMonzodiorite90AlkaliFs.Syenite(Foid)-bearingAlkaliFs.Syenite10(Foid)Monzosyenite(Foid)MonzodioriteQtz.Diorite/Qtz.Gabbro510Diorite/Gabbro/Anorthosite(Foid)-bearingDiorite/Gabbro60(Foid)olitesQuartzoliteGraniteGrano-dioriteQAPF60•QAPFdiagram•Anorthosite:90%plag•Gabbro35%maficmineras•Diorite35%maficminerals•Granite25%maficminerals•15%quartz,15%k-spar,70%plag•Rockname?Rockclassificationbasedonchemistry•Silicaconcentrationprincipaloxide•SilicicrockswithSiO2•66wt%silicaisfelsic•52-66wt%silicaintermediate•45-52wt%silicaismafic•45wt%silicaisultramafic•Also:–Magnesian,aluminous,alkaline(Na2OandK2O)ClassificationofIgneousRocksFigure2-4.Achemicalclassificationofvolcanicsbasedontotalalkalisvs.silica(TAS).AfterLeBasetal.(1986)J.Petrol.,27,745-750.OxfordUniversityPress.MineralsBowenreactionseriesTexturesandstructuresInarockwithaphaneritictexture,whereallgrainsareaboutthesamesize,weusethegrainsizerangesshowntotherighttodescribethetexture:2mmfinegrained2-5mmmediumgrained5-3cmcoarsegrained3cmverycoarsegrainedporphyritictextureIgneousTexturesFigure3-5.a.Compositionallyzonedhornblendephenocrystwithpronouncedcolorvariationvisibleinplane-polarizedlight.Fieldwidth1mm.b.Zonedplagioclasetwinnedonthecarlsbadlaw.Andesite,CraterLake,OR.Fieldwidth0.3mm.©JohnWinterandPrenticeHall.Figure3-8.Ophitictexture.Asinglepyroxeneenvelopsseveralwell-developedplagioclaselaths.Width1mm.Skaergårdintrusion,E.Greenland.©JohnWinterandPrenticeHall.Figure3-11.b.Resorbedandembayedolivinephenocryst.Width0.3mm.©JohnWinterandPrenticeHall.Figure3-11.c.HornblendephenocrystdehydratingtoFe-oxidespluspyroxeneduetopressurereleaseuponeruption,andesite.CraterLake,OR.Width1mm.©JohnWinterandPrenticeHall.Figure3-13.Flowbandinginandesite.Mt.Rainier,WA.©JohnWinterandPrenticeHall.Figure3-15.Intergranulartextureinbasalt.ColumbiaRiverBasaltGroup,Washington.Width1mm.©JohnWinterandPrenticeHall.DuniteAlmostallofthegrainsinthisrockareolivine.Notethehighorderinterferencecolorsofolivineandtheminorsecondarycalcitewhichoccursasveinletsthroughthesample.HypersthenegabbroPlagioclaseandhypersthene(orthopyroxene)dominatethisrock.Thisslidemayhavebeencutalittletoothick,accountingforthehigher-than-expectedinterferencecolorsofthehypersthene.BiotiteGraniteMineralsinthisrockincludequartz,plagioclase,biotite,andK-feldspar.Notetheminormyrmekiteinthissample.MyrmekiteMyrmekitictexturedefinedbywormy(rounded)intergrowthsofquartzandK-feldsparinplagioclasewhichisadjacenttoK-feldspar.Probablyformsasaresultofsubsolidusexchange.Comparethistexturetomicrographictexture.Sub-grainsinquartzThecrystalstructureofthisquartzgrainhasbeendeformed(probablybylow-grademetamorphism)toproducesub-grains.TonaliteThisrockcontainshornblende,plagioclase,clinopyroxene,biotite,andquartz.Noticehowthehornblenderimsthesmallcoreofrelictclinopyroxeneinthecenterofthisphoto,indicatingareactionrelationship.AmygdaloidaltextureTheovalfeatureinthisphotomicrographisanamygdule:aformerlyopenvesiclewhichhasbeenfilledwithasecondarymineral(s)precipitatedfromlow-Tgroundwaterswhichhavepenetratedintotherock.Inthiscase,theamygduleisprobablyfilledwithazeolitemineral.KomatiiteKomatiitesarerareultramaficvolcanicrocks.Thissampledisplaysthecharacteristicspinifextexturedefinedbyextremelyacicularolivinephenocrysts--probablyasignofrapidcrystallizationfromasignificantly-undercooledmagma.SedimentaryRocksSedimentaryrockscanbedividedintothreefundamentaltypesbasedupontheoriginoftherock.Clasticsedimentaryrocksareformedfromthefragmentsofotherrocksorminerals.Chemicalsedimentaryrocksareformedwhendissolvedionscarriedinsolution(usuallyseawater)areprecipitated.Organicsedimentaryrocksformfromthedeadremainsofplantoranimals.Clasticsedimentaryrocks:Clasticsedimentaryrocksareformedinthreestepsthatrequire:generationofsediments;transportationofsediments;depositionofsediments.ArkoseSandstoneArkosesarefeldspar-richsandstones(75%quartz,ratiooffeldspartorockfragmentsgreaterthan3:1).Thephotoaboveisundercrossedpolarizers.Abundantsodicplagioclase(multipletwins,partiallyalteredtoclays)andmicrocline(basketweavetwins)areinagrain-supportedmatrix.ShaleShalesandmudstonesarethemostabundantsedimentaryrocktypes.Theyconsistprincipallyofveryfine-grainedclaysandotherminerals.Thephoto,undercrossedpolarizers,hasafieldofviewof0.3mm.Thewhitegrainsarequartz,andthedarkmatrixisamixtureofvariousclayminerals.QuartareniteQuartzarenitesarepurequartzsandstones(95%quartz),oftenrepresentingreworkedsedimentarydeposits.Thephoto,unde