显微构造地质学 microstructure 中英双语复习资料文档格式.docx
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isthepervasivebrittlefracturingandgranulationofrocks,generallyalongfaultsandfaultzones.Itproducesanaggregateofhighlyfracturedgrainsandrockfragmentsinamatrixofevensmaller,crushedgrains.Onceformed,suchcrushedaggregatesareabletoflowbyrepeatedfracturing,frictionalsliding,andrigid-bodyrotationofgrainsandfragments,aprocesstermedcataclasticflow.Cataclasticrocksarecharacterizedbypervasivecracksandgenerallysharp,angulargrainsandfragments.Oftensimilaratallscaleofobservation.Cataclasitefabric:
angularfragmentsofallsizes,sometransectinggrainboundaries,areembeddedinafine-grainedmatrix.Manylargerfragmentsarecrossedbyhealedfractures,alignedwithfluid-andsolidinclusions.Recrystallisedfabricofsmallnewgrainsthatgrewattheexpenseofoldgrains.Thenewgrainsshowlittlevarietyingrainsize.4.Dissolution-Precipitation溶解-沉淀Inrocksthatcontainanintegranularfluid晶间液体pressure-solutioncanoccurasdeformationmechanism.Pressure-solution:
dissolutionatgrainboundariesinagrainboundaryfluidphaseathighdifferentialstress.Pressuresolutionislocalisedwherestressinthegrainishigh,mostlywheregrainsareincontactalongsurfacesatahighangletotheinstantaneousshorteningdirectionthegrainlatticenearcontactpointsismorestronglycompressedthanelsewhere;
asaresult,materialwilldissolvenearthesecontactpointsandberedepositedatsitesoflowdifferentialstress.Alocallyhigherdensityofcrystaldefectsnearcontactpointsmayalsoenhancesolubility5.Processesofdissolutioncreep溶解蠕变(压溶作用)低温低应力低应变速率实质是coble蠕变3processes:
dissolutionatthesource,diffusionormigrationofthedissolvedmaterialalongsomepathwayreprecipitationDissolution:
Inresponsetoanapplieddifferentialstress,grainsbecomepreferentiallycorrodedalongsegmentsofgrainboundariesthatarebeingsubjectedtohighcompressivestress.Suchsegmentsincludethoseorientedathighanglestothegreatestprincipalcompressivestress
(1)andthoseinwhichrigidgrainsorobjectsimpingeononeanothertoconcentratestress.highlysolublemineralswilldissolvepreferentiallytothosewithlowersolubilities.Inimpurecarbonaterocks,forexample,calcitetypicallydissolvesmorereadilythanquartz,clays,andiron-manganeseoxides.Grainswithimpuritiesandthosewithcrystallinelatticesthathavebeensomehowdamaged,perhapsbytheworkofotherdeformationmechanisms,arelikewisemoresusceptibletodissolutionthanpristine原始的grains.溶解:
响应于施加的差异应力,晶粒优先被沿着受高压应力的晶界区段腐蚀。
这些部分包括与最大主压应力
(1)成高角度取向的部分,以及刚性颗粒或物体相互碰撞以集中应力的部分。
高度可溶的矿物质将优先溶解于溶解度较低的矿物质。
例如在不纯的碳酸盐岩中,方解石一般比石英,粘土和铁锰氧化物更容易溶解。
含有杂质的晶粒和晶格已经受到某种程度损坏的晶粒,也许是由于其他变形机制的作用,同样比原始晶粒更容易溶解。
Migrationandreprecipitation:
Assolidgrainsdissolve,theyenrichthefluidintheirconstituents,especiallynearsitesofmorerapiddissolution.Incontrast,littleornodissolutionmayoccurneargrainboundariesnormaltotheleastprincipalcompressivestress(3).Thedifferencesindissolutionratesresultinchemicalconcentrationgradientswithinthefluid,causingdissolvedconstituentstodiffuseawayfromthedissolutionsitesandtowardsitesoflowercompressivestress.迁移和再沉淀:
由于固体颗粒溶解,它们富集成分中的流体,特别是在溶解速度更快的附近。
相反,在与最小主压应力(3)垂直的晶界附近几乎不发生溶解。
溶解速率的差异导致流体内的化学浓度梯度(实质),导致溶解成分从溶解位点扩散到较低压缩应力的位置。
比较常见的是难熔物质的两侧,周围的易溶物被溶解迁移到难熔矿物的低应力区沉淀,形成以难溶物为核晶,以易溶物为阴影的压力影构造。
Conditionofdissolutioncreep:
IntergranularfluidLowdifferentialstressLowtomoderatetemperatureSmallgrainsizefavordissolution:
Strainrateisinverselyproportionaltothecubeofthegrainsize;
hence,grain-sizereductionbydissolutionleadstoaquickeningofthepaceofdissolution,atypeofstrainsoftening.6.IntracrystallineDeformation晶内缺陷Crystalscandeforminternallywithoutbrittlefracturingbymovementofso-calledlatticedefects,aprocessknownasintracrystallinedeformationLatticedefects:
Pointdefect,linedefectsandplanardefectDislocationglide位错滑动位错滑动LineardefectintheCrystalBurgersVector:
AdislocationischaracterizedbyaBurgersvectorwhichindicatesthedirectionandminimumamountoflatticedisplacementcausedbythedislocation.通常将柏氏矢量称为位错强度,位错的许多性质如位错的能量,所受的力,应力场,位错反应等均与其有关。
它也表示出晶体滑移时原子移动的大小和方向。
位错可定义为柏氏矢量不为零的晶体缺陷,它具有连续性,不能中断于晶体内部。
其存在形态可形成一个闭合的位错环,或连接于其他位错,或终止在晶界,或露头于晶体表面。
边缘位错和螺旋位错可以互相连接成位错环Dislocationglideeasieronspecificslip-systemsdependingonP,T,fH2O,etcDislocationClimb位错攀移位错攀移Migrationofvacanciestothedislocationplanecancausetheclimbofthedislocation杂质35Theshapeofacrystalcannotbepermanentlychangedbyjustsqueezingit;
thedistancebetweenlatticepointscanonlybechangedbyaverysmallamount,leadingtoelasticdeformation.Ifstressisreleased,theoriginalshapeisrecovered.Apermanentchangeinshapecanonlybeachievedbyachangeintherelativepositionsofmoleculesoratoms.Thishappensbymovementoflat-ticedefectsthroughacrystalintheprocessofintracrys-tallinedeformation(Poirier1985;
Hull1975).ConsiderthevacanciesinFig.3.12.Ifneighbour-ingatomsoccupythevacancysites,vacanciesaremovingthroughthecrystalandthecrystalmaychangeshapepermanently(Videos3.12a,3.12b).Movingdislocationscanalsocauserelativedisplacementofpartsofacrystallattice.Figure3.15a(Videos3.11,3.15a)showshowmovementofadislocationdis-placespartsofcrystalswithoutactuallyseparatingonepartofthecrystalfromtheother.Dislocationscanbegeneratedinacrystalatso-calleddislocationsources.AnexampleisaFrank-Readsource(Fig.3.15b,Video3.15b).Ductiledeformationofrocksistoalargeextentachievedthroughthemigrationofdislocationsandva-cancies.Latticedefectscancausesignificantstrainincrys-talsonlyifnewdefectsarecontinuouslycreated;
thiscanhappenatdislocationsourcesandvacancysourceswithinthecrystaloratcrystalboundaries.Intracrystallinedeformationbyglideofdislocationsaloneisknownasdislocationglide.Dislocationshaveadistinctorientationwithrespecttothecrystallatticeandcanmoveonlyinspecificcrystallographicplanesanddirections(Fig.3.11d).Aspecificslipplanecoupledwithaslipdirec-tion(theBurgersvector)isknownasaslipsystem.Slipsys-tems(Box3.4)formineralsarenormallydeterminedbyTEM(Sect.10.2.5;
Fig.10.11).Inmostcommonrock-formingmin-eralssuchasquartz,feldspars,calciteandolivine,severalslipsystemsofdifferentorientationcanbeactive(Sect.3.12).ThetypeofslipsystemthatwillbeactiveinacrystaldependsFiFigg.33.1155.aaDeformationofacrystalbymovementofanedgedislocation;
thetophalfofthecrystalistranslatedoveronelatticeunittotherightasaresultofthepassageofasingledislocationfromlefttoright.Viewnormaltotheedgedislocation.OnelatticeplaneismarkedtoshowtherelativedisplacementoftheupperpartofthecrystalwithrespecttothelowerpartbbOperationofaFrank-Readdislocationsource.Ashortdislocationsegmentbetweentwoinclusionsinacrystal,withBurgersvectorintheplaneofthepaper,isdisplacedunderinfluenceofadifferentialstressinthecrystal.Thedislocationpropagatesintoakidneyshapeuntiltheendsmeetandannihilate;
adisloca-tionloopasinFig.3.11disformed,andtheremainingdislocationsegmentcanmigrateagaintoformmoredislocationloopsFiFigg.33.1166.aaDislocationblockedbyanim-purityinthecrystal.bbMigrationofvacanciestothedislocationplanecancauseclimbofthedislocationawayfromtheob-struction.ccAfterclimb,thedis-locationisnolongerblockedandcanpasstheobstruction3.4Intracr3.4IntracryystallinestallineDDeeformationformationDislocationCreep位错蠕变位错蠕变moderateTandstress蠕变creep:
在地质条件下,应变极其缓慢。
矿物中的位错有足够的时间顺序移动。
所以能在不增加应力的情况下使应变继续增加,这就是蠕变。
就像挪动很重的地毯。
应力保持一定,应变随时间不断增加的现象。
Dislocationcreep=DislocationGlide+DislocationClimb(当位错的增值引起的内应力增加(硬化)与由攀移等引起的内应力减小(恢复)之间达到动态平衡时,变形进入稳态蠕变阶段)三个阶段:
微应变阶段:
弹性应变塑性应变阶段稳态流动阶段:
应力不再增加。
结果是在矿物晶粒中产生了以位错阵列为边界的亚晶粒subgrain(而不是形成新晶粒)Unduloseextinction波状消光:
lowThighstressSubgrainboundaries亚晶界/Kink扭折:
highTlowstressSlip-System:
Aspecificslipplanecoupledwithaslipdirection(theBurgersvector)isknownasaslipsystem.Slip-system:
crystallographicdirectionandplaneinwhichthedislocationglide.DenominationusingMillerindices:
Directions:
hkl(or=allhklequivalentdirectionbysymmetry)Plane:
(hkl)(orhkl=allhklequivalentplanebysymmetry)CrystalPreferredOrientation