地质学殷鸿福59章chapter7metamorphic rocks

Chapter7.Metamorphismandmetamorphicrocks1Metamorphismanditscontrollingfactors2Typesofmetamorphism3somecommonmetamorphicrocks7.1.metamorphismanditscontrollingfactorsA.Metamorphism变质作用

istheprocessinwhichconditionswithintheEarthalterthemineralcontentandstructureofsolidrockwithoutmeltingit.RocksthathavebeenalteredfrompreviouslyexistingrocksbymetamorphismaremetamorphicrocksB.factorscontrolingmetamorphism（1）temperature（2）Pressure（3）chemicalchangebyfluids（1）Temperature温度Changesintemperaturewillresultinchangestothemineralsorstructureoftherock.

Mineralarestablewhenthetemperatureisneitherhigherorlowerofthestability在一定的温度范围内矿物稳定Mineralsexposedtotemperaturesoutsideoftheirstabilityfieldwillchangeortrytochangetoastableconfiguration.

矿物暴露在矿物稳定温度范围之外时，矿物将改变自身，力图变得稳定。

Thetemperatureofmetamorphismhastwolimits:

Lowerlimitofmetamorphism-200°C

Upperlimitvariesbetween700-1200°C

（2）PressureChangesinpressurewillchangethecrystallinestructureofmineralsandthestructureoftherock.压力的改变会改变矿物的晶体结构和岩石的构造

Mineralsarestableundergiventemperatureconditions-theyarealsostableundercertainpressureconditions.

(3)ChemicalchangeDuringmetamorphism,waterisoftenpresent-hydrothermalfluids.变质过程中，水总是存在。

Hydrothermalfluidishotwater,plusotherchemicalsandgases.热水流体可以：

Thesefluidscandooneoftwothings:

1)removechemicalsfromtherock,thuschangingtheoverallchemistryoftherock.

2)addchemicalstoarock,thuschangingthechemistrytherock.

Achangeinchemistrywillresultinnewminerals.

Changethemineralsandtherockalsochanges.7.2TypesofmetamorphismTherearefourmaintypesofmetamorphism:contactmetamorphism接触变质作用regionalmetamorphism区域变质作用dynamicorfaultmetamorphism动力变质作用ComparisonbetweentypesofmetamorphismdistributionControllingfactorWaysofmetamorphismDynamicFaultzonesDirectionalforcedeformationContactContactzonebetweenaplutonanditscountryrockTemperatureandconfiningpressureMetamorphiccrystallizationRegionalAnywherewithinthelithosphereCombinationoftemperature,pressureandchemicallyactivefluidsMetamorphiccrystallizationanddeformation7.3Metamorphicrockssometypesofmetamorphicrockscanbeproducedfromanumberofdifferentparentrocks,therefore

metamorphicrocksaredistinguishedaccordingtoitsappearanceandtheconditionsthatformeditratherthanitscomposition.FoliationofmetamorphicrocksFoliatedTexture-面理构造：foliationisadistinctplanarcharacterwhichresultsfromdirectedpressure.

-mineralsshowapreferredorientationoralignment：1)

Slatycleavage板状构造（板理）

-veryfinefoliation

2)

Phylliticfoliation千枚状构造（千枚理）-veryfinefoliation，sheenfoliationplane

2)

Schistosity片状构造（片理）-mediumscalefoliation

3)

Gneissicbanding片麻状构造-alternatingbandsoflightanddarkcoloredminerals

Non-FoliatedTexture

-非定向构造（无面理）nopreferredorientationoftheminerals变质岩的常见面理1板状构造——变质程度较低的低级变质岩，沿面理容易裂开形成平整光滑但是无光泽的板片2千枚状构造——由非常细小的片状硅酸盐定向排列形成，容易裂开，但是表面不如板状构造平整，存在强烈的丝绢光泽3片状构造——由肉眼可见的片状、板状或柱状矿物排列而成，裂开面凹凸不平4片麻状构造——肉眼可见的深色和浅色、片状板状和许多粒状矿物间隔定向排列而成，片状和板状柱状矿物在岩石中呈现断续的定向排列。Foliatedmetamorphicrocks有面理的变质岩板岩Slate：Lowgrade(lowTandP),低级的变质岩，具板理，矿物微小不能分辨。slatycleavage,mineralsaretoosmalltosee，原岩泥岩或页岩shale,

mudstone.千枚岩Phyllite：Lowgrade,slatycleavage具千枚状构造,slightlylargercrystalsthanslate-stilltoosmalltosee,appearanceshowsaslightsheen有丝绢光泽，原岩泥岩或板岩片岩Schist

-Mediumgrade(moderateTandP),细粒，schistosity具有片理,platymineralsdominate(micas)片状矿物很多（云母），原岩细粒岩浆岩板岩千枚岩

片麻岩Gneiss：Highgrade(highTandP),粗粒、具有片麻状构造,原岩是片岩或粗粒的侵入岩SchistGneissNon-FoliatedMetamorphicRockTypes

石英岩Quartzite

-finetomediuminterlockingquartzgrains,ParentRock=

sandstone.

大理岩Marble

-finetomediuminterlockingcalcitecrystals,ParentRock=

limestone.

变质岩小结原先存在的岩石，在温度、压力和化学活动性流体的作用下变为新的岩石的过程称为变质作用。变质作用的方式有重结晶、变质结晶、变质分异、交代、变形、碎裂等变质作用的影响因素有，温度、压力和活动性流体变质作用根据其分布范围，作用方式和影响因素不同可以分为：接触变质，区域变质，动力变质，混合岩化等多种类型。变质岩是变质作用形成的岩石。变质岩的矿物成分复杂，含有很多特有的矿物；变质岩具有独特的变晶结构和面理构造，常见的面理有片理、千枚理、板理、片麻理等。Labforchapter6&7:RocksMainpurposeBefamiliarwithrockidentificationContents（玄武岩）basalt（辉长岩）gabbro （流纹岩）rhyolite （花岗岩）granite（安山岩）andesite（闪长岩）dioriteSlate,schist,gneissMudrock,sandstone,limestone,chertIdentificationofrocksTypeofrockcolorStructuresandtexturesSizeofparticlesclassificationMineralcompositionGabbro(辉长岩）grayunifiedCoarsegrainPyroxene,feldsparBasalt（玄武岩）GraybrownbubblesporphiryticDiorite（闪长岩）Gray-blackUnifiedcoarsegrainedHornblende,feldsparAndesite安山岩Green-grayporphiryticGranite花岗岩Pink-grayUnifiedCoarsegrainedQuartz,K-feldsparRhyolite流纹岩Pink-grayFlowingstructuresSlate板岩Deep-brownFoliationSchist片岩Green-black