沉积岩第4章变质作用研究

1、第四章、第四章、变质作用研变质反应与成岩格变质变质相系和双变质变质岩原岩恢一、变质反应与成岩格一、变质反应与成岩格1、相律和相相律在一个封闭体系中，当变质反应达到平衡(StableMineraletamorphicEquilibriumMineralAtequilibrium,themineralogy(andthecom mineral) is determined by T, P, and Xitionof“Mineralparagenesis”referstosuchanequilibriumThePhasephaserule,asF=CThePhasephaserule,asF=C-+

2、dtosystemsatisthenumberofhesystem(相数Cisthenumberofcomponents:theminimumnumber of chemical constituents required to specify everyhesystem（独立组分数Fisthenumberofdegreesoffreedom:thenumberindependently variable (suchastemperature,preensiveparametersofere,theitioneachphase,度ThePhaseetamorphicConsiderThePha

3、seetamorphicConsiderthefollowingthreeC=onlyatspecificP-Tconditions of the invariant po(0.37GPaandTheP-Tphasediagramforthesystem Al2SiO5 calculatedusingtheprogram TWQ(Berman,1988,1990,1991).WidtphaseidtphaseF=C- f +2fThisisidtsmineralogicalphaseorsimplythemineralogicalphasea) =etamorphicTherockprobab

4、lyrepresentsanequilibriummineralThePhaseetamorphic Common with mineral texhibitsolid存在流体相，或存在固溶ThePhaseAerestingsituation,eastoneAerestingsituation,eastoneofsituationsmustberesponsible（有三种状态F Theleiscollectedfromalocationrightonunivariantreactioncurve(isogradorinvariantpo EquilibriumhasnotbeenThepha

5、serulesonlytosystemsatandtherecouldbeanynumberofmineralsifequilibriumisWedidntchoosethe#ofcomponents独立组分数限定错了相图相图(Phase2、变质反2、变质反基2、变质反2、变质反单成分相转变(Isochemicalphasetransformations如SiO2 or Al2SiO5 graphite- diamondorcalcite-aragonite(Thetransformationsdependontemperatureandopx+pl=grt+cpx+qz;re叶腊石=and+

6、qz+H2O上述所上述所有反应是一种理想化学反应，说明反应物与生成物之间的关系0.4GPa,0.4GPa,Kf+sill组合?qz具有具有固溶体矿物不连续反不连续反近乎一种突变变线（平衡）连续反3(Mg,Fe)2Al4Si5O18连续反3(Mg,Fe)2Al4Si5O18=堇青石榴子矽线石 石(Mg,Fe)5AlAlSi3O10(OH)+KAl2AlSiO10(OH)2 绿泥白云石黑云石连续反连续反在此反应堇青石的形成，绿泥石和黑云母不完全连续反定义：在连续反定义：在涉及固溶体的反应中，生成物的形成内连续反应或滑动反应D+G+F+H；D+G+F+H；A+C+E+F；。Continuousocc

7、urwhenF1,ContinuousoccurwhenF1,andreactantsandproductscoexistoveratemperatureSchematicisobaricrepresenting the metamorphicreaction Chl + Qtz Grt +equalibriuminafield with F=2.不同不同型反定（对反应的影。定（对反应的影。P-T-3、3、成岩格子和地质温压Petrogeneticgridand定义：由多个反应曲线或相图组合而成的P-T间的反应曲线网格图解成岩格3、3、成岩格子和地质温压3、3、成岩格子和地质温压成岩格子成岩格

8、子地质温压变质作用温压的确定方法Ky- grt- sill- kf-pl-bt- 矽线石片麻(1成岩格成岩格子确定平衡温压的优缺点优点：简单，快缺点：不够精确(结果是一个很大的范围(2)、地质(2)、地质温压原理：热力学平衡，平衡矿物为固溶体，反应物与G=0G0G=0G0 +RTG0 =-RTForreaction:2A+3B=C+K=(C.D )/(A .B A=XA. K=KD . K G=H dG= VdP- lnK=lnKD +lnK=-H0/RT+S0/RGarnet-BiotiteFeGarnet-BiotiteFe3Al2Si3O12+KMg3Si3AlO10(OH)2 =+ l

9、nK=K=KD = =Ferry & Spear lnKD =-H0/R.(1/T)+Ferry&SpearTheGarnetBiotitegeothermometer（实验标定Experimental results of Ferry and Spear (1978) on a Garnet-Biotite GeothermometerTKFerry&SpearTheGarnetBiotitegeothermometer（实验标定Experimental results of Ferry and Spear (1978) on a Garnet-Biotite GeothermometerT

10、KTGarnet-Garnet-lnKD =-2108/T(K)+GP,T =0=GP,T =0=0.1,298 -TS0.1,+PV+3ToC 52,0902.494PMPa 19.50612.943lnKDln HPV 1 TTheTheGarnet-BiotiteTheGASPP-T phase diagram showing the experimental results of Koziol and Newton(1988),TheGASPP-T phase diagram showing the experimental results of Koziol and Newton(1

11、988),andtheequilibrium curve for reaction. Open triangles indicate runs in which An grew, closed triangles indicate runs in which Grs + Ky + Qtz grew, and half-filled triangles indicate no significant reaction. The univariant equilibrium curve is a best-fitofthedatabrackets.line at 650oC is Koziol a

12、nd Newtons estimate of the reaction location based on reactions involvingzoisite.Theshadedareaistheyenvelope.KoziolandNewton(1988)Amer. Mineral., 73, 216-233TheGASPTheGASPP-T diagram contoured for equilibrium curves of various values of K for the GASPgeobarometerreaction:3An=Grs+2Ky+Qtz.FromSpear(19

13、93)不不同温度计和压力计的组不不同温度计和压力计的组bt-Ferrybt-Ferry&Spear(1978);Hodges&Spear(1982);Ganguly&(1984);Perchuketal.(1983);Indaresetal.cpx-opx,Wood&Banno(1973);Wells(1977);Bertrand&Mercier(1985); Brey & Kohler (1990)cpx-gt,Ellis&Green(1979);Harley(1984);kf-pl,StomerJr.(1975);Priceetal.gt-opx,Wood(1974);Nickel&Gre

14、en(1985);Harleygt-cpx-pl-qz,Newton&Perkinsgt-pl-AS-qz,Ghentetal(1976,gt-pl-bt-ms,Ghentetal(1981);Ashworth(1985);Hoisch必须必须存在这样的矿物组合；如gt-cpx-pl-矿物成分和岩石组合的限制，如Perchuk et 0.22XMgBt 0.83,gt:0.05XMgGt 0.77；如Brey&Kohler(1990)的二辉石温计只适用于橄榄岩体系，即具ol+opx+ cpx+gt (or sp)组合。计算步骤计算步骤矿物的成分分析(如电子探针分子结构式的计算，分配系数的确定优

15、点: 精确，误差小(50100; 缺点: 局限（要求严格），繁琐，花大4、P-T-t轨4、P-T-t轨ConsiderthecompletesetofT-Ptamay experience during a metamorphic cycle from burialtometamorphism(andorogeny)toupliftand，Suchacycleiscalleda-timepath,orP-T-tP-T-t轨迹P-T-t轨P-T-t轨迹的确矿物间的包含关系，交代特征，判断哪些利用具成分环带的矿物的核部到边缘的I.I.等温降等温降ChemicalChemicalzoningprof

16、ilesacrossagarnetfromtheTauernWindow.AfterSpearConventionalP-TdiagramConventionalP-Tdiagramreincreasesupward)showingthreeed “clockwise”T-tpathscomputedfromtheprofilesusingthemethodofSelverstoneetal.re-temperature-timere-temperature-timepathsbasedonheat-flows.Al2SiO5phasediagramandtwohypotheticaldehy

17、drationcurvesarePathis considered aPathis considered atypicalP-T-t path for an orogenic belt with crustal 在增厚的阶段，P迅速增加，而T升高缓慢P，T同时下降，由于隆升和剥蚀整个过程地温梯度发生很大变化这种模式被称为顺时针(clockwiseP-T-t轨SchematicP-T-tpathsforaSchematicP-T-tpathsforashallowmagmatismPathflow.Due to shallowThismaybean appropriate P- T-t path

18、 for PathP-T-t path见于高PathP-T-t path见于高级片麻P-T同时增加侵入活动结束变降温发生等P-T-tpathsbasedonaheat-flowfortypesofgranulitefacies温压并不一定同步升高或降低质作用中有很大变化；Pmax andTmax温压并不一定同步升高或降低质作用中有很大变化；Pmax andTmax 并不同时达到heusualcaseof“clockwise”P-T-tpaths,Pmax occursnTmax shouldrepresentumgradeatwhichequilibriumis“frozenin”andthe

19、metamorphicmineral assemblage is developed;“Metamorphicgrade”shouldrefertothetemperatureandpre at Tmax, because the grade is determined via reference to the equilibrium mineral assemblage;3.顺时针P-T轨迹的隆升-ThekyanitesillimanitetransitionThekyanitesillimanitetransitionisgenerallyconsideredaprogradecrosse

20、sthekyanitesillimanitetransition(asin1),but2temperatureisdecreasing.Thismayresultinonlyminorreplacementofkyanitesillimaniteduringsucharetrogrades二、变质带(metamorphiceBarrow(1893,二、变质带(metamorphiceBarrow(1893,在研究SEHighlandsScotland的加里东造山带Caledonianorogeny500 Ma)的Regional Metamorphism时建立的。Barrowstudiedth

21、epelitichisAndfoundtheareacouldbeoaseriesmetamorphiczones,eachbasedontheappearance of a new mineral as metamorphic grade increasedTheyarechlorite,biotite,garnet,staurolite,kyanite and sillimanite zones.map of the map of the showing the zones oftdevelop with grade. From Gillen(1982)ThesequenceofThese

22、quenceofzonesnowrecognized,andtypicalmineralassemblageineach,Chloritezone.Peliticrocksareslatesorphyllitesandtypically contain chlorite, muscovite, quartz and albiteBiotitezone. Slatesgivewaytophyllitesandschists,with biotite, chlorite, muscovite, quartz, and albiteGarnetzone.Schistswithconspicuousr

23、edalmandinegarnet, usually with biotite, chlorite, muscovite, quartz, and albite or Staurolitezone.Schistswithstaurolite,biotite,muscovite, quartz, garnet, and plagioclase. Some chlorite may persistKyanitezone.Schistswithkyanite,biotite,muscovite,quartz, plagioclase, and usually garnet and staurolit

24、e.Sillimanitezone.Schistsandgneisseswithsillimanite,biotite, muscovite, quartz, plagioclase, garnet, and perhaps staurolite. Some kyanite may also be present (although kyanite and sillimanite are both polymorphs of Al2SiO5)=Barrovianzones系）（The P-T conditions referred toasBarrovian-type 等变线(Isograd)

25、tthe zones (a line in the field of constant metamorphicgrade)To一个To一个等变线代表一个特征变质矿物的第一次出现Anisogradhisclassicalsense)representsappearanceofaparticularmetamorphicindex通过这个等变线，意味着进入了这个变质带(Whenonecrossesanisograd,suchasthebiotiteisograd, one enters the biotite zone）相同原岩的每个变质带形成于相同条件（等物等变线是以一个特征矿物出现为标志，并不

26、涉及消AtypicalBarrovian-typeAtypicalBarrovian-typemetamorphicfieldgradientandaseriesmetamorphicP-T-tpathsforrocksfoundtheAb-Ab-ab+chl+epqzcc,ab+act+ep+chlqz阳起石出现=黑云母出Ab-ab+hb(蓝绿色阳起石普通角闪石主要是2Al=Si+(Mg, Fe)置Pl-Two-Hb+alm+5qz7opx+pl+H2OAvariationheareaAvariationheareajusttothenorthhendBuchanHerethepelitic

27、itionsarebutthesequenceofisogradsThestabilityfieldThestabilityfieldofandalusiteoccursatresn0.37GPa(10km),whilekyaniteisogradisabovethisContact Metamorphism and FormationContact Metamorphism and FormationatCrestmore,CA,Anidealizedcross-sectionthroughtheIdealizedN-S cross section (not to scale) throug

28、h the and the aureole at CA. From 三、变质相(Metamorphic三、变质相(MetamorphicEskola(1915)developedtheconceptof metamorphic facies:Definition:变质相就是一个特定的变质温压条三、变质相(Metamorphic变质三、变质相(Metamorphic变质相概念的两个基本特征是相似于沉积相的概念，即不同的沉积环境等同于不同的变质环境三、变质相(MetamorphicEskola(1920)ed5original三、变质相(MetamorphicEskola(1920)ed5orig

29、inalhibolite角闪岩Hornfels角透长岩e 榴辉岩EclogiteMetamorphicInhisfinalaccount,EskolaMetamorphicInhisfinalaccount,Eskola(1939)麻粒岩相Granulite hibolite绿帘角闪岩蓝片岩相Glaucophane-Hornfelsfacieschangedtothepyroxenehornfels EacheasilydefinedonthebasisoftaficHisfacies,andhisestimateoftheirrerelationshipsareshownMetamorphi

30、cThemetamorphicfaciesMetamorphicThemetamorphicfaciesedbyEskolaandtheirtemperature-rerelationships.AfterEskolaFormation of ZeolitesSchistMetamorphic从那以后，sMetamorphic从那以后，s在研究New Zealan的埋深变质时增加了沸石相(Zeolite)和葡萄石石；Fyfe et al(1958)也提出（增加）了钠长-绿帘角岩相dote hornfels)和角闪石角(Hornblende hornfels)现在被普遍接受的变质相有11个，包括

31、4个触变质作用中的和7个区域变质作用中的MetamorphicMetamorphicT-P diagram showing the acceptedlimits of the various Boundaries are approximate and gradational. The “typical” or geothermisfrom Brown and Mussett (1993).MetamorphicThedefinitivemineralassemblages facies (for mafic rocks).tcharacterizeTable25-1.DefinitiveMi

32、neralAssemblagesofMetamorphicDefinitiveMineralaficPrehnite-prehnite+pumpellyite(+chlorite+chlorite+albitedote(orMetamorphicThedefinitivemineralassemblages facies (for mafic rocks).tcharacterizeTable25-1.DefinitiveMineralAssemblagesofMetamorphicDefinitiveMineralaficPrehnite-prehnite+pumpellyite(+chlo

33、rite+chlorite+albitedote(orzoisite)+quartz?hornblende+plagioclase(oligoclase-andesine)?orthopyroxene(+clinopyrixene+plagioclase?glaucophane+lawsonitedote(+albite?pyropegarnet+omphaciticpyroxene(?Mineral afic rocks of the facies of contact Contactmorphism do not differ substantially t of the regional

34、 facies at After Spear 可以把变质相分成4组高可以把变质相分成4组高压相（FaciesofhighTheblueschistandeclogiteBlueschistfacieslower-temperatureandlowT/P gradients subduction zones.因为eclogite可以稳定于正常的地温条件下，（Becauseeclogitesarestableundernormalconditions,theymaydevelopwherevermafichedeepcrustormantle(crustalchambersdikes,sub-cr

35、ustalmagmaticlates,subductedtisotheFaciesofmediumre中压相ranuliteFaciesofmediumre中压相ranuliteFaciesoflowre低压相Thedotehornfels,hornblendehornfels,pyroxene hornfels facies: contact metamorphic terranes and regional terranes with very high geothermalgradients.Thesanidinitefaciesisrare and limited to xenolit

36、hs in basic magmasFaciesoflowgrades低级相Thezeoliteandprehnite-pumpellyitefaciesarethus notalwaysrepresented,andthegreenschistfaciesisthelowestgradeanyregional变质亚变质亚巴罗变质带Chlzone=巴罗变质带Chlzone=lowgreenschistBiGtStKy =lowgreenschist=highgreenschist=hibolitehibolite facies hiboliteSillzone=基性变质带：Ab-chllowgreenschistAb-act=highgreenschistAb-=hibolitePl-=hibolite2-pyroxene=granulite四、变质相系(facies四、变质相系(facies(Miyashiro1963FigureFigure21-1.Metamorphicfieldgradients(estimatedP-Tconditionsalongsurfacetraversesdirectlyupmetamorphicgrade) for