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1、变质作用期次及温压条件变质作用期次及温压条件的确定的确定2021/6/161一、成分共生图解和组分分析1.矿物组合及其确定标志在共生分析中，把一定化学成分岩石达到化学平衡 时 的 矿 物 成 分 称 为 矿矿 物物 组组 合合 （ mineralassemblage） 或 矿矿 物物 共共 生生 组组 合合 （ mineralparagenesis）(P311)。2021/6/162确定矿物共生组合的主要标准确定矿物共生组合的主要标准（1）一个矿物共生组合中各种矿物相互接触；（2）一个矿物共生组合的各矿物，相互间无反应和交代现象；（3）一个矿物共生组合中，同种矿物的化学成分及光性特征应相近。如
2、有环带，则其边部化学成分及光性特征近似；（4）一个矿物共生组合中的一对矿物之间元素的分配符合Nernst分配定律，即各处元素的分配系数近相等；（5）矿物共生组合中矿物共生关系应符合矿物相律，即矿物相数不超过惰性组分数。2021/6/163共生与共存共生与共存共生与共存是两个完全不同的概念。共存：具有不同物理特征和/或化学特征的相，同时间、空间呈集合体存在，相之间的关系不一定服从热力学定律。共生：同时空呈集合体存在的相，在相同物理化学条件下形成，并达到热力学平衡。体系的内能最低。2021/6/164变质相与变质相系列变质相与变质相系列变质相：变质相：Eskola（ 1920 ）：一个变质相是指类
3、似的温度、压力条件下达到化学平衡的所有岩石总和(不论其结晶方式），一个变质相内部，随着岩石总体化学成分的改变，其矿物组合作有规律的改变。Fyfe and Turner（1966）：一个变质相是指一定的温度、压力区间内的一整套变质矿物共生组合，它们在时间上、空间上反复出现并紧密地伴生在一起，一个变质相内部其矿物组合与岩石总体化学成分之间有着固定的、因而也是可以预测的对应关系。2021/6/165Turner1981年提出变质相的分类接触变质相：（以温度增高为序）钠长绿帘角岩相，普通角闪石角岩相，辉石角岩相，透长石相。区域变质相:沸石相，葡萄石绿纤石相，绿片岩相，蓝闪石硬柱石相，绿帘角闪岩相，角闪
4、岩相，麻粒岩相，榴辉岩相2021/6/1662021/6/167接触变质岩相1. 钠长绿帘角岩相（AEH）：低温,温度约为300-400。C，压力0.1-0.4GPa,特征矿物组合：钠长石+绿帘石+透闪石或阳起石。没有钙质斜长石和铝质角闪石。铁质堇青石和黑云母出现于低温部分，红柱石出现温度稍高，有时又叶蜡石。特征岩石是斑点板岩。2. 普通角闪石角岩相（HH）：中温,温度约400-650。C，压力为0.1-0.3GPa,特征矿物组合：斜长石+普通角闪石,可以有透辉石，而没有斜方辉石。变质泥质岩与长英质岩石中红柱石，堇青石不与钾长石共生。2021/6/1683. 辉石角岩相（PH）: 高温,温度约
5、650-800。C，压力不超过0.2GPa,夕线石，正长石，紫苏辉石或硅灰石为标志矿物,白云母+石英不稳定。红柱石，堇青石，夕线石开始与正长石稳定共存。特征矿物组合:斜长石+透辉石+紫苏辉石4. 透长石相（S）: 极高温温度约800-1100。C，压力极低，0.02-0.08GPa,黄长石，钙镁橄榄石，斜硅钙石和透长石等为特征矿物,特征矿物组合:斜长石+普通辉石+易变辉石。2021/6/169FaciesoflowpressureAlbite-epidotehornfels,hornblendehornfels,andAlbite-epidotehornfels,hornblendehornf
6、els,andpyroxenehornfelsfacies:contactmetamorphicpyroxenehornfelsfacies:contactmetamorphicterranesandregionalterraneswithveryhighterranesandregionalterraneswithveryhighgeothermalgradient.geothermalgradient.MetamorphicFaciesFFSanidinitefaciesisSanidinitefaciesisrare-limitedtorare-limitedtoxenolithsinb
7、asicxenolithsinbasicmagmasandthemagmasandtheinnermostportionsofinnermostportionsofsomecontactaureolessomecontactaureolesadjacenttohotbasicadjacenttohotbasicintrusivesintrusives2021/6/1610区域变质岩相1.沸石相(Z或ZE)：很低温温度约200-300。C，压力为0.2-0.3GPa。特征矿物组合：钠长石+浊沸石+绿泥石+葡萄石石英。2.葡萄石-绿纤石相（PP）：很低温温度约360-400。C，压力为0.25-0
8、.35GPa。特征矿物组合：钠长石+葡萄石+绿纤石+绿泥石多硅白云母石英。3.蓝闪石-硬柱石片岩相（GL）：很低温温度200-450。C，压力0.3-0.8GPa.特征矿物组合：（低压）硬柱石+钠长石+绿泥石；（高压）蓝闪石+硬柱石+硬玉质辉石+石英。是一个范围很宽的低温高压变质相，有时含有文石，完全不含黑云母。压力有时可达到1GPa或更高。2021/6/16114. 绿片岩相(GS）: 低温,温度约400-500。C，压力0.3-0.8GPa。特征矿物组合：（泥质岩石）钠长石+绿帘石+白云母+绿泥石+石英 （基性岩石）钠长石+绿帘石+绿泥石+阳起石；高温部分出现黑云母，高压部分出现黑硬绿泥石
9、，硬绿泥石和铁铝榴石。叶蜡石和硬绿泥石等不与钾长石共生。5. 绿帘角闪岩相(EA): 低温,特征矿物组合：钠长石+绿帘石+普通角闪石（+铁铝榴石）.低压条件下，钙质斜长石的形成温度低于普通角闪石时，便不能生成绿帘角闪岩相的共生。而形成斜长阳起石相。2021/6/16126. 角闪岩相(A或AM): 中温温度约500-700。C，压力0.3-0.8GPa,普通角闪石和斜长石的共生是本相的标志,可以有透辉石没有斜方辉石。泥质岩中除了石英，白云母和黑云母外，低压相系含红柱石，堇青石和夕线石，中压相系含十字石，蓝晶石和铁铝榴石。高温部分夕线石，铁铝榴石开始与正长石稳定共生。7. 麻粒岩相(G): 高温
10、温度700-900。C，压力0.3-1.2GPa,出现斜方辉石为标志岩石主要由无水矿物所组成，少量黑云母和普通角闪石一般是富Ti的变种。8. 榴辉岩相(E): 高压温度300-900。C，压力大于1GPa,特征矿物组合：绿辉石+石榴子石不含长石。一般呈不大的块体在其它岩石中作为包体。温度范围很宽，压力极大。2021/6/1613变质相系1.接触变质相系:dT/dP=80,硅灰石，堇青石，红柱石，（基本不含硅线石，不含十字石）2.低压区域变质相系, dT/dP=80-40,红柱石，硅线石，堇青石，（不含硅灰石，蓝晶石，基本不含十字石）3.中压区域变质相系, dT/dP=20-40,浊沸石，蓝晶石
11、，硅线石，十字石（不含红柱石，堇青石，蓝闪石，硬玉）4.高压区域变质相系, dT/dP=20-5, 硬柱石，蓝晶石，蓝闪石，硬玉（不含硅线石，浊沸石）2021/6/16142021/6/1615Fig. Temperature-Fig. Temperature-pressure diagram pressure diagram showing the three showing the three major types of major types of metamorphic metamorphic facies series facies series proposed by propo
12、sed by Miyashiro (1973, Miyashiro (1973, 1994). 1994). Winter Winter (2001) An (2001) An Introduction to Introduction to Igneous and Igneous and Metamorphic Metamorphic Petrology. Petrology. Prentice Hall.Prentice Hall.2021/6/1616变质相与变质相系列变质相与变质相系列变质相系列：变质相系列：变质相系列：变质相系列： 同一地区通常不止一个变质相，可以由许多不同的变质相组成
13、，构成变质相的系列；并且不同地区甚至同一地区不同地段变质相系列不一样。最著名的是本世纪50年代末期，日本地质学家都城秋穗在研究日本三波川带 和领家带时，发现同一地区可以存在两个不同的变质相组合。他指出，在变质带中，从低温在变质带中，从低温在变质带中，从低温在变质带中，从低温向高温的的变化可以定义为一个相系列，或者称作变向高温的的变化可以定义为一个相系列，或者称作变向高温的的变化可以定义为一个相系列，或者称作变向高温的的变化可以定义为一个相系列，或者称作变质相系质相系质相系质相系。并且他认为每一种特定的变质相系列都反映每一种特定的变质相系列都反映每一种特定的变质相系列都反映每一种特定的变质相系列
14、都反映了各自的特定地热梯度类型和所经历的事件和演化进了各自的特定地热梯度类型和所经历的事件和演化进了各自的特定地热梯度类型和所经历的事件和演化进了各自的特定地热梯度类型和所经历的事件和演化进程程程程，这就是变质相系列的实质。2021/6/1617变质相与变质相系列变质相与变质相系列 (1)(1)(1)(1)大体上的等物大体上的等物大体上的等物大体上的等物理系，标志是一系列理系，标志是一系列理系，标志是一系列理系，标志是一系列特征的矿物共生组合特征的矿物共生组合特征的矿物共生组合特征的矿物共生组合 (2)(2)(2)(2)变质相是由变质相是由变质相是由变质相是由变质反应来标定界线变质反应来标定界
15、线变质反应来标定界线变质反应来标定界线 (3)(3)(3)(3)时间上、空时间上、空时间上、空时间上、空间上反复出现是指同间上反复出现是指同间上反复出现是指同间上反复出现是指同一变质相的岩石在不一变质相的岩石在不一变质相的岩石在不一变质相的岩石在不同时间，不同地区经同时间，不同地区经同时间，不同地区经同时间，不同地区经常重复出现，并伴随常重复出现，并伴随常重复出现，并伴随常重复出现，并伴随在一起。在一起。在一起。在一起。2021/6/16182021/6/16192021/6/16202021/6/16212)FaciesofmediumpressureMostmetamorphicrocks
16、nowexposedbelongtotheMostmetamorphicrocksnowexposedbelongtothegreenschistgreenschist, ,amphiboliteamphibolite,or,orgranulitegranulitefaciesfaciesTheThegreenschistgreenschistandandamphiboliteamphibolitefaciesconformtothefaciesconformtothe“typical”geothermal“typical”geothermal gradientgradientMetamorp
17、hicFacies2021/6/1622MetamorphicFaciesFFZeoliteZeoliteandandprehnite-prehnite-pumpellyitepumpellyitefaciesarefaciesarethusnotalwaysthusnotalwaysrepresented,andtherepresented,andthegreenschistgreenschistfaciesisfaciesisthelowestgradethelowestgradedevelopedinmanydevelopedinmanyregionalterranesregionalt
18、erranes4)FaciesoflowgradesFFRocksoftenfailtorecrystallizethoroughlyatverylowRocksoftenfailtorecrystallizethoroughlyatverylowgrades,andequilibriumisnotalwaysattainedgrades,andequilibriumisnotalwaysattained2021/6/1623MetamorphicP-T-tpathsmaybeaddressedby:1)Observingpartialoverprintsofonemineralassembl
19、ageuponanotherTherelictmineralsmayindicateaportionofeithertheprogradeorretrogradepath(orboth)dependinguponwhentheywerecreatedPressure-Temperature-Time(P-T-t)Paths2021/6/1624MetamorphicP-T-tpathsmaybeaddressedby:2)Applygeothermometersandgeobarometerstothecorevs.rimcompositionsofchemicallyzonedmineral
20、stodocumentthechangingP-TconditionsexperiencedbyarockduringtheirgrowthPressure-Temperature-Time(P-T-t)Paths2021/6/1625Chemical zoning profiles across a garnet from the Tauern Window. After Spear (1989) Chemical zoning profiles across a garnet from the Tauern Window. After Spear (1989) 2021/6/1626Fig
21、. Conventional P-T diagram (pressure increases upward) showing three modeled “clockwise” P-T-t paths computed from the profiles using the method of Selverstone et al. (1984) J. Petrol., 25, 501-531 and Spear (1989). After Spear (1989) Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths.
22、 Mineral. Soc. Amer. Monograph 1.2021/6/1627MetamorphicP-T-tpathsmaybeaddressedby:Evenunderthebestofcircumstances(1)overprintsand(2)geothermobarometrycanusuallydocumentonlyasmallportionofthefullP-T-tpath3)Wethusrelyon“forward”heat-flowmodelsforvarioustectonicregimestocomputemorecompleteP-T-tpaths,an
23、devaluatethembycomparisonwiththeresultsofthebackwardmethodsPressure-Temperature-Time(P-T-t)Paths2021/6/1628 Classicview:regionalmetamorphismisaresultofdeepburialorClassicview:regionalmetamorphismisaresultofdeepburialorintrusionofhotmagmasintrusionofhotmagmas Platetectonics:regionalmetamorphismisares
24、ultofcrustalPlatetectonics:regionalmetamorphismisaresultofcrustalthickeningandheatinputduringorogenyatconvergentplatethickeningandheatinputduringorogenyatconvergentplateboundaries(notsimpleburial)boundaries(notsimpleburial) Heat-flowmodelshavebeendevelopedforvariousregimes,Heat-flowmodelshavebeendev
25、elopedforvariousregimes,includingburial,progressivethruststacking,crustaldoublingbyincludingburial,progressivethruststacking,crustaldoublingbycontinentalcollision,andtheeffectsofcrustalanatexisandmagmacontinentalcollision,andtheeffectsofcrustalanatexisandmagmamigrationmigration Higherthanthenormalhe
26、atflowisrequiredfortypicalHigherthanthenormalheatflowisrequiredfortypicalgreenschist-amphibolitemediumP/Tfaciesseriesgreenschist-amphibolitemediumP/Tfaciesseries UpliftanderosionhasafundamentaleffectonthegeothermandUpliftanderosionhasafundamentaleffectonthegeothermandmustbeconsideredinanycompletemod
27、elofmetamorphismmustbeconsideredinanycompletemodelofmetamorphismPressure-Temperature-Time(P-T-t)Paths2021/6/1629Fig. Schematic pressure-temperature-time paths based on heat-flow models. The Al2SiO5 phase diagram and two hypothetical dehydration curves are included. Facies boundaries, and facies seri
28、es from Figs. 25-2 and 25-3. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.2021/6/1630Broadagreementbetweentheforward(model)andbackward(geothermobarometry)techniquesregardingP-T-tpathsThegeneralformofapathsuchas(a)thereforeprobablyrepresentsatypicalrockduringoroge
29、nyandregionalmetamorphismPressure-Temperature-Time(P-T-t)Paths2021/6/16311.Contrarytotheclassicaltreatmentofmetamorphism,temperatureandpressuredonotbothincreaseinunisonasasingleunified“metamorphicgrade.”TheirrelativemagnitudesvaryconsiderablyduringtheprocessofmetamorphismPressure-Temperature-Time(P-
30、T-t)Paths2021/6/16322. Pmax and Tmax do not occur at the same time In the usual “clockwise” P-T-t paths, P In the usual “clockwise” P-T-t paths, Pmaxmax occurs occurs much earlier than Tmuch earlier than Tmaxmax. . T Tmaxmax should represent the maximum grade at which should represent the maximum gr
31、ade at which chemical equilibrium is “frozen in” and the chemical equilibrium is “frozen in” and the metamorphic mineral assemblage is developedmetamorphic mineral assemblage is developedThis occurs at a pressure well below PThis occurs at a pressure well below Pmaxmax, which is , which is uncertain
32、 because a mineral geobarometer should uncertain because a mineral geobarometer should record the pressure of Trecord the pressure of Tmaxmax“Metamorphic grade” should refer to the “Metamorphic grade” should refer to the temperature and pressure at Ttemperature and pressure at Tmaxmax, because the ,
33、 because the grade is determined via reference to the equilibrium grade is determined via reference to the equilibrium mineral assemblagemineral assemblagePressure-Temperature-Time(P-T-t)Paths2021/6/16333.Somevariationsonthecooling-upliftportionofthe3.Somevariationsonthecooling-upliftportionofthe“cl
34、ockwise”path(a)indicatesomesurprising“clockwise”path(a)indicatesomesurprisingcircumstancescircumstancesForexample,thekyaniteForexample,thekyanitesillimanitetransitionissillimanitetransitionisgenerallyconsideredaprogradetransition(asinpathgenerallyconsideredaprogradetransition(asinpatha a1 1),butpath
35、a),butpatha2 2crossesthekyanitecrossesthekyanitesillimanitesillimanitetransitionastemperatureistransitionastemperatureisdecreasing.decreasing.ThismayresultThismayresultinonlyminorreplacementofkyanitebysillimaniteinonlyminorreplacementofkyanitebysillimaniteduringsucharetrogradeprocessduringsucharetro
36、gradeprocessPressure-Temperature-Time(P-T-t)Paths2021/6/1634Fig. 25-12a.Fig. 25-12a. Schematic pressure-temperature-time paths based on a Schematic pressure-temperature-time paths based on a crustal thickeningcrustal thickening heat-flow model. The Al heat-flow model. The Al2 2SiOSiO5 5 phase diagra
37、m and two hypothetical dehydration curves are included. Facies boundaries, and facies series from Figs. phase diagram and two hypothetical dehydration curves are included. Facies boundaries, and facies series from Figs. 25-2 and 25-3. 25-2 and 25-3. Winter (2001) An Introduction to Igneous and Metam
38、orphic Petrology. Prentice Hall.Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.2021/6/1635Fig. 25-14.Fig. 25-14. A typical Barrovian-type metamorphic field gradient and a series of metamorphic P-T-t paths for rocks A typical Barrovian-type metamorphic field gradien
39、t and a series of metamorphic P-T-t paths for rocks found along that gradient in the field.found along that gradient in the field. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Hall.2021/
40、6/1636一、变质岩原岩恢复1.变质岩原岩恢复的一般原则a.变余特征优先原则b.岩套类比的原则c.等化学的原则d.惰性组分的原则e.相关性和趋势性原则2021/6/1637变余结构、构造（沉积岩）变余结构、构造（沉积岩）2021/6/1638变余斑状结构（a）和变余砂状结构（b）a.绿泥片岩，原岩中辉石斑晶为绿泥石交代呈假象；b.变质含砾石石英杂砂岩，碎屑为石英和石英岩，胶结物已变为细小的绢云母、黑云母和石英。2021/6/1639变质石英砂岩，辽宁。磨圆的石英颗粒之间分布的石英变质石英砂岩，辽宁。磨圆的石英颗粒之间分布的石英粘土已经变质为绢云母。粘土已经变质为绢云母。2021/6/1640变余结构、构造（火成岩）变余结构、构造（火成岩）2021/6/1641变余斑状结构（a）和变余砂状结构（b）a.绿泥片岩，原岩中辉石斑晶为绿泥石交代呈假象；b.变质含砾石石英杂砂岩，碎屑为石英和石英岩，胶结物已变为细小的绢云母、黑云母和石英。2021/6/1642B.岩石化学、地球化学和副矿物1.岩石化学a.K2ONa2Ob.图解法2.地球化学3.副矿物a.碎屑副矿物的有无和含量b.副矿物晶形及颜色2021/6/1643 结束语结束语若有不当之处，请指正，谢谢！若有不当之处，请指正，谢谢！
