單擊以編輯母版標題樣式,單擊以編輯母版文本樣式,第二級,第三級,第四級,第五級,*,變質作用期次及溫壓條件的確定,一、成分共生圖解和組分分析,1.,礦物組合及其確定標志,在共生分析中，把一定化學成分巖石達到化學平衡時的礦物成分稱為,礦物組合,（,mineral assemblage,）或,礦物共生組合,（,mineral paragenesis,）,(P311),。,確定礦物共生組合的主要標準,（,1,）一個礦物共生組合中各種礦物相互接觸；,（,2,）一個礦物共生組合的各礦物，相互間無反應和交代現(xiàn)象；,（,3,）一個礦物共生組合中，同種礦物的化學成分及光性特征應相近。如有環(huán)帶，則其邊部化學成分及光性特征近似；,（,4,）一個礦物共生組合中的一對礦物之間元素的分配符合,Nernst,分配定律，即各處元素的分配系數(shù)近相等；,（,5,）礦物共生組合中礦物共生關系應符合礦物相律，即礦物相數(shù)不超過惰性組分數(shù)。,共生與共存,共生與共存是兩個完全不同的概念。,共存：,具有不同物理特征和,/,或化學特征的,相，,同時間、空間呈集合體存在，相之間的關系不一定服從熱力學定律。,共生：,同時空呈集合體存在的,相，,在相同物理化學條件下形成，并達到熱力學平衡。體系的內能最低。,變質相與變質相系列,變質相：,Eskola,（,1920,）,：一個變質相是指類似的溫度、壓力條件下達到化學平衡的所有巖石總和,(,不論其結晶方式），一個變質相內部，隨著巖石總體化學成分的改變，其礦物組合作有規(guī)律的改變。,Fyfe and Turner,（,1966,）,：一個變質相是指一定的溫度、壓力區(qū)間內的一整套變質礦物共生組合，它們在時間上、空間上反復出現(xiàn)并緊密地伴生在一起，一個變質相內部其礦物組合與巖石總體化學成分之間有著固定的、因而也是可以預測的對應關系。,Turner 1981,年提出變質相的分類,接觸變質相：,（以溫度增高為序）鈉長綠簾角巖相，普通角閃石角巖相 ，輝石角巖相，透長石相。,區(qū)域變質相,:,沸石相，葡萄石,綠纖石相 ，綠片巖相，藍閃石,硬柱石相，綠簾角閃巖相，角閃巖相，麻粒巖相，榴輝巖相,接觸變質巖相,1.,鈉長綠簾角巖相（,AEH,）：,低溫,溫度約為,300-400,。,C,，壓力,0.1-0.4GPa,特征礦物組合：鈉長石,+,綠簾石,+,透閃石或陽起石,。沒有鈣質斜長石和鋁質角閃石。鐵質堇青石和黑云母出現(xiàn)于低溫部分，紅柱石出現(xiàn)溫度稍高，有時又葉蠟石。特征巖石是斑點板巖。,2.,普通角閃石角巖相（,HH,）：,中溫,溫度約,400-650,。,C,，壓力為,0.1-0.3GPa,特征礦物組合：斜長石,+,普通角閃石,可以有透輝石，而沒有斜方輝石。變質泥質巖與長英質巖石中紅柱石，堇青石不與鉀長石共生。,3.,輝石角巖相（,PH,）,:,高溫,溫度約,650-800,。,C,，壓力不超過,0.2GPa,夕線石，正長石，,紫蘇輝石,或硅灰石為標志礦物,白云母,+,石英不穩(wěn)定。紅柱石，堇青石，夕線石開始與正長石穩(wěn)定共存。特征礦物組合,:,斜長石,+,透輝石,+,紫蘇輝石,4.,透長石相（,S,）,:,極高溫溫度約,800-1100,。,C,，壓力極低，,0.02-0.08GPa,黃長石，鈣鎂橄欖石，斜硅鈣石和透長石等為特征礦物,特征礦物組合,:,斜長石,+,普通輝石,+,易變輝石,。,Facies of low pressure,Albite-epidote hornfels, hornblende hornfels, and pyroxene hornfels facies: contact metamorphic terranes and regional terranes with very high geothermal gradient.,Metamorphic Facies,Sanidinite facies is rare- limited to xenoliths in basic magmas and the innermost portions of some contact aureoles adjacent to hot basic intrusives,區(qū)域變質巖相,沸石相,(Z,或,ZE),：很低溫溫度約,200-300,。,C,，壓力為,。特征礦物組合：鈉長石,+,濁沸石,+,綠泥石,+,葡萄石,石英。,葡萄石,-,綠纖石相（,PP,）：很低溫溫度約,360-400,。,C,，壓力為,。特征礦物組合：,鈉長石,+,葡萄石,+,綠纖石,+,綠泥石,多硅白云母,石英。,藍閃石,-,硬柱石片巖相（,GL,）：很低溫溫度,200-450,。,C,，壓力,0.3-0.8GPa.,特征礦物組合：（低壓）硬柱石,+,鈉長石,+,綠泥石；（高壓）藍閃石,+,硬柱石,+,硬玉質輝石,+,石英。是一個范圍很寬的低溫高壓變質相，有時含有文石，完全不含黑云母。壓力有時可達到,1GPa,或更高。,4.,綠片巖相,(GS,）,:,低溫,溫度約,400-500,。,C,，壓力。特征礦物組合：（泥質巖石）鈉長石,+,綠簾石,+,白云母,+,綠泥石,+,石英 （基性巖石）鈉長石,+,綠簾石,+,綠泥石,+,陽起石；,高溫部分出現(xiàn)黑云母，高壓部分出現(xiàn)黑硬綠泥石，硬綠泥石和鐵鋁榴石。葉蠟石和硬綠泥石等不與鉀長石共生。,5.,綠簾角閃巖相,(EA):,低溫,特征礦物組合：鈉長石,+,綠簾石,+,普通角閃石（,+,鐵鋁榴石）,.,低壓條件下，鈣質斜長石的形成溫度低于普通角閃石時，便不能生成綠簾角閃巖相的共生。而形成斜長陽起石相。,6.,角閃巖相,(A,或,AM):,中溫溫度約,500-700,。,C,，壓力,0.3-0.8GPa,普通角閃石和斜長石的共生是本相的標志,可以有透輝石沒有斜方輝石。泥質巖中除了石英，白云母和黑云母外，低壓相系含紅柱石，堇青石和夕線石，中壓相系含十字石，藍晶石和鐵鋁榴石。高溫部分夕線石，鐵鋁榴石開始與正長石穩(wěn)定共生。,7.,麻粒巖相,(G):,高溫溫度,700-900,。,C,，壓力,0.3-1.2GPa,出現(xiàn)斜方輝石為標志巖石主要由無水礦物所組成，少量黑云母和普通角閃石一般是富,Ti,的變種。,8.,榴輝巖相,(E):,高壓溫度,300-900,。,C,，壓力大于,1GPa,特征礦物組合：綠輝石,+,石榴子石不含長石。一般呈不大的塊體在其它巖石中作為包體。溫度范圍很寬，壓力極大。,變質相系,接觸變質相系,:,dT/dP>=80,硅灰石，堇青石，紅柱石，（基本不含硅線石，不含十字石）,低壓區(qū)域變質相系, dT/dP=80-40,紅柱石，硅線石，堇青石，（不含硅灰石，藍晶石，基本不含十字石）,中壓區(qū)域變質相系, dT/dP=20-40,濁沸石，藍晶石，硅線石，十字石（不含紅柱石，堇青石，藍閃石，硬玉）,高壓區(qū)域變質相系, dT/dP=20-5,硬柱石，藍晶石，藍閃石，硬玉（不含硅線石，濁沸石）,Fig. Temperature-pressure diagram showing the three major types of metamorphic facies series proposed by Miyashiro (1973, 1994).,Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.,變質相與變質相系列,變質相系列：,同一地區(qū)通常不止一個變質相，可以由許多不同的變質相組成，構成變質相的系列；并且不同地區(qū)甚至同一地區(qū)不同地段變質相系列不一樣。最著名的是本世紀,50,年代末期，日本地質學家都城秋穗在研究日本,",三波川帶,",和,",領家?guī)?",時，發(fā)現(xiàn)同一地區(qū)可以存在兩個不同的變質相組合。他指出，,在變質帶中，從低溫向高溫的的變化可以定義為一個相系列，或者稱作變質相系,。并且他認為,每一種特定的變質相系列都反映了各自的特定地熱梯度類型和所經(jīng)歷的事件和演化進程,，這就是變質相系列的實質。,變質相與變質相系列,(1),大體上的等物理系，標志是一系列特征的礦物共生組合,(2),變質相是由變質反應來標定界線,(3),時間上、空間上反復出現(xiàn)是指同一變質相的巖石在不同時間，不同地區(qū)經(jīng)常重復出現(xiàn)，并伴隨在一起。,2) Facies of medium pressure,Most metamorphic rocks now exposed belong to the,greenschist,amphibolite, or,granulite,facies,The,greenschist,and,amphibolite,facies conform to the “typical” geothermal gradient,Metamorphic Facies,Metamorphic Facies,Zeolite,and,prehnite-pumpellyite,facies are thus not always represented, and the,greenschist,facies is the lowest grade developed in many regional terranes,4) Facies of low grades,Rocks often fail to recrystallize thoroughly at very low grades, and equilibrium is not always attained,Metamorphic P-T-t paths may be addressed by:,1) Observing partial overprints of one mineral assemblage upon another,The relict minerals may indicate a portion of either the prograde or retrograde path (or both) depending upon when they were created,Pressure-Temperature-Time (P-T-t) Paths,Metamorphic P-T-t paths may be addressed by:,2) Apply geothermometers and geobarometers to the core vs. rim compositions of chemically zoned minerals to document the changing P-T conditions experienced by a rock during their growth,Pressure-Temperature-Time (P-T-t) Paths,Chemical zoning profiles across a garnet from the Tauern Window. After Spear (1989),Fig.,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,. Mineral. Soc. Amer. Monograph 1.,Metamorphic P-T-t paths may be addressed by:,Even under the best of circumstances (1) overprints and (2) geothermobarometry can usually document only a small portion of the full P-T-t path,3) We thus rely on “forward” heat-flow models for various tectonic regimes to compute more complete P-T-t paths, and evaluate them by comparison with the results of the backward methods,Pressure-Temperature-Time (P-T-t) Paths,Classic view: regional metamorphism is a result of deep burial or intrusion of hot magmas,Plate tectonics: regional metamorphism is a result of crustal thickening and heat input during orogeny at convergent plate boundaries (not simple burial),Heat-flow models have been developed for various regimes, including burial, progressive thrust stacking, crustal doubling by continental collision, and the effects of crustal anatexis and magma migration,Higher than the normal heat flow is required for typical greenschist-amphibolite medium P/T facies series,Uplift and erosion has a fundamental effect on the geotherm and must be considered in any complete model of metamorphism,Pressure-Temperature-Time (P-T-t) Paths,Fig.,Schematic pressure-temperature-time paths based on heat-flow models. The Al,2,SiO,5,phase diagram and two hypothetical dehydration curves are included. Facies boundaries, and facies series from Figs. 25-2 and 25-3.,Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.,Broad agreement between the forward (model) and backward (geothermobarometry) techniques regarding P-T-t paths,The general form of a path such as (a) therefore probably represents a typical rock during orogeny and regional metamorphism,Pressure-Temperature-Time (P-T-t) Paths,1. Contrary to the classical treatment of metamorphism, temperature and pressure do not both increase in unison as a single unified “metamorphic grade.”,Their relative magnitudes vary considerably during the process of metamorphism,Pressure-Temperature-Time (P-T-t) Paths,2. P,max,and T,max,do not occur at the same time,In the usual “clockwise” P-T-t paths, P,max,occurs much earlier than T,max,.,T,max,should represent the maximum grade at which chemical equilibrium is “frozen in” and the metamorphic mineral assemblage is developed,This occurs at a pressure well below P,max, which is uncertain because a mineral geobarometer should record the pressure of T,max,“Metamorphic grade” should refer to the temperature and pressure at T,max, because the grade is determined via reference to the equilibrium mineral assemblage,Pressure-Temperature-Time (P-T-t) Paths,3. Some variations on the cooling-uplift portion of the “clockwise” path (a) indicate some surprising circumstances,For example, the kyanite,sillimanite transition is generally considered a prograde transition (as in path a,1,), but path a,2,crosses the kyanite,sillimanite transition as temperature is,decreasing.,This may result in only minor replacement of kyanite by sillimanite during such a retrograde process,Pressure-Temperature-Time (P-T-t) Paths,Fig. 25-12a.,Schematic pressure-temperature-time paths based on a,crustal thickening,heat-flow model. The Al,2,SiO,5,phase diagram and two hypothetical dehydration curves are included. Facies boundaries, and facies series from Figs. 25-2 and 25-3.,Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.,Fig. 25-14.,A typical Barrovian-type metamorphic field gradient and a series of metamorphic P-T-t paths for rocks found along that gradient in the field.,Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.,一、變質巖原巖恢復,1.,變質巖原巖恢復的一般原則,a.,變余特征優(yōu)先原則,b.,巖套類比的原則,c.,等化學的原則,d.,惰性組分的原則,e.,相關性和趨勢性原則,變余結構、構造（沉積巖）,變余斑狀結構（,a,）和變余砂狀結構（,b,）,a.,綠泥片巖，原巖中輝石斑晶為綠泥石交代呈假象；,b.,變質含礫石石英雜砂巖，碎屑為石英和石英巖，膠結物已變?yōu)榧毿〉慕佋颇?、黑云母和石英?變質石英砂巖，遼寧。磨圓的石英顆粒之間分布的石英粘土已經(jīng)變質為絹云母。,變余結構、構造（火成巖）,變余斑狀結構（,a,）和變余砂狀結構（,b,）,a.,綠泥片巖，原巖中輝石斑晶為綠泥石交代呈假象；,b.,變質含礫石石英雜砂巖，碎屑為石英和石英巖，膠結物已變?yōu)榧毿〉慕佋颇浮⒑谠颇负褪ⅰ?B.,巖石化學、地球化學和副礦物,1.,巖石化學,a. K2O>Na2O,b.,圖解法,2.,地球化學,3.,副礦物,a.,碎屑副礦物的有無和含量,b.,副礦物晶形及顏色,