Stable Mineral Assemblages in Metamorphic Rocks Metamorphic Minearl Assemblage 평형을이루는광물조합 평형상태에서, 광물학 ( 그리고각광물들의화학성분 ) 은 T, P, X 에의해결정됨. 광물의성인 은평형상태의광물조합과관련됨. 잔류광물이나후기에변질광물들은특정한상태를 제외하고는고려사항에서배재된다. The Phase Rule in Metamorphic Systems 상률, 평형상태에서시스템에적용됨. F = C P + 2 the phase rule (6-1) P is the number of phases in the system C is the number of components: the minimum number of chemical constituents required to specify every phase in the system F is the number of degrees of freedom: the number of independently variable intensive parameters of state (such as temperature, pressure, the composition of each phase, etc.) 변성지역의전형적인시료 변성대내에서가능성있는시료를선택, 등변성도선상의정확한것은아님. 대신에상다이어그램상에아무곳을취함. divarianti field 내일가능성이있는지점이지만 univariant curve 또는 invariant point 은아님. 가장일반적인상태는 divariant (F = 2) 이며, 압력과온도가광물조합의영향없이독립적으로변할수있다는것을의미한다. 만일 F 2인것이가장일반적인상태라면, 상률은다음과같이그에따라서다음과같이조절될수도있다. F = C P + 2 2 P C (24-1) 이것이 Goldschmidt s mineralogical phase rule 또는단순한 mineralogical phase rule 이다. P = C 암석을위해우리가결정한 C를추정하면아래세가지시나리오를고려할수있다. a) P = C 변성암에서표준 divariant 상태 ( 일반적으로많이만나는상태임 ) 이암석은아마도변성대내의평형광물조합을묘사할것이다. 1
b) P < C 고용체를나타내는일반적인광물시스템 주로화성암에서볼수있는시스템 P = 1 C = 2 Liquid Liquid Plagioclase plus Plagioclase c) P > C 상대적으로재미있는상태이며, 다음셋중한개의상태가적용됨 : 1) F < 2 대상시료가 univariant reaction curve (isogard) 또는 invariant point 지점에서채취되었을경우 (P = 2 or P = 3) 아래세가지시나리오를고려해봐라. C = 1 P = 1 일반적임 P = 2 귀함 P = 3 오로지 invariant point 에해당하는특정한 P-T상태 (3.7 kbar and 500 o C) 2) 변성암내의광물조합이평형상태를이루지못했을경우. 상률 (phase rule) 이란것은평형상태의계 (equilibrium systems) 에서만적용되는것이고, 만일평형상태가되지못했다면, 공존하는 광물들의수는다양해질것임. Figure 21-9. The P-T phase diagram for the system Al 2 SiO 5 calculated using the program TWQ (Berman, 1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 3) 관찰자가정확하게성분 (Components) 의수를선택하지못했을경우. C 의적절한선택을위한가이드라인은 CaAl 2 Si 2 O 8 (anorthite) 같은 1-component system에서시작하면, 우리가여기에추가할수있는주 / 미량성분들의일반 적인세가지타입이존재한다. a) 새로운상을만들어내는성분 CaMgSi 2 O 6 (diopside) 와같은성분을추가하면, 추가정인상들이결과적으로만들어지는데, 예를들어 binary Di-An system에서투휘석 (diopside) 은고상선아래에서 anorthite와공존한다. 3) 관찰자가정확하게성분 (Components) 의수를선택하지못했을경우. b) 다른성분들을치환하는성분을고려해야함. 1-C anorthite system에 NaAlSi 3 O 8 (albite) 같은성분의추가는고상선아래에서 single solid-solution mineral ( 하나의고용체광물 ; plagioclase) 을만드는회장석조 직을형성할것임. Fe 와 Mn 은일반적으로 Mg 를치환 Al 은 Si 를치환하는경우도있음. Na 는 K 를치환하는경우도있음. 2
3) 관찰자가정확하게성분 (Components) 의수를선택하지못했을경우. c) 완벽하게이동 ( 이동성이좋은 ) 하는성분을고려해야함. 자유롭게이동하는유체성분이나유체에잘녹고이동성이좋은성분들 그와같은성분들의화학적활동도 (activity) 가일반적으로그지역암석시스템의외부적요소에의해조절되는경우. 그런것들은변성계를위해유추되는 C에서일반적으로무시됨. 가장단순한변성시스템인 MgO-H 2 O 를고려하면, 이시스템에서가능성있는자연의상 (phases) 은 periclase (MgO), aqueous fluid (H 2 O), 및 brucite (Mg(OH) 2 ) 우리는물이완벽하게이동성이좋은지그렇지않은지에대해서어떻게 H 2 O를다루어야할까? 반응식 (reaction) 은이시스템에서잠재적인상들사이에서 다음과같이발생한다 : MgO + H 2 O Mg(OH) 2 Per + Fluid = Bru 후퇴변성 (retrograde) 반응 ( 암석의냉각및수화작용에서발생 ) 반응커브의냉각작용, 즉, Brucite를형성하는물과 periclase 의반응 : MgO + H 2 O Mg(OH) 2 The System MgO-H 2 O Reaction: periclase가 brucite와공존 : The System MgO-H 2 O P = C + 1 F = 1 (#2 reason to violate the mineral-ogical phase rule) 곡선을벗어난영역에서, 모든 periclase는반응에의해소모되어야만하고 brucite만남아있는상이다. 따라서 P = 1 및 C = 1 이됨. Figure 24-1. P-T phase diagram illustrating the reaction brucite = periclase + water, calculated using the program TWQ of Berman (1988, 1990, 1991). From Winter (2001). An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Periclase + H 2 O react to form brucite MgO + H 2 O Mg(OH) 2 The System MgO-H 2 O MgO + H 2 O Mg(OH) 2 위의반응은물이부족하면, 과잉 periclase가 brucite 안정영 The System MgO-H 2 O 역에서도남아있게됨. 3
만일물이 brucite가완전하게반응하지않을정도로불충분하게존재한다면 Periclase가다이어그램의어떤영역에도안정하게남아있다고결론내리면됨. 다른지점 (univariant curve 가아닌다른영역 ) 에서우리는 two phases 있을것으로예측해야만한다. P = brucite + periclase ( 반응곡선이하의온도 = 물이제한적인환경 ) 또는 P= periclase + water ( 반응곡선이상의온도 ) 무엇이옳바른지어떻게알수있을까? 변성암은다음과같은것을당신에게알려준다. 상률 (phase rule) 은해석을위한도구이지예측을위한것은아니다. 그리고암석이어떻게거동했는지는말해주지않는다. 만일당신이상대적으로적은상의개수의광물조합을보았다면 (e.g. Per or Bru in the MgO-H 2 Osystem) system), 그것은일부성분이이동성이좋은성분이다. 만일종종어떤지역에서다수의상을갖는광물조합을관찰했다면 (e.g. periclase + brucite), 아마도 Univariant curve 상에영역일확률이높고상률을올바르게적용시키기위해 H 2 O 또는 CO 2 같은다른이동성이큰상들을포함하는성분들을요구할수도있다. 상평형도 상평형도는광물조합의화학성분을그래픽적으로도시한것과관련됨. 단순사례 : 사장석성분과같은선형의 2 성분 (C = 2) = 100 An/(An+Ab) 상평형도 3-C 광물성분은삼각형의상평형도다이어그램에도시됨. x, y, z, xz, xyz, and yz 2 어떤변성암에서 5 개의광물조합을가정해보면 x-xy-x 2 z xy-xyz-x 2 z xy-xyz-y xyz-z-x 2 z y-z-xyz Figure 24-2. Hypothetical threecomponent chemographic compatibility diagram illustrating the positions of various stable minerals. Minerals that coexist compatibly under the range of P-T conditions specific to the diagram are connected by tie-lines. After Best (1982) Igneous and Metamorphic Petrology. W. H. Freeman. 공존선 Tie-line 4
이성분들은 5 개의작은삼각형 (A-E) 으로 chemographic diagram 이구분됨. 일반적으로 3 개의상이한지점에적용됨. 따라서 A: x-xy-x 2 z B: xy-xyz-x 2 z C: xy-xyz-y D: xyz-z-x 2 z E: y-z-xyz P = C 만일현재관찰하고있는암석의전암화학성분이 (B) 라면이암석에서나올수있는광물은? 만일당신이공존선상에떨어지는성분 ( 암석의전암성분 ; f) 를취했다면무슨일이일어나는가? A: x-xy-x 2 z B: xy-xyz-x 2 z C: xy-xyz-yxyz y D: xyz-z-x 2 z E: y-z-xyz P = 2 상평형도확실하게묘사된특정다이어그램은일부변성지역에서 P-T conditions 의특정영역을표현하기도함. P 와 T 가변화하면광물들의안정성과그것들의조합이변함. 서로다른변성정도에서다이어그램은다음과같이변화함. 특정광물들이안정하게됨. 동일한광물들의서로다른배열 ( 서로다른 tielines 서로다른공존상-mineral-과연결됨 ) 일부광물들이 solid solution ( 고용체 ) 를나타내는다이어그램의사례 Figure 24-2. Hypothetical three-component chemographic compatibility diagram illustrating the positions of various stable minerals, many of which exhibit solid solution. After Best (1982) Igneous and Metamorphic Petrology. W. H. Freeman. 5
만일공존선상에 X bulk 가존재 (f) 전암성분도시 X bulk in 3-phase triangles F = 2 (P & T) so X min fixed Figure 24-2. Hypothetical three-component chemographic compatibility diagram illustrating the positions of various stable minerals, many of which exhibit solid solution. After Best (1982) Igneous and Metamorphic Petrology. W. H. Freeman. F = C - P + 2 C = P 변성암에서상평형도 가장일반적인자연상태의암석 : SiO 2, Al 2 O 3, K 2 O, CaO, Na 2 O, FeO, MgO, MnO, H 2 O 으로구성 (C = 9) 2 차원적으로쉽게생각할수있는최대성분의개수 : 3성분 (C=3) 그렇다면올바른성분의선택은???? 가장단순한방법을고려 ( 암석의주성분의랭킹 = Top 5) 1) 간단하게무시되는성분 미량원소 오로지하나의광물에만들어가는원소 이동성이좋은성분 (H 2 O, CO 2 etc) 2) 같이결합하는원소 (Combine components) 고용체에서서로간치환을해주는성분 (Fe + Mg) 3) 암석의타입을제한하는원소 Ex) 석회암 : CaO 4) 일부투영법을이용하는경우도있음 AFM diagram 에서흑운모의투영 The ACF Diagram 염기성암석 에서변성광물조합을묘사한간단한 3-C 삼각다이어그램 변성작용동안출현하고사라지는광물들에만집중함. 따라서변성정도를지시하는지시자로사용됨. Figure 24-4. After Ehlers and Blatt (1982). Petrology. Freeman. And Miyashiro (1994) Metamorphic Petrology. Oxford. A =Al2O3, C=CaO, F=FeO???? NO!!!!! 6
The ACF Diagram The three pseudo-components are all calculated on an atomic basis: A = Al 2 O 3 + Fe 2 O 3 -Na 2 O - K 2 O C = CaO - 3.3 P 2 O 5 F = FeO + MgO + MnO The ACF Diagram A = Al 2 O 3 + Fe 2 O 3 -Na 2 O - K 2 O 왜빼는성분이있을까? 일반적인염기성암석에서 Na, K는전형적으로정장석과조장석 (Albite) 를만들기위해 Al과결합함. ACF diagram에서, 장석류를제외한다른 K-bearing metamorphic minerals만존재 장석에서 Al 2 O 3 : Na 2 O or K 2 O 비율 (automic ratio) 은 1:1, 따라서 1:1 비율만큼장석을형성한다가정하고빼주는것임. An example: The ACF Diagram Figure 24-4. After Ehlers and Blatt (1982). Petrology. Freeman. And Miyashiro (1994) Metamorphic Petrology. Oxford. 회장석 (Anorthite) : CaAl 2 Si 2 O 8 A = 1 + 0-0 - 0 = 1, C = 1-0 = 1, and F = 0 Provisional i values sum to 2, so we can normalize to 1.0 by multiplying each value by ½, resulting in A =0.5 C =0.5 F =0 A = Al 2 O 3 + Fe 2 O 3 -Na 2 O - K 2 O C = CaO - 3.3 P 2 O 5 F = FeO + MgO + MnO 특정 P와 T 영역에관련된전형적인 ACF diagram (the kyanite zone in the Scottish Highlands) The AKF Diagram 이질퇴적암 (Pelitic sedimentary rocks) 이 Al 2 O 3 와 K 2 O 를많이 함유하고상대적으로 CaO 를적게갖기때문에 Eskola 가제안한 새로운다이어그램. K 2 O 를갖는광물조합이포함됨. AKF diagram 에서, 세가지성분 : A = Al 2 O 3 + Fe 2 O 3 -Na 2 O - K 2 O - CaO Figure 24-5. After Turner (1981). Metamorphic Petrology. McGraw Hill. K = K 2 O F = FeO + MgO + MnO 7
AKF compatibility diagram (Eskola, 1915) illustrating paragenesis Figure 24-6. After Ehlers and Blatt (1982). Petrology. Freeman. of pelitic hornfelses, Orijärvi region Finland Figure 24-7. After Eskola (1915) and Turner (1981) Metamorphic Petrology. McGraw Hill. 변성니질암에서가장일반적인광물 3종 : andalusite, muscovite, and microcline. 이광물들은 AKF 다이어그램에서별개의지점으로존재 투영법고찰 : 상평형도에서투영 And & Ms 는 ACF diagram에서같은지점에도시되고그리고미사장석은도시되지않음. 따라서 K와 Al 성분이많은이질암류는 ACF diagram을적용하는것이부적절함 Figure 24-7. After Ehlers and Blatt (1982). Petrology. Freeman. 왜 ACF / AKF diagram에서 SiO 2 는배제할까? A 와 C 에서빼낸성분은무엇인가? - Na 2 O - K 2 O CaO, -P 2 O 5 AFM 다이어그램과투영된변성상다이어그램의결점을잘이해하는데도움을줌. 상평형도에서투영 Example- the ternary system: CaO-MgO-SiO 2 ( CMS ) 단순하게 C = CaO, M = MgO, S = SiO 2 이고, 특정 상평형도에서투영 Fo -Mg 2 SiO 4 Per - MgO En - MgSiO 3 Qtz - SiO 2 Di -CaMgSi 2 O 6 Cc - CaCO 3 원소나상에대한제거작업을하지않는방법을생각해보자. 아래의광물을 CMS 다이어그램에도시해보면 : Fo - Mg 2 SiO 4 Per - MgO En - MgSiO 3 Qtz - SiO 2 Di - CaMgSi 2 O 6 Cc - CaCO 3 8
The line intersects the M-S the side at a point equivalent to 33% MgO 67% SiO 2 Note that any point on the dashed line from C through Di to the M-S side has a constant ratio of Mg:Si = 1:2 상평형도에서투영 Fo -Mg 2 SiO 4 Per - MgO En - MgSiO 3 Qtz - SiO 2 Di -CaMgSi 2 O 6 Cc - CaCO 3 Pseudo-binary Mg-Si diagram in which Di is projected to a 33 Mg - 66 Si (1:2) + Cal Di - CaMgSi 2 O 6 MgO Per Fo En Di' SiO 2 Q Could project Di from SiO 2 and get C= 0.5, M =0.5 (1:1) 상평형도에서투영 상평형도에서투영 MgO SiO 2 Per Fo En Di' Q Di - Ca 1 Mg 1 Si 2 O 6 + Qtz MgO Per, Fo, En Di' CaO Cal 광물학적인상률 (P = C) 과연관지으면아래의 2-phase 광물조합이위의 2- component system에서적용됨. Per + Fo Fo + En En + Di Di + Q 상평형도에서투영 ACF and AKF diagrams에서 SiO 2 배제 : 석영으로부터투영 가장간단한이유 : 어떤정점으로부터투영되는성분은성분에서배제한다. ( 아래그림 C 배제됨 ) 이방식의결점은이러한투영이어떠한크기 ( 차원 ; dimension) 을없애면서까지진정한상관관계를묘사한다는점이다. + Cal MgO SiO 2 Per Fo En Di' Q 투영법 (4 성분계 ) Two compounds plot within the ABCQ compositional tetrahedron, x (formula ABCQ) y (formula A 2 B 2 CQ) Figure 24-12. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 9
투영법 (4 성분계 ) 투영법 (4 성분계 ) x = ABCQ y = A 2 B 2 CQ x = ABCQ y = A 2 B 2 CQ Figure 24-12. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 24-12. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 투영법 (4 성분계 ) x plots as x' since A:B:C = 1:1:1 = 33:33:33 y plots as y' since A:B:C = 2:2:1 = 40:40:20 x = ABCQ y = A 2 B 2 CQ Figure 24-13. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 만일옆의다이어그램이 (q) 로부터투영해서그렸다는것을기억한다면, 아래의광물조합도충분히가능하다는것을알수있다. (q)-a-x-y (q)-b-x-y (q)-a-b-y (q)-a-x-c 오히려 q를제외한광물조합 a-b-c 는불가능한것이되어버림. ( 왜?) 투영법 (4 성분계 ) Fig. 24-13 투영법 (4 성분계 ) Fig. 24-13 A(K)FM Diagram 변성니질암류를위한 AKF 다이어그램의확장버전 비록 AKF 다이어그램이이질암류를표현하기에충분하긴하지만, Thompson (1957) 은 Fe 와 Mg 가대부분의암석에포함되어있는다양한 Mg 가대부분의암석에포함되어있는다양한염기성광물들 ( 석류석, 흑운모, 근청석, 십자석등 ) 에서똑같은비율로들어가지않는것을관찰함. 10
A(K)FM Diagram A(K)FM Diagram Figure 24-17. Partitioning of Mg/Fe in minerals in ultramafic rocks, Bergell aureole, Italy After Trommsdorff and Evans (1972). A J Sci 272, 423-437. A=Al 2 O 3 K = K 2 O F=FeO M=MgO A(K)FM Diagram Muscovite stable Project from a phase that is present in the mineral assemblages to be studied Kfs stable Figure 24-18. AKFM Projection from Mu. After Thompson (1957). Am. Min. 22, 842-858. (a) A simplified petrogenetic grid and (b) pseudosection constructed using the Gibbs program (Spear, 1989) and the dataset of Holland and Powell (1998) (in Cheong, 2008) At high grades muscovite dehydrates to K-feldspar as the common high-k phase Then the AFM diagram should be projected from K-feldspar When projected from Kfs, biotite projects within the F-M base of the AFM triangle A(K)FM Diagram A(K)FM Diagram A = Al 2 O 3-3K 2 O (if projected from Ms) = Al 2 O 3 -K 2 O (if projected from Kfs) F = FeO M = MgO Figure 24-18. AKFM Projection from Kfs. After Thompson (1957). Am. Min. 22, 842-858. 11
Biotite (from Ms): KMg 2 FeSi 3 AlO 10 (OH) 2 A = 0.5-3 (0.5) = - 1 F = 1 M = 2 To normalize we multiply each by 1.0/(2 + 1-1) = 1.0/2 = 0.5 Thus A = -0.5 F = 0.5 M = 1 A(K)FM Diagram Figure 24-20. AFM Projection from Ms for mineral assemblages developed in metapelitic rocks in the lower sillimanite zone, New Hampshire After Thompson (1957). Am. Min. 22, 842-858. Mg-enrichment typically in the order: cordierite > chlorite > biotite > staurolite > garnet A(K)FM Diagram 적절한상평형도의선택 예를들어, 특정지역에서이질암류를 연구한다고가정한다면, 이이질암류의시스템은 9 종류의기본적인성분을포함한다. (SiO 2, Al 2 O 3, FeO, MgO, MnO, CaO, Na 2 O, K 2 O, and H 2 O) Figure 27-6. AFM projections showing the relative distribution of Fe and Mg in garnet vs. biotite at approximately 500 o C (a) and 800 o C (b). From Spear (1993) Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths. Mineral. Soc. Amer. Monograph 1. MSA. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 어떻게우리는이 9 가지성분중에서의미있고 유용한다이어그램을얻어낼수있을까? 적절한상평형도의선택 MnO는 FeO + MgO와같이생각하거나배제 ( 함량이상대적으로매우낮거나또는 FeO and MgO를따라서고용체로행동 ) 적절한상평형도의선택 Common high-grade grade mineral assemblage: Sil-St-Mu-Bt-Qtz-Plag 이질암류에서 Na 2 O는일반적으로사장석에서만중요하다. Na 를사용하고싶지않으면배제 사용하고싶으면조장석을기준으로투영 H 2 O 는상당히이동성이좋으며배제하는성분임. Figure 24-20. AFM Projection from Ms for mineral assemblages developed in metapelitic rocks in the lower sillimanite zone, New Hampshire After Thompson (1957). Am. Min. 22, 842-858. 12
적절한상평형도의선택 적절한상평형도의선택 Figure 24-21. After Ehlers and Blatt (1982). Petrology. Freeman. Figure 24-21. After Ehlers and Blatt (1982). Petrology. Freeman. 적절한상평형도의선택 무수한상평형도가다양한변성암의종류에서성인적인관계를분석하기위하여제안되어왔음. 대부분이삼성분 ( 삼각다이어그램 ) 임 일부자연상에서존재하는시스템은 3- component system에적절함. 결과적인변성상도 (metamorphic phase diagram) 는광물조합의형식에엄격하게적용됨. 다른다이어그램은투영방식으로단순화됨. Figure 28-3. Greenschist facies AKF diagrams (using the Spear, 1993, formulation) showing the biotite-in isograd reaction as a tie-line flip. In (a), below the isograd, the tie-lines connecting chlorite and K-Feldspar shows that the mineral pair is stable. As grade increases the Chl-Kfs field shrinks to a single tie-line. In (b), above the isograd, biotite + phengite is now stable, and chlorite + K-feldspar are separated by the new biotite-phengite tie-line, so they are no longer stable together. Only the most Alpoor portion of the shaded natural pelite range is affected by this reaction. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-4. A series of AKF diagrams (using the Spear, 1993, formulation) illustrating the migration of the Ms-Bt-Chl and Ms-Kfs-Chl sub-triangles to more Al-rich compositions via continuous reactions in the biotite zone of the greenschist facies above the biotite isograd. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 13
Figure 28-5. AFM projection for the biotite zone, greenschist facies, above the chloritoid isograd. The compositional ranges of common pelites and granitoids are shaded. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-6. AFM projection for the upper biotite zone, greenschist facies. Although garnet is stable, it is limited to unusually Fe-rich compositions, and does not occur in natural pelites (shaded). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-7. AFM projection for the garnet zone, transitional to the amphibolite facies, showing the tie-line flip associated with reaction (28-8) (compare to Figure 28-6) which introduces garnet into the more Fe-rich types of common (shaded) pelites. After Spear (1993) Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths. Mineral. Soc. Amer. Monograph 1. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-9. AFM projection in the lower staurolite zone of the amphibolite facies, showing the change in topology associated with reaction (28-9) in which the lower-grade Cld- Ky tie-line (dashed) is lost and replaced by the St-Chl tie-line. This reaction introduced staurolite to only a small range of Al-rich metapelites. After Spear (1993) Metamorphic Phase Equilibria and Pressure-Temperature- Time Paths. Mineral. Soc. Amer. Monograph 1. Figure 28-10. AFM projection in the staurolite zone of the amphibolite facies, showing the change in topology associated with the terminal reaction (28-11) in which chloritoid is lost (lost tie- lines are dashed), d) yielding to the Grt-St-Chl sub-triangle that surrounds it. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-11. AFM diagram for the staurolite zone, amphibolite facies, showing the tie-line flip associated with reaction (28-12) which introduces staurolite into many low-al common pelites (shaded). After Carmichael (1970) J. Petrol., 11, 147-181. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 14
Figure 28-14. AFM projection for the kyanite zone, amphibolite facies, showing the tie-line flip associated with reaction (28-15) which introduces kyanite into many low-al common pelites (shaded). After Carmichael (1970) J. Petrol., 11, 147-181. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-15. AFM projection above the sillimanite and staurolite-out isograds, sillimanite it zone, upper amphibolite facies. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-16. AFM diagram (projected from K-feldspar) above the cordierite-in isograds, granulite facies. Cordierite forms first by reaction (29-14), and then the dashed Sil-Bt tie-line is lost and the Grt-Crd tie-line forms as a result of reaction (28-17). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-17. AFM diagrams (projected from muscovite) for low P/T metamorphism of pelites. a. Cordierite forms between andalusite and chlorite along the Mg-rich side of the diagram via reaction (28-23) in the albiteepidote hornfels facies. b. The compositional range of chloritoid is reduced and that of cordierite expands as the Chl-Cld-And and And-Chl- Crd sub-triangles migrate toward more Fe-rich compositions. Andalusite may be introduced into Al-rich pelites. c. Cordierite is introduced to many Al-rich pelites via reaction (28-24) in the lowermost hornblende hornfels facies. (d) Chlorite is lost in Ms-bearing pelites as a result of reaction (28-25). Created using the program Gibbs (Spear, 1999) Geol. Materials Res., 1, 1-18. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-18.a.The stability range of staurolite on Figure 28-2 (red). b. AFM projection in the hornblende hornfels facies in the vicinity of 530-560 o C at pressures greater than 0.2 GPa, in which staurolite is stable and may occur in some high-fe-al pelites (shaded). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-19. AFM diagrams (projected from Kfs) in the lowermost pyroxene hornfels facies. a. The compositional range of cordierite is reduced as the Crd-And-Bt sub-triangle migrates toward more Mg-rich compositions. Andalusite may be introduced into Al-rich pelites b. Garnet is introduced to many Al-rich pelites via reaction (28-27). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. 15
Figure 28-20. Veins developed in pelitic hornfelses within a few meters of the contact with diorite. The vein composition contrasts with that of the diorite, and suggests that the veins result from localized partial melting of the hornfelses. Onawa aureole, Maine. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-21. High-temperature petrogenetic grid showing the location of selected melting and dehydration equilibria in the Na 2 O-K 2 O- FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O (NKFMASH) system, with sufficient sodium to stabilize albite. Also shown are some equilibria in the KFASH (orange) and KMASH (blue) systems. The medium and low P/T metamorphic field gradients from Figure 28-2 (broad arrows) are included. The Al 2 SiO 5 triple point is shifted as shown to 550 o C and 0.45 GPa following the arguments of Pattison (1992), allowing for the coexistence of andalusite and liquid. V = H 2 O-rich vapor, when present in fluid-saturated rocks. After Spear et al. (1999). Figure 28-22. Some textures of migmatites. a. Breccia structure in agmatite. b. Net-like structure. c. Raft- like structure. d. Vein structure. e. Stromatic, or layered, structure. f. Dilation structure in a boudinaged layer. g. Schleiren structure. h. Nebulitic structure. From Mehnert (1968) Migmatites and the Origin of Granitic Rocks. Elsevier. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 28-23. Complex migmatite textures including multiple generations of concordant bands and cross-cutting veins. Angmagssalik area, E. Greenland. Outcrop width ca. 10 m. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. More complex migmatite textures. 16