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Metamorphic Textures Textures of Regional Metamorphism F Dynamothermal (crystallization under dynamic conditions) F Orogeny- long-term mountain-building.

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Presentation on theme: "Metamorphic Textures Textures of Regional Metamorphism F Dynamothermal (crystallization under dynamic conditions) F Orogeny- long-term mountain-building."— Presentation transcript:

1 Metamorphic Textures Textures of Regional Metamorphism F Dynamothermal (crystallization under dynamic conditions) F Orogeny- long-term mountain-building s May comprise several Tectonic Events i May have several Deformational Phases F May have an accompanying Metamorphic Cycles with one or more Reaction Events

2 Metamorphic Textures Textures of Regional Metamorphism F Tectonite- a deformed rock with a texture that records the deformation F Fabric- the complete spatial and geometric configuration of textural elements s Foliation- planar textural element s Lineation- linear textural element s Lattice Preferred Orientation (LPO) s Dimensional Preferred Orientation (DPO)

3 Progressive syntectonic metamorphism of a volcanic graywacke, New Zealand. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco.

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7 Fig Types of foliations a. Compositional layering b. Preferred orientation of platy minerals c. Shape of deformed grains d. Grain size variation e. Preferred orientation of platy minerals in a matrix without preferred orientation f. Preferred orientation of lenticular mineral aggregates g. Preferred orientation of fractures h. Combinations of the above Figure Types of fabric elements that may define a foliation. From Turner and Weiss (1963) and Passchier and Trouw (1996).

8 Figure A morphological (non-genetic) classification of foliations. After Powell (1979) Tectonophys., 58, 21-34; Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag; and Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

9 Figure (continued)

10 Figure Continuous schistosity developed by dynamic recrystallization of biotite, muscovite, and quartz. a. Plane-polarized light, width of field 1 mm. b. Crossed-polars, width of field 2 mm. Although there is a definite foliation in both samples, the minerals are entirely strain-free. a b

11 Progressive development (a  c) of a crenulation cleavage for both asymmetric (top) and symmetric (bottom) situations. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

12 Figure 23-24a. Symmetrical crenulation cleavages in amphibole-quartz-rich schist. Note concentration of quartz in hinge areas. From Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag.

13 Figure 23-24b. Asymmetric crenulation cleavages in mica-quartz-rich schist. Note horizontal compositional layering (relict bedding) and preferential dissolution of quartz from one limb of the folds. From Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag.

14 Development of S 2 micas depends upon T and the intensity of the second deformation Figure Stages in the development of crenulation cleavage as a function of temperature and intensity of the second deformation. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

15 Types of lineations a. Preferred orientation of elongated mineral aggregates b. Preferred orientation of elongate minerals c. Lineation defined by platy minerals d. Fold axes (especially of crenulations) e. Intersecting planar elements. Figure Types of fabric elements that define a lineation. From Turner and Weiss (1963) Structural Analysis of Metamorphic Tectonites. McGraw Hill.

16 Figure Proposed mechanisms for the development of foliations. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

17 Figure Development of foliation by simple shear and pure shear (flattening). After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

18 Development of an axial-planar cleavage in folded metasediments. Circular images are microscopic views showing that the axial- planar cleavage is a crenulation cleavage, and is developed preferentially in the micaceous layers. From Gilluly, Waters and Woodford (1959) Principles of Geology, W.H. Freeman; and Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco.

19 Diagram showing that structural and fabric elements are generally consistent in style and orientation at all scales. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco.

20 Pre-kinematic crystals a.Bent crystal with undulose extinction b.Foliation wrapped around a porphyroblast c.Pressure shadow or fringe d.Kink bands or folds e.Microboudinage f.Deformation twins Figure Typical textures of pre- kinematic crystals. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

21 Post-kinematic crystals a.Helicitic folds b. Randomly oriented crystals c. Polygonal arcs d. Chiastolite e. Late, inclusion-free rim on a poikiloblast (?) f. Random aggregate pseudomorph Figure Typical textures of post- kinematic crystals. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

22 Syn-kinematic crystals Paracrystalline microboudinageSpiral Porphyroblast Figure Syn-crystallization micro-boudinage. Syn-kinematic crystal growth can be demonstrated by the color zoning that grows and progressively fills the gap between the separating fragments. After Misch (1969) Amer. J. Sci., 267, Figure Traditional interpretation of spiral S i train in which a porphyroblast is rotated by shear as it grows. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

23 Syn-kinematic crystals Figure Spiral S i train in garnet, Connemara, Ireland. Magnification ~20X. From Yardley et al. (1990) Atlas of Metamorphic Rocks and their Textures. Longmans.

24 Syn-kinematic crystals Figure Non-uniform distribution of shear strain as proposed by Bell et al. (1986) J. Metam. Geol., 4, Blank areas represent high shear strain and colored areas are low-strain. Lines represent initially horizontal inert markers (S 1 ). Note example of porphyroblast growing preferentially in low-strain regions.

25 Syn-kinematic crystals Figure “Snowball garnet” with highly rotated spiral S i. Porphyroblast is ~ 5 mm in diameter. From Yardley et al. (1990) Atlas of Metamorphic Rocks and their Textures. Longmans.

26 Figure S i characteristics of clearly pre-, syn-, and post-kinematic crystals as proposed by Zwart (1962). a. Progressively flattened S i from core to rim. b. Progressively more intense folding of S i from core to rim. c. Spiraled S i due to rotation of the matrix or the porphyroblast during growth. After Zwart (1962) Geol. Rundschau, 52,

27 Analysis of Deformed Rocks l Deformational events: D 1 D 2 D 3 … l Metamorphic events: M 1 M 2 M 3 … l Foliations: S o S 1 S 2 S 3 … l Lineations: L o L 1 L 2 L 3 … l Plot on a metamorphism-deformation-time plot showing the crystallization of each mineral

28 Analysis of Deformed Rocks Figure (left) Asymmetric crenulation cleavage (S 2 ) developed over S 1 cleavage. S 2 is folded, as can be seen in the dark sub-vertical S 2 bands. Field width ~ 2 mm. Right: sequential analysis of the development of the textures. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

29 Analysis of Deformed Rocks Figure Graphical analysis of the relationships between deformation (D), metamorphism (M), mineral growth, and textures in the rock illustrated in Figure Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

30 Figure Composite sketch of some common textures in Pikikiruna Schist, N.Z. Garnet diameter is ~ 1.5 mm. From Shelley (1993) Igneous and Metamorphic Rocks Under the Microscope. Chapman and Hall. Analysis of Deformed Rocks Figure Graphical analysis of the relationships between deformation (D), metamorphism (M), mineral growth, and textures in the rock illustrated in Figure Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

31 Figure Textures in a hypothetical andalusite porphyryoblast-mica schist. After Bard (1986) Microtextures of Igneous and Metamorphic Rocks. Reidel. Dordrecht. Figure Graphical analysis of the relationships between deformation (D), metamorphism (M), mineral growth, and textures in the rock illustrated in Figure Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

32 Figure 23-48a. Interpreted sequential development of a polymetamorphic rock. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

33 Figure 23-48b. Interpreted sequential development of a polymetamorphic rock. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

34 Figure 23-48c. Interpreted sequential development of a polymetamorphic rock. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

35 From Yardley (1989) An Introduction to Metamorphic Petrology. Longman. Post-kinematic: S i is identical to and continuous with S e Pre-kinematic: Porphyroblasts are post-S 2. S i is inherited from an earlier deformation. S e is compressed about the porphyroblast in (c) and a pressure shadow develops. Syn-kinematic: Rotational porphyroblasts in which S i is continuous with S e suggesting that deformation did not outlast porphyroblast growth.

36 Deformation may not be of the same style or even coeval throughout an orogen Stage I: D 1 in forearc (A) migrates away from the arc over time. Area (B) may have some deformation associated with pluton emplacement, area (C) has no deformation at all Figure Hypothetical development of an orogenic belt involving development and eventual accretion of a volcanic island arc terrane. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

37 Deformation may not be of the same style or even coeval throughout an orogen Stage II: D 2 overprints D 1 in forearc (A) in the form of sub-horizontal folding and back-thrusting as pushed against arc crust. Area (C) begins new subduction zone with thrusting and folding migrating toward trench. Figure Hypothetical development of an orogenic belt involving development and eventual accretion of a volcanic island arc terrane. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

38 Deformation may not be of the same style or even coeval throughout an orogen Stage III: Accretion deforms whole package. More resistant arc crust gets a D 1 event. D 2 overprints D 1 in forearc (A) and in pluton-emplacement structures in (B). Area (C) in the suture zone gets D 3 overprinting D 2 recumbent folds on D 1 foliations. Figure Hypothetical development of an orogenic belt involving development and eventual accretion of a volcanic island arc terrane. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

39 Deformation may not be of the same style or even coeval throughout an orogen The orogen as it may now appear following uplift and erosion. Figure Hypothetical development of an orogenic belt involving development and eventual accretion of a volcanic island arc terrane. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

40 Figure Reaction rims and coronas. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

41 Figure Portion of a multiple coronite developed as concentric rims due to reaction at what was initially the contact between an olivine megacryst and surrounding plagioclase in anorthosites of the upper Jotun Nappe, W. Norway. From Griffen (1971) J. Petrol., 12,

42 Photomicrograph of multiple reaction rims between olivine (green, left) and plagioclase (right).

43 Coronites in outcrop. Cores of orthopyroxene (brown) with successive rims of clinopyroxene (dark green) and garnet (red) in an anorthositic matrix. Austrheim, Norway.

44 Figures not used Figure a. Migration of a vacancy in a familiar game. b. Plastic horizontal shortening of a crystal by vacancy migration. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag. Berlin.

45 Figures not used Figure Plastic deformation of a crystal lattice (experiencing dextral shear) by the migration of an edge dislocation (as viewed down the axis of the dislocation).

46 Figures not used Figure Gneissic anorthositic ‑ amphibolite (light color on right) reacts to become eclogite (darker on left) as left-lateral shear transposes the gneissosity and facilitates the amphibolite ‑ to ‑ eclogite reaction. Bergen area, Norway. Two-foot scale courtesy of David Bridgwater. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

47 Figures not used Figure Skeletal or web texture of staurolite in a quartzite. The gray intergranular material, and the mass in the lower left, are all part of a single large staurolite crystal. Pateca, New Mexico. Width of view ~ 5 mm. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

48 Figures not used Figure 23-16a. Large polygonized quartz crystals with undulose extinction and subgrains that show sutured grain boundaries caused by recrystallization. Compare to Figure 23-15b, in which little, if any, recrystallization has occurred. From Urai et al. (1986) Dynamic recrystallization of minerals. In B. E. Hobbs and H. C. Heard (eds.), Mineral and Rock Deformation: Laboratory Studies. Geophysical Monograph 36. AGU.

49 Figures not used Figure 23-16b. Vein-like pseudotachylite developed in gneisses, Hebron Fjord area, N. Labrador, Canada. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

50 Figures not used Figure Some features that permit the determination of sense-of-shear. All examples involve dextral shear.  1 is oriented as shown. a. Passive planar marker unit (shaded) and foliation oblique to shear planes. b. S-C foliations. c. S-C’ foliations. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

51 Figures not used Figure Augen Gneiss. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

52 Figures not used Figure Mantled porphyroclasts and “mica fish” as sense-of-shear indicators. After Passchier and Simpson (1986) Porphyroclast systems as kinematic indicators. J. Struct. Geol., 8,

53 Figures not used Figure Other methods to determine sense-of-shear. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

54 Figures not used Figure Deformed quartzite in which elongated quartz crystals following shear, recovery, and recrystallization. Note the broad and rounded suturing due to coalescence. Field width ~ 1 cm. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

55 Figures not used Figure Kink bands involving cleavage in deformed chlorite. Inclusions are quartz (white), and epidote (lower right). Field of view ~ 1 mm. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

56 Figures not used Figure Examples of petrofabric diagrams. a. Crystal c-axes cluster in a shallow inclination to the NE. b. Crystal axes form a girdle of maxima that represents folding of an earlier LPO. Poles cluster as normals to fold limbs.  represents the fold axis. The dashed line represents the axial plane, and suggests that  1 was approximately E - W and horizontal. From Turner and Weiss (1963) Structural Analysis of Metamorphic Tectonites. McGraw Hill.

57 Figures not used Figure Pelitic schist with three s-surfaces. S 0 is the compositional layering (bedding) evident as the quartz-rich (left) half and mica-rich (right) half. S 1 (subvertical) is a continuous slaty cleavage. S 2 (subhorizontal) is a later crenulation cleavage. Field width ~4 mm. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

58 Figures not used Figure Illustration of an Al 2 SiO 5 poikiloblast that consumes more muscovite than quartz, thus inheriting quartz (and opaque) inclusions. The nature of the quartz inclusions can be related directly to individual bedding substructures. Note that some quartz is consumed by the reaction, and that quartz grains are invariably rounded. From Passchier and Trouw (1996) Microtectonics. Springer- Verlag.

59 Figures not used Figure Initial shear strain causes transposition of foliation. c. Continued strain during the same phase causes folding of the foliation. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

60 Figures not used Figure a. Mesh texture in which serpentine (dark) replaces a single olivine crystal (light) along irregular cracks. b. Serpentine pseudomorphs orthopyroxene to form bastite in the upper portion of photograph, giving way to mesh olivine below. Field of view ca. 0.1 mm. Fidalgo sepentinite, WA state. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. ab


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