Metamorphic Textures Textures of Regional Metamorphism F Dynamothermal (crystallization under...

Metamorphic TexturesMetamorphic TexturesTextures of Regional MetamorphismTextures of Regional Metamorphism

DynamothermalDynamothermal (crystallization under dynamic (crystallization under dynamic conditions)conditions)

OrogenyOrogeny- long-term mountain-building- long-term mountain-building May comprise several May comprise several Tectonic EventsTectonic Events

May have several May have several Deformational PhasesDeformational Phases May have an accompanying May have an accompanying Metamorphic CyclesMetamorphic Cycles

with one or more with one or more Reaction EventsReaction Events

Metamorphic TexturesMetamorphic TexturesTextures of Regional MetamorphismTextures of Regional Metamorphism

Tectonite- Tectonite- a deformed rock with a texture that a deformed rock with a texture that records the deformationrecords the deformation

Fabric-Fabric- the complete spatial and geometric the complete spatial and geometric configuration of textural elementsconfiguration of textural elements

Foliation-Foliation- planar textural element planar textural element Lineation-Lineation- linear textural element linear textural element Lattice Preferred Orientation (LPO)Lattice Preferred Orientation (LPO) Dimensional Preferred Orientation (DPO)Dimensional Preferred Orientation (DPO)

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

Fig 23-21 Types of foliationsFig 23-21 Types of foliationsa.a. Compositional layering Compositional layeringb.b. Preferred orientation of platy Preferred orientation of platy

mineralsmineralsc.c. Shape of deformed grains Shape of deformed grainsd.d. Grain size variation Grain size variatione.e. Preferred orientation of platy Preferred orientation of platy

minerals in a matrix without minerals in a matrix without preferred orientationpreferred orientation

f.f. Preferred orientation of Preferred orientation of lenticular mineral aggregateslenticular mineral aggregates

g.g. Preferred orientation of Preferred orientation of fracturesfractures

h.h. Combinations of the above Combinations of the above Figure 23-21. Types of fabric elements that may define a foliation. From Turner and Weiss (1963) and Passchier and Trouw (1996).

Figure 23-22. 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.

Figure 23-22. (continued)

Figure 23-23. 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

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

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.

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.

Development of SDevelopment of S22 micas depends upon T micas depends upon T

and the intensity of the second deformationand the intensity of the second deformation

Figure 23-25. 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.

Types of lineationsTypes of lineationsa.a. Preferred orientation Preferred orientation

of elongated of elongated mineral aggregatesmineral aggregates

b.b. Preferred Preferred orientation of orientation of elongate mineralselongate minerals

c.c. Lineation defined by Lineation defined by platy mineralsplaty minerals

d.d. Fold axes Fold axes (especially of (especially of crenulations)crenulations)

e.e. Intersecting planar Intersecting planar elements.elements.

Figure 23-26. Types of fabric elements that define a lineation. From Turner and Weiss (1963) Structural Analysis of Metamorphic Tectonites. McGraw Hill.

Figure 23-27. Proposed mechanisms for the development of foliations. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

Figure 23-28. Development of foliation by simple shear and pure shear (flattening). After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

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.

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.

Pre-kinematic Pre-kinematic crystalscrystals

a.a. Bent crystal with Bent crystal with undulose undulose extinctionextinction

b.b. Foliation Foliation wrapped around wrapped around a porphyroblasta porphyroblast

c.c. Pressure shadow Pressure shadow or fringeor fringe

d.d. Kink bands or Kink bands or foldsfolds

e.e. MicroboudinageMicroboudinagef.f. Deformation Deformation

twinstwins

Figure 23-34. Typical textures of pre-kinematic crystals. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

Post-kinematic crystalsPost-kinematic crystalsa.a. Helicitic folds Helicitic folds b.b. Randomly oriented crystals Randomly oriented crystals c.c. Polygonal arcs Polygonal arcs

d.d. Chiastolite Chiastolite e.e. Late, inclusion-free rim on a poikiloblast (?) Late, inclusion-free rim on a poikiloblast (?) f.f. Random aggregate pseudomorph Random aggregate pseudomorph

Figure 23-35. Typical textures of post-kinematic crystals. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.

Syn-kinematic crystalsSyn-kinematic crystals

Paracrystalline microboudinageParacrystalline microboudinage Spiral PorphyroblastSpiral Porphyroblast

Figure 23-36. 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, 43-63.

Figure 23-38. Traditional interpretation of spiral Si train in which a porphyroblast is

rotated by shear as it grows. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.


Figure 23-38. Spiral Si

train in garnet, Connemara, Ireland. Magnification ~20X. From Yardley et al. (1990) Atlas of Metamorphic Rocks and their Textures. Longmans.


Figure 23-40. Non-uniform distribution of shear strain as proposed by Bell et al. (1986) J. Metam. Geol., 4, 37-67. Blank areas represent high shear strain and colored areas are low-strain. Lines represent initially horizontal inert markers (S1). Note example of porphyroblast growing

preferentially in low-strain regions.


Figure 23-38. “Snowball garnet” with highly rotated spiral Si.

Porphyroblast is ~ 5 mm in diameter. From Yardley et al. (1990) Atlas of Metamorphic Rocks and their Textures. Longmans.

Figure 23-37. Si characteristics of clearly pre-, syn-, and post-kinematic crystals as proposed by Zwart (1962). a. Progressively

flattened Si from core to rim. b. Progressively more intense folding of S i from core to rim. c. Spiraled Si due to rotation of the matrix

or the porphyroblast during growth. After Zwart (1962) Geol. Rundschau, 52, 38-65.

Analysis of Deformed RocksAnalysis of Deformed Rocks

Deformational events: DDeformational events: D11 D D22 D D33 … …

Metamorphic events: MMetamorphic events: M11 M M22 M M33 … …

Foliations: SFoliations: Soo S S11 S S22 S S33 … …

Lineations: LLineations: Loo L L11 L L22 L L33 … … Plot on a metamorphism-deformation-time plot Plot on a metamorphism-deformation-time plot

showing the crystallization of each mineralshowing the crystallization of each mineral


Figure 23-42. (left) Asymmetric crenulation cleavage (S2)

developed over S1

cleavage. S2 is

folded, as can be seen in the dark sub-vertical S2

bands. Field width ~ 2 mm. Right: sequential analysis of the development of the textures. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag.


Figure 23-43. Graphical analysis of the relationships between deformation (D), metamorphism (M), mineral growth, and textures in the rock illustrated in Figure 23-42. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Figure 23-44. 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.



Figure 23-46. Textures in a hypothetical andalusite porphyryoblast-mica schist. After Bard (1986) Microtextures of Igneous and Metamorphic Rocks. Reidel. Dordrecht.


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

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

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

From Yardley (1989) An Introduction to Metamorphic Petrology. Longman.

Post-kinematic: Si is identical to and continuous with Se

Pre-kinematic: Porphyroblasts are post-S2. Si is inherited from an earlier deformation. Se is compressed about the porphyroblast in (c) and a pressure shadow develops.

Syn-kinematic: Rotational porphyroblasts in which Si is continuous with Se suggesting that deformation did not outlast porphyroblast growth.

Deformation may not be of the same style or Deformation may not be of the same style or even coeval throughout an orogeneven coeval throughout an orogen

Stage I:Stage I: D D11 in forearc (A) migrates away from the arc in forearc (A) migrates away from the arc

over time. Area (B) may have some deformation over time. Area (B) may have some deformation associated with pluton emplacement, area (C) has no associated with pluton emplacement, area (C) has no deformation at alldeformation at all

Figure 23-49. 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.


Stage II:Stage II: D D22 overprints D overprints D11 in forearc (A) in the form of in forearc (A) in the form of

sub-horizontal folding and back-thrusting as pushed sub-horizontal folding and back-thrusting as pushed against arc crust. Area (C) begins new subduction zone against arc crust. Area (C) begins new subduction zone with thrusting and folding migrating toward trench.with thrusting and folding migrating toward trench.



Stage III:Stage III: Accretion deforms whole package. More Accretion deforms whole package. More resistant arc crust gets a Dresistant arc crust gets a D11 event. D event. D22 overprints D overprints D11 in in

forearc (A) and in pluton-emplacement structures in (B). forearc (A) and in pluton-emplacement structures in (B). Area (C) in the suture zone gets DArea (C) in the suture zone gets D33 overprinting D overprinting D22

recumbent folds on Drecumbent folds on D11 foliations. foliations.Figure 23-49. 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.


The orogen as it may now appear following uplift and The orogen as it may now appear following uplift and erosion.erosion.


Figure 23-53. Reaction rims and coronas. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag.

Figure 23-54. 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, 219-243.

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

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

Figures not usedFigures not used

Figure 23-2. 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.


Figure 23-3. Plastic deformation of a crystal lattice (experiencing dextral shear) by the migration of an edge dislocation (as viewed down the axis of the dislocation).


Figure 23-8. 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.


Figure 23-12. 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.


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.


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.


Figure 23-17. 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.


Figure 23-18. Augen Gneiss. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 23-19. Mantled porphyroclasts and “mica fish” as sense-of-shear indicators. After Passchier and Simpson (1986) Porphyroclast systems as kinematic indicators. J. Struct. Geol., 8, 831-843.


Figure 23-20. Other methods to determine sense-of-shear. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 23-29. 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.


Figure 23-30. 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.


Figure 23-31. 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.


Figure 23-32. Pelitic schist with three s-surfaces. S0 is the compositional layering (bedding) evident as the quartz-rich (left) half and

mica-rich (right) half. S1 (subvertical) is a continuous slaty cleavage. S2 (subhorizontal) is a later crenulation cleavage. Field width

~4 mm. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag.


Figure 23-33. Illustration of an Al2SiO5 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.


Figure 23-41. 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.


Figure 23-52. 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.

aa bb

Metamorphic Textures Textures of Regional Metamorphism F Dynamothermal (crystallization under...

Documents

Transcript of Metamorphic Textures Textures of Regional Metamorphism F Dynamothermal (crystallization under...