Slide 1Regional Metamorphism (Dynamothermal) Related to Convergent TectonicsDeformation and MetamorphismSlide 4Classification of Deformational Foliation Cleavage and SchistosityDevelopment of Deformational FoliationSlide 7Crenulation Cleavage Multi-stage DeformationDevelopment of Deformational Foliation in Bedded Sedimentary RocksBedding – Cleavage IntersectionsTiming of Deformation and MetamorphismSlide 12Timing of New Mineral Growth Relative to Deformation Evidence from Inclusion-Bearing Porphyroblasts and PoikiloblastsTiming of New Mineral Growth Relative to DeformationSlide 15Slide 16Slide 17OROGENY LEADS TO POLYMETAMORPHISMGEOL 2312 IGNEOUS AND METAMORPHIC PETROLOGYLecture 22Textures of Regionally Metamorphosed RocksMarch 27, 2009REGIONAL METAMORPHISM(DYNAMOTHERMAL)RELATED TO CONVERGENT TECTONICSDEFORMATION AND METAMORPHISMOROGENESIS (Mountain Building)Multiple Tectonic Events Multiple Metamorphic CyclesEach composed of Multiple Each composed of multiple Deformational Events metamorphic reaction eventscaused by reorientation & caused by abrupt changes in intensity of Stresses Pressure and Temperature NOT ALWAYS 1 to 1 Correlationa. Compositional layeringb. Preferred orientation of platy mineralsc. Shape of deformed grainsd. Grain size variatione. Preferred orientation of platy minerals in a matrix without preferred orientationf. Preferred orientation of lenticular mineral aggregatesg. Preferred orientation of fracturesh. Combinations of the above Winter (2001) Figure 23-21. Types of fabric elements that may define a foliation. From Turner and Weiss (1963) and Passchier and Trouw (1996). Foliation, Layering, Lamination, and Other Planar FabricsDeformational foliation is a secondary feature of rocks referring to the planar alignment of elongate minerals resulting from strain imparted to a rockCLASSIFICATION OF DEFORMATIONAL FOLIATION CLEAVAGE AND SCHISTOSITYFigure 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.DEVELOPMENT OF DEFORMATIONAL FOLIATIONProposed mechanisms for the development of foliationa. Mechanical rotation. b. Preferred growth normal to compression. c. Grains with advantageous orientation grow whereas those with poor orientation do not (or dissolve). d. Minerals change shape by ductile deformation. e. Pressure solution. f. A combination of a and e. g. Constrained growth between platy minerals. h. Mimetic growth following an existing foliation. Winter (2001) Figure 23-27. Proposed mechanisms for the development of foliations. After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.DEVELOPMENT OF DEFORMATIONAL FOLIATIONWinter (2001) Figure 23-28. Development of foliation by simple shear and pure shear (flattening). After Passchier and Trouw (1996) Microtectonics. Springer-Verlag.CRENULATION CLEAVAGEMULTI-STAGE DEFORMATIONDEVELOPMENT OF DEFORMATIONAL FOLIATIONIN BEDDED SEDIMENTARY ROCKSBEDDING – CLEAVAGE INTERSECTIONSSandySandy(poorly foliated)(poorly foliated)Clayey(well foliated)TIMING OF DEFORMATION AND METAMORPHISMSuccessive dynamothermal events and microstructures are numbered:Metamorphic Events – M1, M2, M3, ...Deformational Events – D1, D2, D3, ...Foliation Orientations – S0, S1, S2, S3, ... (S0- primary feature)Lineation Orientations – L0, L1, L2, L3,...(L0- primary feature)Winter (2001) 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.TIMING OF DEFORMATION AND METAMORPHISMWinter (2001) 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.TIMING OF NEW MINERAL GROWTH RELATIVE TO DEFORMATIONEVIDENCE FROM INCLUSION-BEARING PORPHYROBLASTS AND POIKILOBLASTSPorphyroblast inclusions inherit Porphyroblast inclusions inherit the fabric of the host matrixthe fabric of the host matrixOrientation - SOrientation - SiiSiTIMING OF NEW MINERAL GROWTH RELATIVE TO DEFORMATIONPost-kinematic: Si is identical to and continuous with Se (external foliation)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.Pre-kinematic Pre-kinematic crystalscrystalsa.a.Bent crystal with Bent crystal with undulose extinctionundulose extinctionb.b.Foliation wrapped Foliation wrapped around a porphyroblastaround a porphyroblastc.c.Pressure shadow or Pressure shadow or fringefringed.d.Kink bands or foldsKink bands or foldse.e.MicroboudinageMicroboudinagef.f.Deformation twins Deformation twins 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 pseudomorphFigure 23-35. Typical textures of post-kinematic crystals. From Spry (1969) Metamorphic Textures. Pergamon. Oxford.Syn-kinematic crystalsSyn-kinematic crystalsWinter (2001) 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. Spiral PorphyroblastsOROGENY LEADS TO