Metamorphic Textures Textures of Regional MetamorphismChapter 23: Metamorphic TexturesSlide 3Slide 4Dislocations in the crystal latticePowerPoint PresentationSlide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Analysis of Deformed RocksSlide 28Slide 29Slide 30Slide 31Sense of shear indicatorsMetamorphic TexturesMetamorphic TexturesTextures of Regional MetamorphismTextures of Regional Metamorphism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 EventsIt’s your task to unravel the complex history of these rocks...It’s your task to unravel the complex history of these rocks...Chapter 23: Metamorphic Textures Chapter 23: Metamorphic Textures TexturesTextures are small-scale penetrative features are small-scale penetrative featuresRelict TexturesRelict TexturesInherited from original rockInherited from original rock““Blasto-” = relict Blasto-” = relict Any degree of preservationAny degree of preservationPseudomorphs of minerals or pre-Pseudomorphs of minerals or pre-metamorphic textures/structuresmetamorphic textures/structuresChapter 23: Metamorphic Textures Chapter 23: Metamorphic Textures Metamorphic TexturesMetamorphic TexturesThe Processes of Deformation, Recovery, and The Processes of Deformation, Recovery, and RecrystallizationRecrystallization2.2.Pressure SolutionPressure SolutionFigure 23-2 a. Highest strain in areas near grain contacts (hatch pattern). b. High-strain areas dissolve and material precipitates in adjacent low-strain areas (shaded). The process is accompanied by vertical shortening. c. Pressure solution of a quartz crystal in a deformed quartzite (1 is vertical). Pressure solution results in a serrated solution surface in high-strain areas (small arrows) and precipitation in low-strain areas (large arrow). ~ 0.5 mm across. The faint line within the grain is a hematite stain along the original clast surface. After Hibbard (1995) Petrography to Petrogenesis. Prentice Hall.Chapter 23: Metamorphic Textures Chapter 23: Metamorphic Textures Figure 23-4 a. Undulose extinction and Undulose extinction and (b)(b) elongate subgrains in quartz due to dislocation formation and migrationelongate subgrains in quartz due to dislocation formation and migration Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.aabbDislocations in the crystal latticeDislocations in the crystal latticeFigure 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).Recrystallization by grain boundary migration Recrystallization by grain boundary migration and sub-grain rotationand sub-grain rotationFigure 23-6. Recrystallization by (a) grain-boundary migration (including nucleation) and (b) subgrain rotation. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag. Berlin. Figure 23-7a. Recrystallized quartz with irregular (sutured) boundaries, formed by grain boundary migration. Width 0.2 mm. From Borradaile et al. (1982).High-Strain Metamorphic Textures (shear zones)High-Strain Metamorphic Textures (shear zones)Figure 22-2. Schematic cross section through a shear zone, showing the vertical distribution of fault-related rock types, ranging from non-cohesive gouge and breccia near the surface through progressively more cohesive and foliated rocks. Note that the width of the shear zone increases with depth as the shear is distributed over a larger area and becomes more ductile. Circles on the right represent microscopic views or textures. From Passchier and Trouw (1996) Microtectonics. Springer-Verlag. Berlin.aabbFigure 23-15. Progressive mylonitization of a granite. From Shelton (1966). Geology Illustrated. Photos courtesy © John Shelton.ddccFigure 23-15. Progressive mylonitization of a granite. From Shelton (1966). Geology Illustrated. Photos courtesy © John Shelton.The Crystalloblastic SeriesThe Crystalloblastic SeriesMost EuhedralMost EuhedralTitanite, rutile, pyrite, spinelTitanite, rutile, pyrite, spinelGarnet, sillimanite, staurolite, Garnet, sillimanite, staurolite, tourmalinetourmalineEpidote, magnetite, ilmeniteEpidote, magnetite, ilmeniteAndalusite, pyroxene, amphiboleAndalusite, pyroxene, amphiboleMica, chlorite, dolomite, kyaniteMica, chlorite, dolomite, kyaniteCalcite, vesuvianite, scapoliteCalcite, vesuvianite, scapoliteFeldspar, quartz, cordieriteFeldspar, quartz, cordieriteLeast EuhedralLeast Euhedral Differences in development of crystal form among some metamorphic minerals. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco.Depletion haloesDepletion haloesProgressive development of a depletion halo about a growing porphyroblast. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco. Figure 23-13. Light colored depletion haloes around cm-sized garnets in amphibolite. Fe and Mg were less plentiful, so that hornblende was consumed to a greater extent than was plagioclase as the garnets grew, leaving hornblende-depleted zones. Sample courtesy of Peter Misch. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Progressive syntectonic metamorphism of a volcanic graywacke, New Zealand. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco.Progressive syntectonic metamorphism of a volcanic graywacke, New Zealand. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco.Progressive syntectonic metamorphism of a volcanic graywacke, New Zealand. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco.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