Field trip — Sat. March 18thEclogite formation along fractures — Gabbro was metastableChapter 22: A Classification of Metamorphic RocksChapter 22: Foliated Metamorphic RocksSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Chapter 22: Specific Metamorphic Rock TypesSlide 12PowerPoint PresentationSlide 14Metamorphic FaciesSlide 16Slide 17Slide 18Slide 19Slide 20Field trip — Sat. March 18thDriver who can take 3 passengers?Bring a pen, hand lens, lunch and water (~1L)Wear layers — prepare for wet, windy conditions…rain jacket, umbrella?, sweatshirt…Wear shoes with good tread…hiking boots, good tennis shoes, or wellies (your feet might get wet)Eclogite formationalong fractures —Gabbro was metastableGranulite-eclogite transitionBergen Arcs, NorwayChapter 22: A Classification of Metamorphic Rocks•Metamorphic rocks are classified on the basis of texture and composition (either mineralogical or chemical)•Unlike igneous rocks, which have been plagued by a proliferation of local and specific names, metamorphic rock names are surprisingly simple and flexible•May choose some prefix-type modifiers to attach to names if care to stress some important or unusual textural or mineralogical aspectsChapter 22: FoliatedMetamorphic Rocks•Foliation: and planar fabric element•Lineation: any linear fabric elements–They have no genetic connotations–Some high-strain rocks may be foliated, but they are treated separatelyChapter 22: FoliatedMetamorphic RocksCleavage–Traditionally: the property of a rock to split along a regular set of sub-parallel, closely-spaced planes–A more general concept adopted by some geologists is to consider cleavage to be any type of foliation in which the aligned platy phyllosilicates are too fine grained to see individually with the unaided eyeSchistosity–A preferred orientation of inequaint mineral grains or grain aggregates produced by metamorphic processes–Aligned minerals are coarse grained enough to see with the unaided eye–The orientation is generally planar, but linear orientations are not excluded Chapter 22: FoliatedMetamorphic RocksGneissose structure–Either a poorly-developed schistosity or segregated into layers by metamorphic processes–Gneissose rocks are generally coarse grained Chapter 22: FoliatedMetamorphic RocksFigure 22-1. Examples of foliated metamorphic rocks. a. Slate. b. Phyllite. Note the difference in reflectance on the foliation surfaces between a and b: phyllite is characterized by a satiny sheen. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.aabbSlate: compact, very fine-grained, metamorphic rock with a well-developed cleavage. Freshly cleaved surfaces are dull Phyllite: a rock with a schistosity in which very fine phyllosilicates (sericite/phengite and/or chlorite), although rarely coarse enough to see unaided, impart a silky sheen to the foliation surface. Phyllites with both a foliation and lineation are very common Chapter 22: FoliatedMetamorphic RocksFigure 22-1c. Garnet muscovite schist. Muscovite crystals are visible and silvery, garnets occur as large dark porphyroblasts. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Schist: a metamorphic rock exhibiting a schistosity. By this definition schist is a broad term, and slates and phyllites are also types of schists. In common usage, schists are restricted to those metamorphic rocks in which the foliated minerals are coarse enough to see easily in hand specimen. Chapter 22: FoliatedMetamorphic RocksFigure 22-1d. Quartzo-feldspathic gneiss with obvious layering. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Gneiss: a metamorphic rock displaying gneissose structure. Gneisses are typically layered (also called banded), generally with alternating felsic and darker mineral layers. Gneisses may also be lineated, but must also show segregations of felsic-mineral-rich and dark-mineral-rich concentrations. Chapter 22: FoliatedMetamorphic RocksSerpentinite: an ultramafic rock metamorphosed at low grade, so that it contains mostly serpentine.Greenschist/Greenstone: a low-grade metamorphic rock that typically contains chlorite, actinolite, epidote, and albite. Note that the first three minerals are green, which imparts the color to the rock. Such a rock is called greenschist if foliated, and greenstone if not. The protolith is either a mafic igneous rock or graywacke.Amphibolite: a metamorphic rock dominated by hornblende + plagioclase. Amphibolites may be foliated or non-foliated. The protolith is either a mafic igneous rock or graywacke.Chapter 22: SpecificMetamorphic Rock TypesBlueschist: a blue amphibole-bearing metamorphosed mafic igneous rock or mafic graywacke. This term is so commonly applied to such rocks that it is even applied to non-schistose rocks.Eclogite: a green and red metamorphic rock that contains clinopyroxene and garnet (omphacite + pyrope). The protolith is typically basaltic. Chapter 22: SpecificMetamorphic Rock TypesFigure 21-1. Metamorphic field gradients (estimated P-T conditions along surface traverses directly up metamorphic grade) for several metamorphic areas. After Turner (1981). Metamorphic Petrology: Mineralogical, Field, and Tectonic Aspects. McGraw-Hill.Fig. 25-3.Fig. 25-3. Temperature-Temperature-pressure diagram pressure diagram showing the three showing the three major types of major types of metamorphic metamorphic facies series facies series proposed by proposed by Miyashiro (1973, Miyashiro (1973, 1994). 1994). Winter Winter (2001) An (2001) An Introduction to Introduction to Igneous and Igneous and Metamorphic Metamorphic Petrology. Petrology. Prentice Hall.Prentice Hall.Metamorphic FaciesFig. 25-2.Fig. 25-2. Temperature-Temperature-pressure diagram pressure diagram showing the generally showing the generally accepted limits of the accepted limits of the various facies used in this various facies used in this text. Boundaries are text. Boundaries are approximate and approximate and gradational. The gradational. The “typical” or average “typical” or average continental geotherm is continental geotherm is from Brown and Mussett from Brown and Mussett (1993). (1993). Winter (2001) An Winter (2001) An Introduction to Igneous Introduction to Igneous and Metamorphic and Metamorphic Petrology. Prentice Hall.Petrology. Prentice Hall.Paired Metamorphic Belts of Japan•Table 25-1. The definitive mineral