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Metamorphism: New Rocks from Old Chapter 10 Geology Today Barbara W. Murck, Brian J. Skinner N. Lindsley-Griffin, 1999 Disharmonic Folding in Gneiss.

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Presentation on theme: "Metamorphism: New Rocks from Old Chapter 10 Geology Today Barbara W. Murck, Brian J. Skinner N. Lindsley-Griffin, 1999 Disharmonic Folding in Gneiss."— Presentation transcript:

1 Metamorphism: New Rocks from Old Chapter 10 Geology Today Barbara W. Murck, Brian J. Skinner N. Lindsley-Griffin, 1999 Disharmonic Folding in Gneiss

2 Rock Cycle Metamorphic Rock Rock formed in the solid state by alteration of preexisting rock deep within the Earth. Heat, pressure, and chemically active fluids are the agents. J. R. Griffin, 1999

3 N. Lindsley-Griffin, 1999 Metamorphism Mineralogical, chemical, and structural changes in solid rocks, in response to physical and chemical conditions at depths below regions of sedimentation and diagenesis. Fig. 10.2, p. 273

4 N. Lindsley-Griffin, 1999 Metamorphism Pressure, temperature are the most important factors.

5 N. Lindsley-Griffin, 1999 PORE FLUIDS Small amounts of gases or liquids between grains Facilitate solution, migration, and precipitation of ions to speed up recrystallization Provide a reservoir for ions during the growth of new minerals Speed up reactions Fig. 10.3, p. 274 Metamorphic Factors Quartz veins in slate

6 N. Lindsley-Griffin, 1999 PRESSURE 1. Confining pressure: greater density, prevents fracture, plastic deformation 2. Differential stress: Non- uniform pressure produces preferred orientation, rock cleavage, foliation Fig. 10.4, p. 275: Metamorphic Factors Granite formed in uniform stress Gneiss formed in differential stress

7 N. Lindsley-Griffin, 1999 HEAT Enhances recrystallization Speeds up chemical reactions At deepest crustal levels, some of the rock melts Migmatite - part metamorphic and part igneous (Fig. 10.9, p. 281) Metamorphic Factors

8 N. Lindsley-Griffin, 1999 TIME - enhances all other metamorphic factors Long periods of time allow larger grains to grow SlateGneissProtolith: shale Low gradeHigh grade Metamorphic Factors

9 LARGE AMOUNTS OF FLUIDS = METASOMATISM Composition changes greatly by: - addition of new material - removal of old material - combination of both Fig , p. 291: Limestone changed into red garnet, green pyroxene, and calcite rock. If pure, would be marble. N. Lindsley-Griffin, 1999 Metamorphic Factors

10 LARGE AMOUNTS OF FLUIDS = METASOMATISM Composition changes greatly by: - addition of new material - removal of old material - combination of both Fig , p. 291: Limestone changed into red garnet, green pyroxene, and calcite rock. If pure, would be marble. N. Lindsley-Griffin, 1999 Metamorphic Factors

11 Preferred orientation: N. Lindsley-Griffin, 1998 All the seagulls are facing into or away from the wind This alignment produces a foliation

12 From conglomerate to metaconglomerate - flattened cobbles parallel to each other Foliation: N. Lindsley-Griffin, 1998 Metaconglomerate, Fig. 10.5, p. 276 Alluvial sandstone and conglomerate

13 Slaty cleavage - tendency to break along planes that form perpendicular to maximum stress. In folded layers the cleavage parallels the axial plane Foliation: N. Lindsley-Griffin, 1999 Slaty cleavage at angle to bedding Fig. 10.7, p. 277

14 Schistosity - planar minerals like mica crystallize perpendicular to maximum stress. Foliation: N. Lindsley-Griffin, 1999 Garnet Schist Thin section view of schistosity in phyllite

15 Gneiss - micaceous schist alternating with coarsely crystalline bands Pre-existing layers High-grade metamorphism Foliation: N. Lindsley-Griffin, 1999

16 Progressive changes to shale as higher T and P over time allow different index minerals to form. Fig. 10.8, p. 280 Low Grade to High Grade N. Lindsley-Griffin, 1999

17 Types of Metamorphism CONTACT METAMORPHISM Rocks are heated and chemically changed by intrusion of hot magma. Concentric zones or aureoles

18 N. Lindsley-Griffin, 1999 BURIAL METAMORPHISM - Deep sedimentary basins REGIONAL METAMORPHISM - Subduction and plate collision; most intense where continents collide Affects broad regions Mountain ranges and continental interiors Fig , p. 283 Types of Metamorphism

19 METASOMATISM Very large water-rock ratios Composition changes greatly by: - addition of new material - removal of old material - combination of both Fig , p. 291: Limestone changed into red garnet, green pyroxene, and calcite rock. If pure, would be marble. N. Lindsley-Griffin, 1999 Types of Metamorphism

20 N. Lindsley-Griffin, 1999 INDEX MINERAL - appears at certain P-T conditions in the progression from lower grade to higher grade: Chlorite Biotite Garnet Kyanite Sillimanite ISOGRADS - lines on map showing where a particular index mineral first appears. Fig , p. 284 Metamorphic Facies

21 Assemblage of minerals typical of a set of metamorphic conditions N. Lindsley-Griffin, 1999 Metamorphic Facies Fig , p. 285

22 Polymorphs of Al 2 SiO 5 reveal P-T conditions N. Lindsley-Griffin, 1999 Kyanite Andalusite Sillimanite Metamorphic Facies Fig , p. 285, with additions

23 Continental core regions -- Canadian Shield Regional metamorphism N. Lindsley-Griffin, 1998

24 Finely foliated rocks: slate and phyllite. Slate, with slaty cleavage at high angle to bedding N. Lindsley-Griffin, 1998 Regional metamorphism

25 Coarsely foliated rocks: Schist Micaceous minerals, formed from shale or siltstone N. Lindsley-Griffin, 1998 Regional metamorphism

26 Coarsely foliated rocks: Gneiss Bands of micaceous minerals alternating with bands of granular minerals (usually quartz and feldspar) N. Lindsley-Griffin, 1998 Regional metamorphism

27 Shear Metamorphism Along faults - grinding and crushing at shallow crustal levels, stretching and recrystallization at deeper levels. Also known as cataclastic metamorphism (not in textbook). Mylonite Thin section N. Lindsley-Griffin, 1998

28 Metamorphic Rocks Protolith + Process = Product Basalt + moderate T and P = greenschist (green chlorite) Basalt + high T and P = amphibolite (black amphibole) N. Lindsley-Griffin, 1999 Fig , p. 288 AmphiboliteGreenschist Foliated

29 Metamorphic Rocks Protolith + Process = Product Basalt + low T, high P = Blueschist (blue amphibole) Blueschist + high T and P = Eclogite (green pyroxene, red garnet) (Fig , p. 288) N. Lindsley-Griffin, 1999 Foliated

30 Metamorphic Rocks Protolith + Process = Product Shale Slate Phyllite Schist, Gneiss N. Lindsley-Griffin, 1999 Fig. 10.8, p. 280 Increasing metamorphic grade Foliated

31 Shale + heat, pressure Slate Phyllite with progressive growth of foliation, grain size (Fig , p. 287) Metamorphic Rocks Protolith + Process = Product N. Lindsley-Griffin, 1999 Foliated

32 Metamorphic Rocks Protolith + Process = Product Phyllite Schist (clay-rich) Gneiss (quartz + feldspar rich) N. Lindsley-Griffin, 1999 Foliated

33 Metamorphic Rocks Protolith + Process = Product Quartz sandstone + Recrystallization = Quartzite N. Lindsley-Griffin, 1999 Thin section of QuartziteHand specimen of Quartzite Fig , p. 290 Nonfoliated

34 Metamorphic Rocks Protolith + Process = Product Limestone + Recrystallization = Marble N. Lindsley-Griffin, 1999 Thin section of Marble Hand specimen of Marble Fig , p. 290 Nonfoliated

35 © Houghton Mifflin All rights reserved High pressure, low temperature in subduction zone Greenschist and Blueschist facies High temperature, low pressure in volcanic arcs Greenschist and Amphibolite facies Metamorphic Facies at Convergent Boundaries

36 © Houghton Mifflin All rights reserved Regional Contact Shear Metamorphism at Convergent Boundaries

37 © Houghton Mifflin All rights reserved Sea water circulates in fractures Water is heated, hydrothermally changes basalt Metals are concentrated near hot vents Metamorphism at Mid-Ocean Ridges

38 © Houghton Mifflin All rights reserved Divergent: Hydrothermal Shear Transform: Shear Metamorphism at Divergent and Transform Boundaries


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