Chapter 10: Metamorphism: New Rocks from Old La Pietra by Michelangelo, carved from Carrera marble © 2012 John Wiley & Sons, Inc. All rights reserved.
Learning Objectives What is metamorphism? Describe the conditions necessary for metamorphism. Metamorphic rock Identify the metamorphic products of shale and basalt. Metamorphic processes Describe different types of metamorphism and their tectonic settings. Metamorphic facies Describe metamorphic zones and the types of facies they produce. © 2012 John Wiley & Sons, Inc. All rights reserved.
What Is Metamorphism ? Metamorphism The mineralogical, textural, chemical, and structural changes that occur in rocks A result of exposure to elevated temperatures and/or pressure © 2012 John Wiley & Sons, Inc. All rights reserved.
What Is Metamorphism ? The Limits of Metamorphism Low-grade Rocks metamorphosed under temperature and pressure conditions up to 400°C and 400 MPa High-grade Rocks metamorphosed under temperature and pressure conditions higher than about 400°C and 400 MPa Figure 10.2 Temperature and pressure conditions for metamorphism © 2012 John Wiley & Sons, Inc. All rights reserved.
Temperature and pressure Figure 10.3 From shale to gneiss © 2012 John Wiley & Sons, Inc. All rights reserved. What Is Metamorphism ? Factors Influencing Metamorphism
What a Geologist Sees— At the roadside © 2012 John Wiley & Sons, Inc. All rights reserved.
What Is Metamorphism ? Pore fluid Pore fluids influence metamorphism. Pores are open spaces. Figure 10.4 Quartz vein © 2012 John Wiley & Sons, Inc. All rights reserved.
Figure 10.5 Effects of uniform and differential stress © 2012 John Wiley & Sons, Inc. All rights reserved. Stress Foliation A planar arrangement of textural features in a metamorphic rock Gives rock a layered or banded appearance What Is Metamorphism ? Factors Influencing Metamorphism
Foliation Slaty cleavage Foliation in low-grade metamorphic rocks that causes such rock to break into flat, plate like fragments Schistosity Foliation in coarse- grained metamorphic rocks Figure 10.6 Foliation under the microscope © 2012 John Wiley & Sons, Inc. All rights reserved. What Is Metamorphism ? Factors Influencing Metamorphism
What Is Metamorphism ? Figure 10.7 Slaty cleavage © 2012 John Wiley & Sons, Inc. All rights reserved.
Metamorphism and Billiards © 2012 John Wiley & Sons, Inc. All rights reserved.
Duration Rate of metamorphism © 2012 John Wiley & Sons, Inc. All rights reserved. What Is Metamorphism ? Factors Influencing Metamorphism
Metamorphic Rock Rock with Foliation Slate A very fine-grained metamorphic rock with slaty cleavage; the metamorphic product of shale Phyllite A fine-grained metamorphic rock with pronounced foliation, produced by further metamorphism of slate © 2012 John Wiley & Sons, Inc. All rights reserved.
Metamorphic Rock © 2012 John Wiley & Sons, Inc. All rights reserved. Figure 10.8 Schistosity versus slaty cleavage
Metamorphic Rock Figure 10.9 Metamorphism of basalt © 2012 John Wiley & Sons, Inc. All rights reserved.
Metamorphic Rock Figure 10.9 Metamorphism of basalt © 2012 John Wiley & Sons, Inc. All rights reserved.
Quartzite The product formed by recrystallization of sandstone Metamorphic Rock Rock Without Foliation Figure Nonfoliated metamorphic rocks: Quartzite © 2012 John Wiley & Sons, Inc. All rights reserved.
Marble The product formed by recrystallization of limestone Figure Nonfoliated metamorphic rocks: Marble Metamorphic Rock Rock Without Foliation
Metamorphic Processes Processes that cause changes in texture and mineral assemblages in metamorphic rock Mechanical deformation Grinding, crushing, bending and fracturing Figure Mechanical deformation © 2012 John Wiley & Sons, Inc. All rights reserved.
Metamorphic Processes Processes that cause changes in texture and mineral assemblages in metamorphic rock Chemical recrystallization Changes in mineral composition, growth of new minerals, recrystallization of old minerals, and changes in amount of pore fluid Typically caused by heating and squeezing of rock Figure Contact metamorphic © 2012 John Wiley & Sons, Inc. All rights reserved.
Metamorphic Processes Types of Metamorphism Regional metamorphism Metamorphism of an extensive area of the crust Associated with plate convergence, collision, and subduction Other types of metamorphism occasionally occur in geologic settings where high temperature and/or elevated pressure or stress exists. Figure Tectonics and metamorphism © 2012 John Wiley & Sons, Inc. All rights reserved.
Contact metamorphism Rocks are heated and chemically changed adjacent to an intruded body of hot magma. Burial metamorphism Occurs after diagenesis; is a result of the burial of sediments in deep sedimentary basins. Figure Quick pressure, slow heat © 2012 John Wiley & Sons, Inc. All rights reserved. Metamorphic Processes Types of Metamorphism
Figure Instantaneous metamorphism © 2012 John Wiley & Sons, Inc. All rights reserved. Metamorphic Processes Types of Metamorphism
Metasomatism The process whereby the chemical composition of a rock is altered by the addition or removal of material by solution in fluids: Frequently water or carbon dioxide Figure Metasomatism © 2012 John Wiley & Sons, Inc. All rights reserved. Metamorphic Processes Metasomatism
Metamorphic Facies Metamorphic facies The set of metamorphic mineral assemblages Form in rocks of different compositions Form under similar temperature and stress conditions Figure Regional metamorphism in Scotland © 2012 John Wiley & Sons, Inc. All rights reserved.
Metamorphic Facies Figure Metamorphic facies © 2012 John Wiley & Sons, Inc. All rights reserved.
Critical Thinking Compare the concept of metamorphic facies to that of sedimentary facies. In what ways are they similar? In what ways are they different? Museum curators obviously can’t shave off pieces from valuable art. How do you think they manage to identify the rocks and minerals? Briefly explain how pressure and temperature might change over time in rocks being subjected to contact, burial, and subduction-related regional metamorphism. © 2012 John Wiley & Sons, Inc. All rights reserved.