Chapter 8: Metamorphic Rocks

metamorphic rock definition

preexisting rock changes to another rock

What aspects of a metamorphic rock change?

mineralogy, texture, chemical composition

What causes the formation of metamorphic rock?

temperature and pressure changes

Many metamorphic reactions occur in the presence of

fluids

Possible original rocks

igneous, sedimentary, metamorphic

3 agents of metamorphism; How many agents are rocks subjected to during metamorphism?

heat, pressure, fluids; all three

Most important agent

heat

Two sources of heat

magma and geothermal gradient

Geothermal gradient

earth’s temp increasing with depth

Remineralization results in minerals that are…

stable under high temperature and pressure conditions

Confining pressure

stress is applied equally in all directions

differential stress

stress is applied unequally, predominates one direction

What are chemically active fluids composed of?

water, volatile components

The type of agent can aid in the recrystallization of minerals and can also transport mineral matter far distances

chemically active fluids

Metasomatism

chemical changes in rock due to active fluids

Regional sources of chemically active fluids

geysers, hot springs, mid ocean ridges

Localized sources of chemically active fluids

sedimentary rock pores, igneous rock fractures

T/F: Most metamorphic rocks have the same chemical composition as their parent rock

true

What does mineral makeup determine?

how much a metamorphic agent will cause change

Does contact metamorphism occur at high or low temperatures?

high

Where does contact metamorphism occur

margins of magmatic intrusion

Metamorphism produces a zone of alteration called an

aureole

Hydrothermal metamorphism takes place along

mid ocean ridges

During hydrothermal metamorphism, crustal rocks on continents can…

react with hot fluids from igneous intrusions

Hydrothermal vein deposits examples

gold, silver, copper

Burial metamorphism

sedimentary rock buried deep in the earth

During burial metamorphism, what is preserved?

original bedding, sedimentary structures

During burial metamorphism, what is partially altered?

mineralogy, texture

Regional metamorphism

rock changes underground from high pressure (and heat)

Regional metamorphism is caused by

convergent tectonic forces

Is original rock preserved or destroyed during regional metamorphism? Why?

destroyed, undergoes intense alteration

Cataclastic metamorphism

rocks crush and shear from tectonic movement

Cataclastic metamorphism is localized along

fault planes

Contact metamorphism

rocks come into contact with magma/heat

impact metamorphism

projectiles or meteorites hit earth

What does impact metamorphism leave behind?

What are the products of meteorites called?

craters; impactites

Metamorphic facies

rock types formed under different temp and pressure

The size, shape, and arrangement of mineral grains

texture

Planar arrangement of mineral grains in rocks

foliation

Examples of foliation

slaty cleavage, parallel alignment, banding

Platy minerals texture

flat, thin, sheet like

Platy minerals examples

chlorite, mica

Slaty cleavage definition

rocks that split into thin sheets

Ways foliation can form

Mineral realignment and rotation, diff stress, shearing

Foliation type

shearing

Foliation type

gneissic

Foliation type

flattened pebbles

“Impart foliation” meaning

give rocks a layered look

Parallel alignment of mica and chlorite impart foliation to

slate

How is slaty cleavage formed?

shale changes to slate from differential stress

At upper low-grade metamorphism:

slate converts to phyllite

When slate converts into phyllite, what changes?

increased luster, platy minerals grow larger

At higher temperatures and pressures of medium-grade metamorphism:

phyllite converts to schist

What happens to the size of mineral and platy when shale converts to schist?

they become bigger, visible to the eye

Identify

garnet mica schist

High grade metamorphism converts:

schist to gneiss

When shale becomes gneiss (gneiss in the image), what happens to the minerals?

light and dark minerals separate into stripes

What are the darks bands of gneiss composed of? How about the light bands?

mafic minerals; felsic minerals

At temperatures beyond 700 C, gneiss partially melts and forms

migmatite

In migmatite, felsic minerals _______ and mafic minerals __________

melt; remain solid

What does the softened rick from migmatite do?

contorts and deforms from differential stress

Hydrothermal metamorphism of ultramafic rocks form

serpentinite

Soapstone is formed from _______ and is composed of ____

hydrothermal metamorphism; talc

Greenschist is produced by _________ and occurs in _________

regional metamorphism; subduction zones

Amphibolites (hornblende) is formed from _________ metamorphism of __________ rocks

medium grade; mafic igneous

When long, thin crystals of amphiboles are aligned in the same direction, it is called:

lineation

Granulites form from _____________ metamorphism of _________ rocks

high/very high grade; mafic igneous

Granulites consist of

quartz, garnet, pyroxene, feldspar

Nonfoliated rocks examples

quartz, marble, hornfels

Nonfoliated metamorphic rocks lack ______ in metamorphism;

they form from _______ and _______ metamorphism

differential stress; contact, hydrothermal

Quartzite Forms From the Metamorphism of

quartz sandstone

Marble forms through metamorphism of

limestone

Hornfels result from contact metamorphism of

shale

Index minerals are indicators of

metamorphic conditions

Aluminum silicate minerals are good indicators of ________ in metamorphism

pressure and temperature