Chapter 6: Metamorphism: Alteration of Rocks By Temperature and Pressure

Question 1

What is the parent rock of marble?

Answer 1

Limestone

Question 2

What is the metamorphosed rock from limestone?

Answer 2

Marble

Question 3

What is the parent rock of schist?

Answer 3

Shale

Question 4

What is the metamorphosed rock from shale?

Answer 4

Schist

Question 5

Exhume

Answer 5

To transport to the Earth’s surface

Question 6

3 principal factors of metamorphism

Answer 6

Heat, pressure, fluid composition

Question 7

Average rate that temp increases with depth in the crust

Answer 7

30 deg C/km

Question 8

Geothermal gradient

Answer 8

The increase in temp with increasing depth in Earth’s interior

Question 9

Geothermometer

Answer 9

A rock’s mineral composition, which determines the temperature at which the rock formed (because different minerals form at different temperatures).

Question 10

2 plate tectonic mechanisms that form most metamorphic rocks

Answer 10

• subduction

* continent-continent collisions

Question 11

2 kinds of pressure (stress) rocks are subjected to

Answer 11

• confining pressure

* directed pressure/differential stress

Question 12

confining pressure

Answer 12

general force applied equally in all directions

Question 13

directed pressure/differential stress

Answer 13

force exerted in a particular direction

Question 14

Rate that pressure increases with depth in the crust

Answer 14

.3 to .4 kbars (kilobars) per km (300-400 bars/km)

Question 15

geobarometers

Answer 15

Mineral assemblages that can be used as pressure gauges, to determine the pressure that the rock formed

Question 16

metasomatism

Answer 16

A change in rock’s composition by fluid transport of chemical substances into or out of it

Question 17

6 types of metamorphism

Answer 17

• regional
• contact
• seafloor
• high-pressure
• burial
• shock

Question 18

regional metamorphism

Answer 18

• takes place where both high temps and pressures are imposed over large parts of the crust
• characteristic of convergent plate boundaries
• most widespread type

Question 19

contact metamorphism

Answer 19

• heat from an igneous intrusion metamorphoses the rock immediately surrounding it, normally only affecting a thin zone of country rock
• heat is from intruding magma
• pressure only relevant where intrusion is at great depths

Question 20

seafloor metamorphism

Answer 20

• associated with mid-ocean ridges

* hot lava heat sea water which circulates though the new ocean crust by convection; hot temperature alters the basalts

Question 21

burial metamorphism

Answer 21

• affects a smaller amount of rock
• low-grade metamorphism caused by the progressive increase of pressure and temperature exerted by the growing layers of overlying sediments and rock
• begins at 6-10 km

Question 22

high-pressure metamorphism

Answer 22

• pressures 8-12 kbars
• form at very low depths and take a long time to recycle to the surface
• most form in subduction zones as sediments scraped from oceanic crust and subducted to depths over 30 km

Question 23

shock metamorphism

Answer 23

• occurs when a meteorite collides with Earth

* mass and velocity is transformed into heat and shock waves through the country rock

Question 24

foliation

Answer 24

• a set of flat or wavy parallel cleavage planes produced by deformation of igneous and sedimentary rocks under directed pressure
• the most prominent textural feature of regionally metamorphosed rocks

Question 25

as the grade of regional metamorphism increases, foliation becomes more or less pronounced

Answer 25

more

Question 26

4 main criteria for classifying foliated rocks

Answer 26

* metamorphic grade * grain (crystal) size * type of foliation * banding

Question 27

progression of 5 foliated rocks (lowest grade to highest grade)

Answer 27

``` 1 - slate 2 - phyllite 3 - schist 4 - gneiss 5 - migmatite ```

Question 28

slate

Answer 28

* lowest grade of foliated metamorphosed rock * formed from shales or volcanic ash deposits * have strong foliation planes to split the rock

Question 29

phyllite

Answer 29

* foliated rock | * similar in character and origin to slate, but have a more glossy sheen from mica and chlorite

Question 30

schist

Answer 30

* foliated rock * characterized by schistosity: coarse, wavy foliation of lighter and darker bands * among the most abundant metamorphic rock types

Question 31

gneiss

Answer 31

* foliated rock * light colored rock with coarse bands of light and dark minerals throughout * gneissic foliation is from segregation of light-colored quartz and feldspar from darker amphiboles and other mafic minerals * poor foliation

Question 32

migmatite

Answer 32

* foliated rock * mixture of igneous and metamorphic rock * higher temperatures begin to melt a part of the country rock, creating the igneous portions

Question 33

granoblastic rocks

Answer 33

* nonfoliated metamorphic rocks that grow in equant shapes like cubes and spheres instead of platy or elongated * form where directed pressure is absent, so no foliation occurs * defined by mineralogy (because texture is homogeneous and granular)

Question 34

hornfels

Answer 34

* granoblastic rock * high-temperature contact metamorphic rock * uniform grain size with little or no deformation * formed from fine-grained sedimentary and other sliicate rocks

Question 35

quartzite

Answer 35

* granoblastic rock * some are homogeneous, some have bands of slate or schist * formed from quartz-rich sandstones

Question 36

marbles

Answer 36

* granoblastic rock * some are pure white and uniform crystals, some have bands of impurities from silicates and other minerals in the limestone * formed from limestone and dolomites

Question 37

greenstones

Answer 37

* granoblastic rock * many formed by seafloor metamorphism * abundance of chlorite gives the greenish cast * formed from volcanic rock

Question 38

amphibolites

Answer 38

* granoblastic rock * med- to high-grade metamorphism of mafic volcanic rocks * formed from amphibole and plagioclase feldspar

Question 39

granulite (granofels)

Answer 39

* granoblastic rock * homogeneous medium- to coarse-grained texture * formed from shale, impure sandstone, and many kinds of igneous rock

Question 40

porphyoblasts

Answer 40

* large crystals formed in a much finer-grained matrix of other minerals * formed by contact and regional metamorphism

Question 41

zeolite minerals

Answer 41

* form at low temps and pressures | * contain water within crystal structures

Question 42

metamorphic facies

Answer 42

grouping of rocks of various mineral compositions formed under different grades of metamorphism from different parent rocks