Metamorphic Rocks

The term metamorphic is derived from the Latin term
meaning, "change of form". These rocks have been
altered while in their solid state as a response to the
environment.

Extreme circumstances of pressure and

temperature, or an introduction of certain chemicals, can
cause the existing rocks minerals to recrystallize, and
they may even become different minerals all together.

It

is important that you realize that the rock remains in its
solid state. Once a rocks minerals are melted, and then
recrystallize, the new material will be igneous.

All rocks can be metamorphosed

(even an existing

metamorphic rock), however, sedimentary rocks are
more easily changed. Because of this, most of the
discussion will deal with changes in sedimentary types.

METAMORPHIC TEXTURES

AND COMPOSITIONS

Texture

     The new metamorphic textures are of two types,
granular

(also non-foliated) where the grains are

equidimensional, and foliated where the minerals
are layered .

     

KINDS OF METAMORPHISM

Barrovian (" regional" ) and Contact („thermal”).

The Relationships

Between

Rock and Process

 

REGIONAL

The second type of metamorphic rock is usually the
result of extreme pressure rather than that of
temperature. These are known as regional metamorphic
rocks.

These are commonly associated with mountain

building events and are often associated with plate
boundaries at continental margins.

THERMAL metamorphism

X =Slight Metamorphism

X

=Intense Metamorphism

^

=Igneous rock

Heat is the primary cause of alteration in formation of metamorphic
rocks .

These are called thermal metamorphic rocks, or contact
metamorphic rocks.

This type is often associated with lava flows and shallow plutons
(igneous intrusions).

Because of the high heat, the rock surrounding the intrusion is often
altered.

The pressure involved with these situations is in many instances,
negligible.

Alteration of the rock is generally localized in what is known as a
metamorphic

aureole or halo.

Thermal

meta-

morphis

m

Another principle source of heat is the natural
increase in temperature as the depth increases.
This is known as the geothermal gradient.
The typical geothermal gradient is about 30
degrees per kilometer (85 degrees per mile).

Main types of metamorphic rocks

Łupek

Łupek fyllitowy

Łupek metamorficzny

gnejs

Hornfels

Kwarcyt

Marmur

Ł
u
P
e
k

i
l
a
s
t
y

Granit

Piaskowiec
kwarcowy

Wapień/ dolomit

Metamorphic Rock

Composition

Minerały skał metamorfocznych:

Epidot, chloryty, zeolity, granaty, kordieryt, sylimanit, andaluzyt, mikroklin

Skarns

Au, Cu, Fe, Mo, Sn, W, and Zn-Pb skarn deposits

As subordinate layers in the feldspar-poor felsic volcanic
rocks, there appear peculiar dark rocks which also are
the ore's host rock. These rocks are in the Persberg area
denoted 'skarn', a word which likely can be used as a
collective term for all such odd rocks occurring alongside
the ores." Tornebohm goes on to describe garnet-rich
"brunskarn" (brown skarn) and pyroxene-rich
"gronskarn" (green skarn).

E Antarctica

Ksenolit

Gnejs z reliktami
warstwowania skały
osadowej

E

Antarctica

Smużyste odmieszania minerałów
ciemnych
w gnejsie o teksturze granulanej

E Antarctica

A – magnetyt, smugi w
gnejsie

B – smużyste odmieszania
minerałów ciemnych

C – granat w smugach

B

C

A

Thermal

Metamorphis

m

calcite

CaCO

3

calcite
+brucite

CaCO

3

+ Mg(OH)

2

monticellite

CaMgSiO

4

idocrase

Ca

10

Mg

2

Al

4

Si

9

O

34

(OH)

4

grossularite - wollastonite - diopside

Ca

3

Al

2

Si

3

O

12

- CaSiO

3

-

CaMgSi

2

O

6

Examination of the progressive
sequence
of key minerals indicates
that metasomatism has occurred.

increasing stress

S Africa

Batolit granitowy
metamorfizuje
ciemne łupki ilaste

SEDIMENTARY TO METAMORPHIC

The following is a very general progression from

sedimentary rock to metamorphic rock based primarily

on pressure.

SURFACE

MUD

5 km DEEP

SHALE (sedimentary)

10 km DEEP

SLATE (low grade

metamorphic)

15 km DEEP

SCHIST (Garnet appears)

20 km DEEP

GNEISS (high grade

metamorphic)

25 km DEEP

HORNFELS (Cordierite

appears)

Regional

Metamorphism

The zones of metamorphism in the Scottish
Highlands

Chlorite

Zone (slates, phyllites, and schists)

quartz-albite-white mica-chlorite-microcline ± calcite

Biotite Zone (phyllites and schists)

quartz-albite-white mica-chlorite-biotite ± microcline ±calcite ±

epidote

Almandine (

Garnet)

Zone (phyllites and schists)

quartz-albite-white mica-biotite-

garnet ± chlorite

Staurolite

Zone (schists)

quartz-oligoclase-white mica-biotite-

garnet-staurolite

Kyanite

Zone (schists)

quartz-oligoclase-white mica-biotite-

garnet-kyanite ±staurolite

Sillimanite

Zone (schists and gneisses)

quartz-oligoclase-biotite-

sillimanite ± kyanite

± K-feldspar ± white mica

At the lowest grade, in the

Zeolite

Facies, assemblages are characterized by clay minerals.

kaolinite-illite-smectite-chlorite-quartz-analcite

At slightly higher-grade conditions, Zeolite Facies are replaced by Prehnite-Pumpellyite Facies.
As the P-T conditions increase, Greenschist Facies assemblages form.

white mica-chlorite-chloritoid-quartz-albite-magnetite-biotite-

epidote-garnet-pyrophyllite

Amphibolite Facies

white mica-chlorite-biotite-quartz-plagioclase-

garnet-magnetite-staurolite-ilmenite-kyanite-

sillimanite

Granulite Facies

biotite-

garnet-

sillimanite-K feldspar-andesine-quartz-cordierite-orthopyroxene-

sillimanite

-zircon

Additional minerals that may occur include

stilbite, calcite, stilpnomelane, actinolite and

hornblende

.

Epidot
Granaty
Silimani
t
Stauroli
t
Kordier
yt
aktynoli
t

Zagadnienia do

zapamiętania

• Scharakteryzuj rodzaje metamorfizmu

• Jakie zmiany mineralne zachodzą podczas

metamorfizmu ?

• Jakie nowe skały powstają w wyniku metamorfizmu ?

• Wymień kilka, a opisz dokładnie jeden minerał skał

metamorficznych

Adresy internetowe

http://www.cobweb.net/~bug2/rock5.htm

http://csmres.jmu.edu/geollab/Fichter/MetaRx/metasimp

le.html

http://geology.csupomona.edu/alert/metamorphic/metar

xs.htm