Bài giảng Metamorphic facies powerpoint

Metamorphic facies
Diagram showing metamorphic facies in
pressure- temperature space. The domain of
thegraph corresponds to circumstances within the Earth's crust and
upper mantle.
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Metamorphic facies

1-Eclogite

2-Blueschist

3-Greenschist

4-Prehnite-

5-Pumpellyite

6-Zeolite

7-Granulite

8-Amphibolite

9-Hornfels

10-Sanidinite
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Metamorphic facies

The metamorphic facies are groups of

mineral compositions in
metamorphic rocks, that are typical for a
certain field in pressure-temperature
space. Rocks which contain certain
minerals can therefore be linked to
certain tectonic settings.
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Historic definition

The metamorphic facies are groups of mineral compositions in
metamorphic rocks, that are typical for a certain field in pressure-
temperature space

The name facies was first used for specific
sedimentary environments in sedimentary rocks by Swiss geologist
Amanz Gressly in 1838.

Analogous with these sedimentary facies a number of metamorphic
facies were proposed in 1920 by Finnish petrologist Pentti Eskola.

Eskola's classification was refined in the 1970s by New-Zealand
geologist Francis John Turner.
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Underlying principles

The different metamorphic facies are defined by
the mineralogical composition of a rock. When
the temperature or pressure in a rock body
change, the rock can cross into a different facies
and some minerals become stable while others

become unstable or metastable
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Index minerals

Every metamorphic facies has some index minerals by
which it can be recognized.

Very typical index minerals are the polymorphs of
aluminosilicate (Al2SiO5, all are nesosilicates).
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
Metamorphic
facies and their
mineral
assemblages
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Zeolite facies (LP/LT)

The zeolite facies is the metamorphic facies
with the lowest metamorphic grade.

The facies is named for zeolites, strongly
hydrated tectosilicates

It can have the following mineral assemblages:

heulandite + analcime + quartz ±
clay minerals
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Prehnite-pumpellyite-facies (LP/LT)


The prehnite-pumpellyite facies is a little higher in pressure
and temperature than the zeolite facies

. The prehnite-pumpellyite is characterized by the mineral
assemblages

prehnite + pumpellyite + chlorite + albite + quartz
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Greenschist facies (MP/MT)
The greenschist facies is at medium pressure and
temperature.
The facies is named for the typical schistose texture
of the rocks and green colour of the minerals chlorite,
epidote and actinolite.
Characteristic mineral assemblages are:

chlorite + albite + epidote ± actinolite, quartz
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Amphibolite-facies (MP/MT-HT)

The amphibolite facies is a facies of medium pressure and
average to high temperature.

It is named after amphiboles that form under such
circumstances.

It has the following mineral assemblages:

hornblende + plagioclase ± epidote, garnet,

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Granulite facies (MP/HT)

The granulite facies is the highest grade of metamorphism at
medium pressure.

The depth at which it occurs is not constant.

A characteristic mineral for this facies and the pyroxene-
hornblende facies is orthopyroxene.

orthopyroxene + clinopyroxene + hornblende
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
The blueschist facies is at relatively low
temperature but high pressure, such as occurs in
rocks in a subduction zone.

The facies is named after the schistose character of
the rocks and the blue minerals glaucophane and
lawsonite. mineral assemblages:

glaucophane + lawsonite + chlorite + sphene ±
epidote
Blueschist facies (MP-HP/LT)
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Eclogite facies (HP/HT)

The eclogite facies is the facies at the highest pressure and high
temperature.


It is named for the metabasic rock eclogite.

The mineral assemblages:

omphacite + garnet ± kyanite, quartz,
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Albite-epidote-hornfels facies (LP/LT-MT)

The albite-epidote-hornfels facies is a facies at low pressure
and relatively low temperatures.

It is named for the two minerals albite and epidote, though
they are stable in more facies.

Hornfels is a rock formed in contact metamorphism, a
process that characteristically involves high temperatures
but low pressures/depths.

albite + epidote + actinolite + chlorite + quartz
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Hornblende-hornfels facies (LP/MT)

The hornblende-hornfels facies is a facies with the same
low pressures but slightly higher temperatures as the
albite-epidote facies.

Though it is named for the mineral hornblende,

The hornblende-hornfels facies has the following

mineral assemblages:

hornblende + plagioclase ± diopside,
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Pyroxene-hornfels facies (LP/MT-HT)

The pyroxene-hornfels facies is the contact-
metamorphic facies with the highest temperatures
and is, like the granulite facies

Characterized by the mineral orthopyroxene.

Mineral assemblages:

orthopyroxene + clinopyroxene + plagioclase ±
olivine or quartz
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Sanidinite facies (LP/HT)

The sanidinite facies is a rare facies of extremely high temperatures and low
pressure.

It can only be reached under certain contact-metamorphic circumstances.

Due to the high temperature the rock experiences partial melting and glass is
formed.

This facies is named for the mineral sanidine.

cordierite + mullite + sanidine + tridymite (often altered to quartz) + glass

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References

Eskola, Pentti Eelis, 1920: "The mineral facies of rocks"

Phillpots, Anthony R., 1990: Principles of Igneous and
Metamorphic Petrology

Duff, P. McL. D., 1996; Holmes' Principles of Physical
Geology

Visser, W.A., 1980; Geological Nomenclature

Metamorphic facies by Dave Waters
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
ABID ALI

Geologist From University of Sargodha

Pakistan



#no.0923346965614
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