This document discusses metamorphism and metamorphic rocks. It begins by defining metamorphism as the change in form of rocks due to heat, pressure, and chemically active fluids. This causes changes in mineralogy, texture, and composition. The main factors that cause metamorphism are then discussed, including temperature, pressure (both uniform and direct), and chemically active fluids. Different types of metamorphism are also summarized, such as contact metamorphism near igneous intrusions and regional metamorphism during mountain building. The document concludes by noting how metamorphic rocks are eventually exhumed to the surface through erosion.
Definition, metamorphism.
limits and type of metamorphic agents.
Metamorphic processes.
Types of Metamorphism
Classification of metamorphic rocks and textures of metamorphic rocks
Mineral assemblages and Metamorphic grade and facies of metamorphic rocks.
Graphic representation of metamorphic mineral parageneses.
Bowen’s Reaction Series
ROCKS:
There are three kinds of rocks, that are defined on the basis of how they formed.
Igneous Rocks:
are formed from the solidification of molten rock or magma.
Sedimentary Rocks:
form through when materials at the earth's surface (sediments) are buried and hardened (lithified).
Metamorphic Rocks:
are formed when older rocks are changed by heat and pressure without being melted.
Definition, metamorphism.
limits and type of metamorphic agents.
Metamorphic processes.
Types of Metamorphism
Classification of metamorphic rocks and textures of metamorphic rocks
Mineral assemblages and Metamorphic grade and facies of metamorphic rocks.
Graphic representation of metamorphic mineral parageneses.
Bowen’s Reaction Series
ROCKS:
There are three kinds of rocks, that are defined on the basis of how they formed.
Igneous Rocks:
are formed from the solidification of molten rock or magma.
Sedimentary Rocks:
form through when materials at the earth's surface (sediments) are buried and hardened (lithified).
Metamorphic Rocks:
are formed when older rocks are changed by heat and pressure without being melted.
How can minerals deposits be formed; GEOLOGICAL PROCESSES; Ore Fluids; Ore Forming Processes; Concentrating Processes; Magmatic mineral deposits; Residual mineral deposits ; Placer deposits; Sedimentary mineral deposits; Metamorhogenic mineral deposits; Hydrothermal mineral deposits ; Magmatic Deposits
Cumulate deposits: fractional crystallization processes can concentrate metals (Cr, Fe, PGE, Pt, Ni, Ti, Diamond ))
Pegmatites : late staged crystallization forms pegmatites and many residual elements are concentrated (Li, Ce, Be, Sn, U, Rare Earths (REE), Feldspar, Mica, Gems).
magmatic deposits; Mode of Formation of Magmatic Ores Deposits; Mode of Formation of Orthomagmatic Ores ; Fractional Crystallization (or Crystal fractionation ); Magmatic (or Liquid ) Immiscibility; Simple crystallization without concentration (Dissemination); Segregation of early formed crystals; (Layer Types); Injection of material concentrated elsewhere by differentiation Residual liquid segregation; Residual liquid injection; Immiscible liquid segregation; Immiscible-liquid-injection; Early magmatic deposit; Late magmatic deposit; Types of Magmatic Ore Deposits:Chromite; Fe-Ti (± V) oxides; Ni – Cu – Fe (± Pt) sulfides; Platinum Group Elements (PGEs); REE, and Zr in Carbonatites; Diamond in kimberlites.
How can minerals deposits be formed; GEOLOGICAL PROCESSES; Ore Fluids; Ore Forming Processes; Concentrating Processes; Magmatic mineral deposits; Residual mineral deposits ; Placer deposits; Sedimentary mineral deposits; Metamorhogenic mineral deposits; Hydrothermal mineral deposits ; Magmatic Deposits
Cumulate deposits: fractional crystallization processes can concentrate metals (Cr, Fe, PGE, Pt, Ni, Ti, Diamond ))
Pegmatites : late staged crystallization forms pegmatites and many residual elements are concentrated (Li, Ce, Be, Sn, U, Rare Earths (REE), Feldspar, Mica, Gems).
magmatic deposits; Mode of Formation of Magmatic Ores Deposits; Mode of Formation of Orthomagmatic Ores ; Fractional Crystallization (or Crystal fractionation ); Magmatic (or Liquid ) Immiscibility; Simple crystallization without concentration (Dissemination); Segregation of early formed crystals; (Layer Types); Injection of material concentrated elsewhere by differentiation Residual liquid segregation; Residual liquid injection; Immiscible liquid segregation; Immiscible-liquid-injection; Early magmatic deposit; Late magmatic deposit; Types of Magmatic Ore Deposits:Chromite; Fe-Ti (± V) oxides; Ni – Cu – Fe (± Pt) sulfides; Platinum Group Elements (PGEs); REE, and Zr in Carbonatites; Diamond in kimberlites.
1- INTRODUCTION In any introductory textbook on physical geology- the.pdfcontact28
1. INTRODUCTION In any introductory textbook on physical geology, the reader will find the
discussion on metamorphic rocks located after the chapters on igneous and sedimentary rocks,
and for very good reason. Metamorphic rocks form by the physical and sometimes chemical
alteration of a pre-existing rock, whether it is igneous or sedimentary. In some cases, even
metamorphic rocks can be altered into a completely different metamorphic rock. With igneous
rocks forming from the melt produced by any rock type and a sedimentary rock forming from the
weathered product of any rock type, the alteration of any rock to produce a metamorphic one
completes the components of what is known as the rock cycle. Basically, the rocks we encounter
today that we classify as either igneous, metamorphic, or sedimentary, could have belonged to a
different rock classification in the past, as rocks are recycled throughout geologic time, driven by
the motion of the tectonic plates. It is easy to see that increasing the temperature of a rock can
produce magma, and that rocks on the surface of the earth can break up into sediment that can
ultimately lithify into a sedimentary rock. But how can we alter a solid rock into a new rock,
without melting it or making it become sediment? All rocks are formed at certain temperatures
and pressures on or more commonly, beneath the earth's surface, and these rocks are the most
stable at the conditions under which they form. Therefore, changing the temperature and/or
pressure conditions may lead to a different rock, one that changed in order to be stable under new
extemal conditions. This new rock that forms in response to changes in its physical and chemical
environment is called a metamorphic rock; the word metamorphism means to change form, and
for rocks this means a recrystallization of minerals (crystals) under subsolidus (temperatures too
low for melt production) conditions. A metamorphic change can also occur if the rock's
composition is altered by hot, chemically reactive fluids, causing a change in the mineral content
of the rock. To distinguish between the pre-existing rock and the new metamorphic one, the term
protolith or parent rock is used to describe the pre-existing rock, and all metamorphic rocks have
at least one protolith that has altered during metamorphism. In this chapter you will learn that all
metamorphic rocks are identified by the mineral content and texture of the rock; for metamorphic
rocks, texture refers to the orientation of the minerals in the rock, although crystal size does
convey important information regarding the temperature conditions during metamorphism. To
summarize, metamorphism is the process by which a pre-existing rock (the protolith) is altered
by a change in temperature, pressure, or by contact with chemically reactive fluids, or by any
combination of these three parameters. The alteration process is a recrystallization event, where
the initial rock's minerals (crystals) have changed size.
The mineralogical and structural adjustment of solid rocks to physic.pdfanubhavnigam2608
The mineralogical and structural adjustment of solid rocks to physical and chemical conditions
that have been imposed at depths below the near surface zones of weathering and diagenesis and
which differ from conditions under which the rocks in question originated.
The word \"Metamorphism\" comes from the Greek: meta = change, morph = form, so
metamorphism means to change form. In geology this refers to the changes in mineral
assemblage and texture that result from subjecting a rock to conditions such pressures,
temperatures, and chemical environments different from those under which the rock originally
formed.
There are two major kinds of metamorphism: regional and contact.
Regional metamorphism. Most metamorphic rocks are the result of regional metamorphism (also
called dynamothermal metamorphism). These rocks were typically exposed to tectonic forces
and associated high pressures and temperatures. They are usually foliated and deformed and
thought to be remnants of ancient mountain ranges.
Contact metamorphism. Contact metamorphism (also called thermal metamorphism) is the
process by which the country rock that surrounds a hot magma intrusion is metamorphosed by
the high heat flow coming from the intrusion. The zone of metamorphism that surrounds the
intrusion is called the halo (or aureole) and rarely extends more than 100 meters into the country
rock. Geostatic pressure is usually a minor factor, since contact metamorphism generally takes
place less than 10 kilometers from the surface.Metamorphism is defined as follows:
The mineralogical and structural adjustment of solid rocks to physical and chemical conditions
that have been imposed at depths below the near surface zones of weathering and diagenesis
and which differ from conditions under which the rocks in question originated.
The word \"Metamorphism\" comes from the Greek: meta = change, morph = form, so
metamorphism means to change form. In geology this refers to the changes in mineral
assemblage and texture that result from subjecting a rock to conditions such pressures,
temperatures, and chemical environments different from those under which the rock originally
formed.
There are two major kinds of metamorphism: regional and contact.
Regional metamorphism. Most metamorphic rocks are the result of regional metamorphism
(also called dynamothermal metamorphism). These rocks were typically exposed to tectonic
forces and associated high pressures and temperatures. They are usually foliated and deformed
and thought to be remnants of ancient mountain ranges.
Contact metamorphism. Contact metamorphism (also called thermal metamorphism) is the
process by which the country rock that surrounds a hot magma intrusion is metamorphosed by
the high heat flow coming from the intrusion. The zone of metamorphism that surrounds the
intrusion is called the halo (or aureole) and rarely extends more than 100 meters into the
country rock. Geostatic pressure is usually a minor factor, since contact metamorp.
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2. 1.Introduction
2.Metamorphism
3.Common Structures and Textures of Metamorphic
Rocks
4.Classification of Metamorphic Rocks
5.Descriptive Study of Common Metamorphic
Rocks (Quartzite, Marble, Slate, Gneiss, Schist).
AsifHasan
3. Metamorphic rocks are
geologically classified as
one of the major group of
rocks which have been
formed out of
metamorphism of
preexisting igneous and
sedimentary rocks.
Igneous Sedimentary
Metamorphic
AsifHasan
4. They are altered or changed beyond their recognition, i.e.
change in Chemical composition, texture and structure
When rocks are baked by heat or molten magma,
squeezed by the movements of huge tectonic plates or by
the pressure of overlying thick succession of rocks
AsifHasan
5. The word metamorphism means change of form (meta=
change; morph= form). In petrology, it indicates the effect
of temperature, pressure and chemically active solutions
over the texture, minerals and composition of parent
rocks.
This means the constituent minerals, texture and
composition of parent rocks by metamorphism change
over to new minerals or new texture or new composition
which are more stable and suitable under new condition.
For example, As a result of metamorphism Granite
changes to gneiss, sandstone changes to quartzite,
limestone changes to marble.
AsifHasan
6. There are six major factors in metamorphism:
Chemical composition.
The change in temperature.
The change in pressure.
The presence or absence of fluids.
How long a rock is subjected to high pressure or high
temperature.
Whether the rock is simply compressed or is twisted
and broken during metamorphism.
Factors in Metamorphism
AsifHasan
7. Metamorphic Agents
1. High Temperature
2. High Pressure
3. Chemically Active Fluids
The process of metamorphism occur in rocks due to effect of
high temperature, pressure and chemically active fluids.
These three are known as metamorphic agents. Generally, all
these three act together and cause metamorphism. But
sometimes, any one or two of them dominate and play an
active role.
AsifHasan
8. Temperature: The source of temperature which is
responsible for metamorphism is either due to depth or due
to the contact with magma. The metamorphic changes
mainly take place in the temperature range of 200 – 850 ° C.
The temperature rise also increases the chemical activity in
rocks and facilitates reaction during metamorphism.
AsifHasan
9. Pressure: The pressure which causes metamorphism is of two
different kind namely
1. Uniform pressure
2. Direct pressure
Uniform pressure: increases with depth. It acts vertically
downwards and affects the volume of both liquids and solids.
Naturally, its effect is significant only at great depths. But not at or
near the surface. This also means that high temperature will also be
associate with high temperature will also be associated with high
uniform pressure. So, both of them act together and bring about
metamorphism.
Direct pressure: which is also called stress, is due to tectonic
forces. Such pressure act in any direction, i.e. upward or downward
or sideward It acts only on solids and affect the shape of rocks or
minerals. It is effective in the upper layers of the crust and increases
with depth to some extent . The application of stress gives rise to
shearing movements in the rock and produces new minerals which
have platy habit and arranges approximately parallel to each other.
AsifHasan
11. UNIFORM PRESSURE
Types of Pressure
increases with depth due to
increase in overburden.
acts vertically downwards and
affects the volume of both liquid &
solids.
increases with depth up to some
extent, effective in the upper part of the
crust.
DIRECT or Differential PRESSURE
acts in all direction and affects only on
solids resulting into deformation of
shape and change in mineral
composition
High temperature is also associated
due to depth factor high temperature is not always
associated. to (depth factor)
Lithostatic pressure- due to
overburden Stress- due to tectonic forces
AsifHasan
12. Chemically Active Fluids:
play a key role in different ways in causing metamorphism.
First, since metamorphism of any type cannot take place for the
solid minerals in a perfect dry state, the presence of a liquid
medium of some kind is indispensable. Thus the liquids act as a
carrier of chemical components that actually take part in
chemical reaction. In other words, liquids provide the necessary
medium and facilitates the reaction to take place. The most
common liquid which play such role is water.
Second, the huge quantity of volatiles that are associated with
magmatic bodies ultimately permeate through the surrounding
rocks by means of diffusion and cause compositional changes
even in rocks. Far from magma.
Third, the magma or the hot juvenile hydrothermal solutions may
react directly with those rocks with which they come in contact.
AsifHasan
13. Metamorphic change occurs slowly in the solid state.
Several processes are at work.
Metamorphic Processes
Recrystallization – Minerals change size and shape.
Phase change – New minerals form with
Same chemical formula.
Different crystal structure.
Example: Andalusite to kyanite.
AsifHasan
14. Neocrystallization – New minerals with changes in
temperature and pressure.
Initial minerals become unstable and change to new
minerals.
Original protolith minerals are digested in reactions.
Elements restructure to form new minerals.
In this way, a shale can transform into a garnet mica
schist.
AsifHasan
15. Pressure solution – Mineral grains partially dissolve.
Dissolution requires small amounts of water.
Minerals dissolve where their surfaces press together.
Ions from the dissolution migrate in the water film.
AsifHasan
16. Plastic deformation – Mineral grains soften and deform.
Requires elevated temperatures.
Rock is squeezed or sheared.
Minerals act like plastic, changing shape without
breaking.
AsifHasan
17. Metamorphic Grade
Prograde – Metamorphism via increasing T and P.
Common in rocks that are buried in orogenic belts.
Progressive changes.
Recrystallization causes mineral growth.
Neocrystallization results in new mineral
assemblages.
Mineral changes release water
AsifHasan
18. Example: Prograde metamorphism of a pelitic rock.
Low grade – Shale protolith.
Clays recrystallize into larger, aligned clays to yield a slate.
Clays neocrystallize into tiny, aligned micas in a phyllite.
Intermediate grade –
Micas recrystallize and grow large to form a schist.
New minerals grow in the schist.
High grade -
Micas decompose; elements recombine into new minerals.
Neocrystallization yields quartz and feldspars in a gneiss.
AsifHasan
20. Retrograde – Metamorphism via decreasing T and P.
Common in rocks that are brought from depth by erosion.
Accompanied by addition of H2O by hydrothermal fluids.
Many prograde rocks aren’t retrograded. Rocks at the surface
can preserve prograde conditions.
Metamorphic Grade
AsifHasan
21. Metamorphic Environments
Metamorphism occurs in different settings.
Different settings yield different effects via…
• Geothermal gradient.
• Differential stresses.
• Hydrothermal fluids.
These characteristics are governed by tectonics.
AsifHasan
22. Metamorphic Environments
The types (and settings) of metamorphism are –
Thermal – Heating by a plutonic intrusion.
Burial – Increases in P and T by deep burial in a basin.
Dynamic – Shearing in a fault zone.
Regional – P and T alteration due to orogenesis.
Hydrothermal – Alteration by hot-water leaching.
AsifHasan
23. Contact Metamorphism
Due to heat from magma invading host rock.
Creates zoned bands of alteration in host rock.
Called a contact (or metamorphic) aureole.
The aureole surrounds the plutonic intrusion.
Zoned from high-grade (near pluton) to low-grade
(far from pluton).
Grades of alteration form bands around the pluton.
• Bands range from highly altered to slightly altered.
• Analogous to changes in pottery with increased
heating.
The width of each aureole zone is due to…
• The size of the plutonic intrusion.
• The degree of metasomatism.
The dominant rock is hornfels.
AsifHasan
25. Burial Metamorphism
As sediments are buried in a sedimentary basin
• P increases because of the weight of the overburden.
• T increases because of the geothermal gradient.
Requires burial below diagenetic effects
• This is ~ 8–15 km depending on the geothermal
gradient.
AsifHasan
26. Dynamic Metamorphism
Breakage of rock by shearing at a
fault zone.
Fault location determines type of
alteration.
Shallow crust – Upper 10–15
km.
o Rocks behave in a brittle
fashion.
o Mineral grains crush-
forming fault breccia.
Deeper crust – Below 10–15
km.
o Rocks behave in a ductile
manner.
o Minerals smear like taffy to
form mylonite.
AsifHasan
27. Regional Metamorphism
Tectonic collisions deform huge “mobile belts.”
Directed compression thickens mountains.
Rocks caught up in mountain building are…
Heated via the geothermal gradient and
plutonic intrusions.
Squeezed and heated by deep burial.
Smashed and sheared by differential stresses.
Regional metamorphism creates foliated rocks.
This type of metamorphism is, by far, the most
important in terms of the amount of rock altered.
Collisional belts are often…
Thousands of km long.
Hundreds of km wide.
AsifHasan
29. Hydrothermal Metamorphism
Alteration by hot, chemically aggressive water.
A dominant process near mid-ocean ridge magma.
Cold ocean water seeps into fractured crust.
Heated by magma, this water then reacts with mafic
rock.
The hot water rises and is ejected via black smokers.
AsifHasan
30. Exhumation
How do metamorphic rocks return to the surface?
Exhumation is due to uplift, collapse, and erosion.
AsifHasan
31. Finding Metamorphic Rocks
Large regions of ancient high-grade rocks, called shields,
are exposed in continental interiors.
Shields are eroded remnants of orogenic belts.
• Shield rocks form the basement under sedimentary
cover.
AsifHasan