Physical Geology 101
16. Metamorphic Rocks II
(p. 233-242)
Causes of Metamorphism
The two main processes that occur within a rock during metamorphism are:

______________________: physical processes like squeezing and crushing
- caused by strong forces (causes a _____________)

______________________: changes in mineral chemistry / growth of new minerals
from old ones.
Can these two processes occur together at the same time?
YES or
NO
The six main driving mechanisms (types of metamorphism) for the above metamorphic processes are:

________________ metamorphism (aka _____________ metamorphism)

________________ metamorphism

________________ metamorphism

________________ metamorphism

________________ metamorphism (aka _____________ metamorphism)

________________ metamorphism along fault zones
1. Contact or Thermal Metamorphism
Contact metamorphism occurs around an ________________________.
The heat of the intrusion radiates out and metamorphoses the rocks in contact with the intrusion, called
host rocks or ______________________.
The region of metamorphosed rock around an intrusion is called an ________________.
Contact metamorphism occurs around all types of igneous intrusions, regardless of their size.
Examples: _______________________________________________________
Effect of intrusion size:
The larger the intrusion, the wider the zone of metamorphism around the intrusion. Batholiths can
metamorphose rocks over a distance of ____________ ____________________ away from the
batholith. Dikes and sills may only have aureoles _________________________ wide.
What other three factors may influence the size of an aureole?
1. ___________________________________
2. ___________________________________
3. ___________________________________
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Physical Geology 101
Which type of magma produces the widest aureoles, and why?
Type: ___________________
Reason: ___________________________________________________
Temperature is more of a factor than pressure around an intrusion. So which type of metamorphic
process is most commonly associated with contact metamorphism?
mechanical deformation
OR
mineral recrystallization?
So contact metamorphosed rocks usually don't have a foliation.
Typical metamorphic rock type produced: __________________
2. Hydrothermal Metamorphism
Many of the hot fluids, or ___________________________, coming off of a magma intrusion can cause
changes in the minerals in the surrounding rocks. This is called hydrothermal alteration.
This type of metamorphism, driven by fluids, is also called _______________________.
Environment where metasomatism commonly occurs: ________________________
Types of minerals that form here due to hydrothermal alteration:
__________________,
___________________,
and ___________________
Hydrothermal fluids may also carry metallic ions that precipitate valuable ore minerals in the rocks around
the intrusion. What are nine examples of these ore minerals?
1. _________________
2. _________________
3. _________________
4. _________________
5. _________________
6. _________________
7. _________________
8. _________________
9. _________________
3. Regional Metamorphism
How large of an area may be affected by regional metamorphism?
_____________________________
Regional metamorphism occurs at convergent plate boundaries where tectonic plates collide. What are
two characteristics of these types of locations?
1. ________________________
2. ________________________
The resultant metamorphic rocks form the deep cores of the mountains (e.g., the __________________).
The rocks are highly deformed and foliated, which tells us that strong forces must have been involved in
their creation.
So which type of metamorphic process is most commonly associated with regional metamorphism?
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Physical Geology 101
mechanical deformation
OR
mineral recrystallization?
What types of metamorphic rocks are associated with regional metamorphism?
_____________________
_____________________
_____________________
_____________________
4. Burial Metamorphism
Burial metamorphism occurs in regions where a lot of sedimentary rocks get piled on top of each other
inside a so-called ________________________. The rocks get buried deeper and deeper under the
weight of the rocks on top. These basins can extend down to depths of ______ km.
Initially the sediment undergoes diagenesis, turning the sediment into rock. Then, when the rocks get
buried to depths where the temperature exceeds _______C, burial metamorphism begins.
Typically, the metamorphic rocks so produced do not exhibit a foliation. So which type of metamorphic
process is most commonly associated with burial metamorphism?
mechanical deformation
or
mineral recrystallization?
5. Dynamic Metamorphism in Fault Zones
What does dynamic mean? ___________________________
This type of metamorphism results predominantly from large differential stresses within narrow zones of
deformation in the crust called fault zones or ___________________.
Near the surface, the deformation in fault zones is brittle and results in a highly fragmented rock called
fault breccia. Deeper down, where temperatures are higher, minerals recrystallize and get aligned parallel
to each other, producing a noticeable foliation. The type of fault rock produced is called
__________________.
What minerals are common in these rocks? _____________ and ________________.
Based on the strongly foliated rocks, which type of metamorphic process is most commonly associated
with dynamic metamorphism?
mechanical deformation
OR
mineral recrystallization?
6. Impact or Shock Metamorphism
This type of metamorphism is produced by the instantaneous spike in heat and pressure caused by the
collision of a rapidly moving projectile with the Earth.
These projectiles are called ______________________.
The types of impact-produced rocks that are created are called ___________________.
Mineral Assemblages and Metamorphic Grade
What are the three grades of metamorphism?
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Physical Geology 101
___________________ ,
______________________ and ___________________
Where contact metamorphism occurs around an igneous intrusion, the grade of metamorphism
_________________ as you get further and further away from the intrusion. This makes sense because
the rock temperature gradually gets less and less further away from the intrusion so the metamorphic
grade must decrease.
We see this change in metamorphic grade by the different combinations of metamorphic minerals present
in the rocks. Any particular combination of minerals is called a:
___________________________
At different distances from an intrusion, different combinations of minerals can be seen, even though the
original rock was the same at each point before metamorphism began. Each mineral assemblage is
characteristic of specific metamorphic conditions (grades).
Are the types of minerals that occur in each assemblage dependent on the type of rock being
metamorphosed?
YES or NO ?
Geologists have studied metamorphic rocks in great detail and have determined that specific
assemblages of minerals occur consistently when any particular rock type gets metamorphosed. These
mineral combinations are called:
_________________________
Example: if a clay-rich rock (e.g., shale) gets metamorphosed, the resultant rock contains the minerals
muscovite and chlorite. What do these minerals indicate about the grade of metamorphism? (choose
one)
Low grade
Intermediate grade
High grade
If muscovite and chlorite start to turn into the mineral biotite, what is the grade of metamorphism?
(choose one)
Low grade
Intermediate grade
High grade
If we have a metamorphosed clay-rich rock that contains the minerals garnet, staurolite, or sillimanite,
what is the grade of metamorphism? (choose one)
Low grade
Intermediate grade
High grade
For the same original rock type (like shale), the index minerals are always the same for a particular
metamorphic grade. This is why mineral assemblages in metamorphic rocks can tell us so much about
the conditions of metamorphism.
Do we see the same index minerals as in clay-rich rocks when we progressively metamorphose basalt to
higher and higher metamorphic grades?
YES
or
NO
?
We know exactly which mineral assemblages result from the metamorphism of specific rock types, so we
can always determine the grade of metamorphism by identifying the index minerals present in the rock.
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Physical Geology 101
What do we call lines on a geologic map that show the boundaries between the locations of different
grades of metamorphic rocks with different mineral assemblages?
______________________
Pressure and Temperature Ranges of Metamorphic Conditions
The full range of temperature and pressure conditions that control the grade of metamorphism for any
rock type can be divided up into a number of smaller divisions of discrete T and P ranges called
__________________________.
Metamorphic facies are just a more refined way of looking at metamorphic grade.
FINAL QUESTION:
What are the different types of metamorphic facies?
____________________
____________________
____________________
____________________
____________________
____________________
____________________
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