Sp21_Lab8_Metamorphic-1
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University of North Carolina, Chapel Hill *
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Geology
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Apr 3, 2024
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GEOL 101L Lab 8: Metamorphic Rocks and Processes
Name: Date:
Introduction
Make sure you’ve watched the pre-lab video and have your notes handy. Also utilize the information on https://meg.georockme.com/home
. These materials/resources, along with the appendix will help you answer the question: How can we use a rock's color, texture, and other physical characteristics to figure out what a rock is composed of and how it formed?
The learning objectives for today are:
Students will be able to….
Describe how rocks can change as they are metamorphosed (Parts A and B)
Distinguish between types of metamorphic processes, conditions, textures, and rocks.
Rank degree of foliation using observations of metamorphic rocks
Identify the metamorphic rocks: slate, phyllite, schist, gneiss, marble, and quartzite based on textural and compositional observations. Materials:
Internet access
This lab
Pre-lab reading
Before you begin
Brainstorm with the people you’re working with….
1.
Differentiate between contact and regional metamorphism. b.
Where on or in Earth would contact metamorphism occur? What agent is primarily responsible
for the metamorphism: high temperature, high pressure or both?
Contact metamorphism occurs in the surrounding rocks in contact with an intrusive magma body; occurs primarily due to high temperature (pressure change is negligible I think)
.
c.
Where on or in Earth would regional metamorphism occur? What agent is primarily responsible for the metamorphism: high temperature, high pressure or both?
High pressure and temperature is responsible for regional metamorphism
. Regional metamorphism usually occurs at convergent boundaries.
2.
Foliated vs non-foliated metamorphic rocks
b.
Which agent of metamorphism (temperature or pressure) do you think is most important in determining if a metamorphic rock has a foliated texture? Why?
1
GEOL 101L Lab 8: Metamorphic Rocks and Processes
Name: Date:
In areas that have been regionally metamorphized, most likely will find foliated rocks because of the high pressure. More likely to find non-foliated rocks in areas contact metamorphized.
c.
What factors (aside from temperature and pressure) determine if a metamorphic rock has a foliated texture? Foliated rocks have mineral crystals aligned in planes or bands. If the protolith rock has flat, platy crystals, they can create foliations over round, blocky crystals.
Part A: Deformation Demonstration
View the instructor-led demo modeling the deformation of pennyite and clayorite. 3.
Pennyite contains flat, plate-shaped mineral crystals. In the video, you will see
pennyite undergoing ductile deformation with directional stress (more pressure
in one plane than others, see image).
b.
Before watching the video, hypothesize: how will the pennyite look
after deformation occurs? It would display foliations, and since pressure is horizontal, the rock would expand vertically.
c.
Recall the minerals you saw in Lab 6. Give an example of a mineral with relatively flat crystals. Biotite mica.
4.
Clayorite contains rounded or blocky crystals. In the video, you will see
clayorite undergoing ductile deformation with directional stress (more pressure
in one plane than others, see image).
b.
Before watching the video, hypothesize: how will the clayorite look
after deformation occurs? I hypothesize that clayorite would not display foliations, as it has round, blocky crystals.
It would still expand vertically to some degree because of pressure.
a.
Recall the minerals you saw in Lab 6. Give an example of a mineral with blocky crystals. Halite.
5.
Now watch the videos.
Sketch or describe how each rock appeared before and after deformation. Describe the changes you observed and what caused these changes to occur. Pennyite
Before
The rock is full of buttons, which are all facing After
The rock expanded vertically to horizontal 2
GEOL 101L Lab 8: Metamorphic Rocks and Processes
Name: Date:
different directions within the rock. The minerals are more platy.
pressure and the minerals within are all facing the same orientation.
Clayorite
Before
The rock is circular and has round, blunt minerals (pinto beans) evenly spread throughout. After
After horizontal pressure, the clayite expanded vertically. The orientation of the pinto beans are all in different directions (up, down, sideways)
Part B:
Metamorphism: What’s Happening?
You will observe two sets of rocks. Each set of rocks includes one or more metamorphic rocks and the sedimentary
parent rock.
A
parent rock
(or protolith) is the original rock from which a metamorphic rock was formed. A parent rock can be an igneous, sedimentary, or metamorphic rock. 6.
Shale is a sedimentary rock and is the parent rock (protolith) of slate, phyllite, and schist (all metamorphic). With your lab group, a.
Observe and discuss the changes that took place when the shale underwent metamorphism into slate, phyllite, and schist. Increasing grain size (reflects more light) and foliations were created.
b.
Additionally, hypothesize what caused these changes to occur. Provide your observations and hypothesis below. Increased temperature and pressure caused these changes to occur. This is an example of regional, not contact, metamorphism.
Images from . Please click on images to see more detail/zoom in.
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GEOL 101L Lab 8: Metamorphic Rocks and Processes
Name: Date:
7.
Quartz sandstone is a sedimentary rock and is the parent rock
(protholith) of quartzite, a metamorphic rock. i.
With your lab group, observe and discuss the changes that took
place when the sandstone underwent metamorphism into
quartzite. Texture changed (coarser) and no creation of foliations. Grains
are slightly bigger.
ii.
Additionally, hypothesize what caused these changes to occur.
Sandstone does not have tabular minerals. High temperature is
certainly a factor. High pressure seems unlikely due to lack of
platy minerals and no change in composition. Contact
metamorphism!
8.
Compare and contrast how this activity relates to what you observed in Part A?
Shale, having tabular minerals, resulted in a flat rock after an increase in temperature and pressure. This means the minerals expanded with the same orientation. Sandstone, having more round, blunt minerals, did not create foliations.
9.
Gneiss can form through the metamorphosis of granite, but can also form at the highest grade of metamorphism in the shale series pictured above. 4
toliths
. Please click on images to
see more detail/zoom in.
granite
gneiss
GEOL 101L Lab 8: Metamorphic Rocks and Processes
Name: Date:
a.
Which statement below best describes metamorphic changes from granite
gneiss? (select one)
i.
The mineral composition of gneiss appears significantly different from granite
ii.
The texture of gneiss appears significantly different from granite
b. Which statement below best describes metamorphic changes from shale
slate
phyllite
schist
gneiss? (select one)
i.
The mineral composition of gneiss appears significantly different from shale
ii.
The texture of gneiss appears significantly different from shale
**use color as proxy for composition
10.
Marble forms through the metamorphosis of limestone. Which statement below best describes metamorphic changes from limestone
marble? (select one)
i.
The mineral composition of marble appears significantly different from limestone
ii.
The texture of marble appears significantly different from limestone
**know both limestone and marble react with acid
**tells us mineralogy is relatively same
Part C: Classification and Identification of Metamorphic Rocks
You will use the observation of texture and composition of common metamorphic rocks to determine their name, probable parent rock and metamorphic conditions. Please go to: https://meg.georockme.com/unknowns
to view the samples.
5
limestone
marble
GEOL 101L Lab 8: Metamorphic Rocks and Processes
Name: Date:
11.
With your lab group, observe each metamorphic rock’s texture and composition to determine its type and parent rock.
Slate, phyllite, schist, gneiss, quartzite
Sample #
Foliation (Y/N)
Grain Size and
other identifying
characteristics
(Coarse/Fine)
Dominant Mineral
(quartz, calcite, mica,
N/A)
Rock Name
Parent
Rock (Protolith)
A01
N
Coarse
Quartz
Quartzite
Quartz sandstone
A02
Y
Fine
N/A
Slate
Shale
A03
Y
Coarse
N/A
Gneiss
Shale/granite
A04
N
Coarse
Calcite
M
arble
Limestone
A06
Y
Coarse
Mica
Schist
Shale
A07
Y
Fine
Mica
P
hyllite
Shale
Metamorphic Rocks Identification Flowchart
(left side) and Protoliths
(right side)
6
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