1 Lab 07 ONLINE LESSON Use down or up arrows to navigate
1 Lab 07 ONLINE LESSON Use down or up arrows to navigate.
Dec 16, 2015
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1
Lab 07 ONLINE
LESSON
Use down or up arrows to navigate
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DO TAKE NOTES WHILE PERUSING
ALONG…
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Metamorphic Rocks
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As we saw last time, a rock is a
collection of minerals…
5
There’s a mineral
There’s a mineral
There’s a mineral
6
A metamorphic rock is a reprocessed
igneous or sedimentary rock…
7
In other words, it has been recycled…
8
A metamorphic rock is a barometer, an
indicator of changes in pressure and
temperature …(PT)
9
When a metamorphic rock
undergoes changes in PT, the texture of
the rock changes
10
The word metamorphic means change in
shape…
11
Here is a parent rock called granite…
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Pressures and temperatures will
increase…
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And this rock will transform into…
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A metamorphic rock…
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A metamorphic rock…
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Wow. Did you see that. Do you want to see it
again?
Go forward…
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A metamorphic rock…
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Pretty slick eh!
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Slick as snot!
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The original rock called granite was heated up
and pressurized such that the texture of the rock
changed…
21
The rock started out as an igneous rock then ended
up as a transformed metamorphic rock called
gneiss…
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The Rock Cycle tells us that rocks first start out as igneous rocks…
23
Eventually, these rocks undergo changes…
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Weathering is the process of breaking up rocks…big rocks turn into small rocks
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Sediment (small rocks) is transported and deposited where it forms into sedimentary rock…
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Igneous or sedimentary rocks undergo changes in PT…
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To become metamorphic rocks…
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Some metamorphic rocks encounter so much change that they go back to an igneous state…hence the rock cycle…
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For example…
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Limestone (1) is deposited…
(1)
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Limestone is covered by more sediment (x)…
(x)
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Pressures increase until the minerals in the limestone are altered…
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Producing marble (2)…
(2)
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Another example…
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Sandstone (3) is deposited…
(3)
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Pressures increase until the minerals in the sandstone are altered…
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Producing quartzite (4)…
(4)
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Metamorphic rocks are indicators of
changes in pressure and temperature
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They tell us which environments rocks
have gone through…
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Another, another example…
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Shale undergoes a series of metamorphic transformations…
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Shale (5) is transformed into slate (6)…
(5)(6)
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Then onto phyllite (7)…and schist (8) then gneiss (9)
(5)(6) (7)
(8)(9)
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No more rock after gneiss…total melting occurs after that…
45
So shales (mudstones)
undergo a series of transformations…
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This is called progressive
metamorphism…a parent rock starts
out as shale…
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Then goes through a series of
transformations until the end product of
gneiss…
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Shale is low temperature…
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Schist a bit higher PT…and so on…
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Gneiss is at the highest PT before melting…
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Each of the intermediate steps gives geologists
clues to the PT environment…
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In which shale went through on its
metamorphic journey to gneiss…
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WOW
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When discussing metamorphic rocks …
plates tectonics has to be mentioned…
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Igneous and sedimentary rocks will appear at the
surface but are then heated and pressurized
courtesy of plate tectonics…
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Here, we see tectonics in actionThe lithosphere is subductingPlutons are formingRising up through continental crustProducing metamorphic rocks…Right click on animation to start flash movie
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As bubbles of liquid rock (plutons) rise up…the surrounding cool rock becomes baked and
metamophosed…
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This is contact metamorphism…
involving lots of heat…
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Pluton
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As rocks collide into each other, PT increases
forming metamorphic rocks…
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Colliding plates produce heat and pressure producing metamorphic rocks…
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Some features of metamorphic rocks…
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Geologists will say that the minerals in
metamorphic rocks equilibrate with their
surroundings…
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In other words, they adjust to their surroundings…if
the temperature goes up…minerals will melt…
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And change to a more stable mineral…
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Different minerals will melt at varying temperatures…
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Minerals will change at different pressures…
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Ice melts at room temperature
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Cheese melts at 55 °C
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Quartz melts at about 1670 °C
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Pyrite melts at about 1177 °C
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So when minerals melt within a metamorphic
rock, the overall texture will change…
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Textures of metamorphic rocks…
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A shale (parent rock) contains lots of mica like
minerals…
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When pressure is applied, the minerals will be
realigned…
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This action changes the texture of a rock…
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Producing a smoother texture…
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Shales (includes mudstones) start out as
dull rocks…
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After metamorphic actions, the shale is
transformed into a schist with a different appearance…
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Here is a schist…
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Notice how shiny it is…
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Minerals have been realigned
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Notice the transformation…
Before After
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So metamorphic rocks are barometers of changes in
pressure and temperature…
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PT will increase with depth… metamorphic actions occur… changing rocks from one type to another…
86
THE END…ask Bob for
a worksheet!
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