Post on 30-Dec-2015
description
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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…
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There’s a mineral
There’s a mineral
There’s a mineral
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A metamorphic rock is a reprocessed
igneous or sedimentary rock…
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In other words, it has been recycled…
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A metamorphic rock is a barometer, an
indicator of changes in pressure and
temperature …(PT)
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When a metamorphic rock
undergoes changes in PT, the texture of
the rock changes
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The word metamorphic means change in
shape…
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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…
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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…
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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…
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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…
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THE END…ask Bob for
a worksheet!