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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!