sedimentary and metamorphic rocks
DESCRIPTION
Sedimentary and Metamorphic Rocks. Sedimentary Rocks. Made from sediment / organic matter Rock goes through weathering and erosion, and is broken down into tiny fragments, some of which may be chemically altered Sediment Sediment is compacted and cemented - PowerPoint PPT PresentationTRANSCRIPT
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Sedimentary and Metamorphic Rocks
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Made from sediment / organic matter Rock goes through weathering and erosion, and is
broken down into tiny fragments, some of which may be chemically altered Sediment
Sediment is compacted and cemented Squeezed together; dissolved minerals crystallize and act as
“cement” to bond sediment together COMPACTION AND LITHIFICATION
Sedimentary Rocks
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How do sedimentary rocks form? Clastic
Sediment is compacted and cemented Further classified by size of sediment grain Sediment is held together by matrix material (“cement”)
Chemical; biogenic Dissolved substances precipitate out of solution leaving a solid
product OR Made from organic matter May CONTAIN FOSSILS! Tells about previous conditions on earth!
Classifying Sedimentary Rocks
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Sandstone – beaches, desert Ripples, sand dune patterns in layers to determine which environment
Shale; mudstone – deep, calm water Water must be deep, calm enough for fine sediment grains to deposit Lake and ocean bottoms
Limestone – deepest water, coral reefs Shelled organisms die, CaCO3 accumulates
Conglomerate – rivers; glaciers Rivers transports differently-sized particles that deposit along shore,
riverbed, etc.; cemented together with mud to form stone Rivers can transport materials long distances
Coal – swamp Halite – dried up body of salt water
Depositional Environment
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C. Chesterman, 1979
Sedimentary rock samples (left; and sedimentary rocks in outcrop. Note the layers, or strata, that you can see in the sedimentary rock.
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Previous existing rocks that go through extreme T and P changes that chemically alters the rock (ROCK DOES NOT MELT)
Contact metamorphism -- comes into contact with magma (small scale)
Regional metamorphism -- large, extreme changes and deformation
Metamorphic Rocks
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Heat Magma Change in location (depth) of rock
E.g. - Cookies! Minerals become unstable and recrystallize
Heat is energy source that drives change Pressure
Causes mineral grains to compact Can create a new density or cause minerals to recrystallize
Hydrothermal solution Hot water / mineral solutions that dissolve some substances in
mineral, deposit new ones, causes change in composition
Agents of Metamorphism
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Degree of foliation Minerals recrystallize, can be re-oriented Appears layered / banded Due to preferred orientation of mineral (stress and strain!)
How Metamorphic Rocks are Classified
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Nonfoliated Not banded Usually only one mineral in rock composition
Classification cont’d
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Rock type: type of metamorphism Volcanism, mountain building
Parent rock type -- history Shale / siltstone - slate -> schist -> gneiss with T or P
Sometimes just burial Granite, Schist -> Gneiss……with intense T or P
Mountain building Can determine direction of force from foliation More T and P -> Melting of Gneiss….back to Granite!
Limestone -> marble Sandstone -> quartzite Organic coal -> anthracite coal (just burial…increased P, Low T)
Metamorphism, Environment, and History
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Formation of Coal
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C. Chesterman, 1979
Here are a few examples of metamorphic rocks (samples to the right, rock outcrop above).