Northwest igneous and metamorphic rocks

CEE 437
Rocks!
Thomas Doe


Outline
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Igneous Rocks
Sedimentary Rocks
Metamorphic Rocks
Rock Identification Lab


Rock Cycle
Crystallization at depth or
extrusion at surface

Igneous Rocks

Sediments

Lithification

Magma
Burial, metamorphism,
recrystallization

Weathering,
Erosion

Melting

Metamorphic
Rocks
Burial,
metamorphism,
recrystallization

Sedimentary Rocks


Northwest Igneous and
Metamorphic Rocks
Cascade Volcanoes
(recent)
Cascade Batholiths
(Felsic, CretMiocene)

Columbia River
Basalts
(miocene)

Recent
Basaltic
Volcanism
(Newberry
Crater)

Snake River
Basalts
(pliocene)

Yellowstone Region
Acidic Volcanics
(Pleistocene to
recent)


Geologic Settings for Igneous
Rocks
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Oceanic
 Hi Fe, Mg, Ca, low Si
 basalt, gabbro

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Continental
 Hi Si, Na, K
 granite, rhyolite, andesite


Igneous Origins
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Intrusive
 Batholithic or plutonic: phaneritic

 Dikes or sills that chill rapidly: aphanitic

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Extrusive
 deposition as melt (lava)
 pyroclastic

tuff
 tephra
 pyroclastic flows
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Identifying Igneous Rocks
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Chemistry
 Acidic: Basic (more Si, less Si)

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Texture
 Aphanitic: crystals not visible
 Phaneritic: made of visible crystal components
 Porphyritic: Larger crustals in aphanitic or phaneritic ground mass


Igneous Rock Classification
Acidic, Felsic

Basic, Mafic

Ultramafic

SERPENTINITE



Magma Generation on Continental
Margins


Magma Generation in Convergent
Continental Plate Margins


Extrusives
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Viscosity varies with Si and water content
 Basalt — low viscosity
 Rhyolite — high viscosity

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Rhyolite flows relatively unusual as rhyolite does
not flow well
 Explosive
 Tuffs, pyroclastics

Volcano Types

Basaltic: low
viscosity — Hawaii,
Columbia Plateau

Andesitic/Rhyolitic


Structures of Basalt Flows
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Lava Tubes
Flow Stratigraphy
 collonade
 entablature
 flow top breccia/scoria


Hawaii Basalt Flows


Basalt Flow Structures


Eruptions of Acid-Rock Volcanoes

Rhyolite Dome


Caldera


Mt. St. Helen’s Blast Zone


Mt. Mazama Ash Distribution


Sedimentary Rocks
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Clastics, Siliciclastics, and Evaporites
Clastic rocks, depositional medium, and energy
Diagenesis — chemical changes after deposition


Rock Cycle
Crystallization at depth or
extrusion at surface

Igneous Rocks

Sediments

Lithification

Magma
Burial, metamorphism,
recrystallization

Weathering,
Erosion

Melting

Metamorphic
Rocks
Burial,
metamorphism,
recrystallization

Sedimentary Rocks


Sediment Sources


Clastic Sedimentary Rocks
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Clastic — broken like iconoclast)
Often referred to as Siliciclastics as having Si
based rock forming minerals
Based on grain size and to a lesser extent
composition
Grain size related to energy of depositional
environment
 Relationship of medium velocity to maximum grain size)