CEE%20437%20Lecture%204%20Igneous%20and%20Metamorphic%20Rocks,%20Rock%20Lab

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CEE 437 Lecture 4Igneous and Metamorphic Rocks,
Rock Lab

• October 10, 2002
• Thomas Doe

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Outline

• Igneous Rocks
• Metamorphic Rocks
• Rock Identification Lab

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Northwest Igneous and Metamorphic Rocks
Cascade Volcanoes (recent)
Cascade Batholiths (Felsic, Cret-Miocene)
Columbia River Basalts (miocene)
Recent Basaltic Volcanism (Newberry Crater)
Yellowstone Region Acidic Volcanics (Pleistocene
to recent)
Snake River Basalts (pliocene)
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Geologic Settings for Igneous Rocks

• Oceanic
• Hi Fe, Mg, Ca, low Si
• basalt, gabbro
• Continental
• Hi Si, Na, K
• granite, rhyolite, andesite

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Igneous Origins

• Intrusive
• Batholithic or plutonic phaneritic
• Dikes or sills that chill rapidly aphanitic
• Extrusive
• deposition as melt (lava)
• pyroclastic
• tuff
• tephra
• pyroclastic flows

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Identifying Igneous Rocks

• Chemistry
• Acidic Basic (more Si, less Si)
• Texture
• Aphanitic crystals not visible
• Phaneritic made of visible crystal components
• Porphyritic Larger crustals in aphanitic or
  phaneritic ground mass

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Igneous Rock Identification
Igneous Rock Identification
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Igneous Rock Classification
Acidic, Felsic
Basic, Mafic
Ultramafic
SERPENTINITE
Common Types in RED outline
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Igneous Structural Features
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Magma Generation on Continental Margins
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Magma Generation in Convergent Continental Plate
Margins
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Igneous Structures
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Extrusives

• Viscosity varies with Si and water content
• Basalt low viscosity
• Rhyolite high viscosity
• Rhyolite flows relatively unusual as rhyolite
  does not flow well
• Explosive
• Tuffs, pyroclastics

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Volcano Types
Basaltic low viscosity Hawaii, Columbia
Plateau
Andesitic/Rhyolitic
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Structures of Basalt Flows

• Lava Tubes
• Flow Stratigraphy
• collonade
• entablature
• flow top breccia/scoria

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Hawaii Basalt Flows
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Basalt Flow Structures
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Eruptions of Acid-Rock Volcanoes
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Rhyolite Dome
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Caldera
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Mt. St. Helens Blast Zone
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Mt. Mazama Ash Distribution
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Subduction-Zone Metamorphism
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Metamorphism

• Recrystallization of Rock Under Temperature and
  Pressure

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Metamorphic Rock Classification
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Metamorphic Classification

• Original Material
• sandstone, limestone, shale, basalt)
• Metamorphic Grade (Temperature, Pressure)
• Source of Metamorphism (Regional, Contact)

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Basic Metamorphic Types

• Quartz Sandstone ? Quartzite
• Limestone, Dolomite ? Marble
• Shale ?
• Slate cleavage, no visible xls
• Phyllite foliation, mica sheen but xls not
  visible
• Schist clear foliation, visible mica
• Gneiss like granite but with foliation/gneissosi
  ty
• Basalt ? greenschist, amphibolite

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Origin of Foliation (gneissosity, schistosity)
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Metamorphism at Continental Collisions
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Contact Metamorphism
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Metmorphic Grade
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Northwest Igneous and Metamorphic Rocks
Cascade Volcanoes (recent)
Cascade Batholiths (Felsic, Cret-Miocene)
Columbia River Basalts (miocene)
Recent Basaltic Volcanism (Newberry Crater)
Yellowstone Region Acidic Volcanics (Pleistocene
to recent)
Snake River Basalts (pliocene)
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Sauk River Quadrangle
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Malpasset Dam