cee 437 lecture 4 igneous and metamorphic rocks, rock lab
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Northwest Igneous and Metamorphic Rocks
Columbia River Basalts
(miocene)
Snake River Basalts
(pliocene)
Yellowstone Region Acidic Volcanics (Pleistocene to
recent)
Cascade Volcanoes (recent)
Recent Basaltic Volcanism (Newberry Crater)
Cascade Batholiths (Felsic, Cret-Miocene)
Geologic Settings for Igneous Rocks
• Oceanic– Hi Fe, Mg, Ca, low Si– basalt, gabbro
• Continental – Hi Si, Na, K– granite, rhyolite, andesite
Igneous Origins
• Intrusive– Batholithic or plutonic: phaneritic– Dikes or sills that chill rapidly: aphanitic
• Extrusive– deposition as melt (lava)– pyroclastic
• tuff• tephra• pyroclastic flows
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
Igneous Rock Classification
SERPENTINITE
Acidic, Felsic Basic, Mafic Ultramafic
Common Types in RED outline
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
Structures of Basalt Flows
• Lava Tubes• Flow Stratigraphy
– collonade– entablature– flow top breccia/scoria
Metamorphic Classification
• Original Material– sandstone, limestone, shale, basalt)
• Metamorphic Grade (Temperature, Pressure)
• Source of Metamorphism (Regional, Contact)
Basic Metamorphic Types
• Quartz Sandstone Quartzite• Limestone, Dolomite Marble• Shale
– Slate — cleavage, no visible xl’s– Phyllite — foliation, mica sheen but xl’s not visible– Schist — clear foliation, visible mica– Gneiss — like granite but with foliation/gneissosity
• Basalt greenschist, amphibolite
Northwest Igneous and Metamorphic Rocks
Columbia River Basalts
(miocene)
Snake River Basalts
(pliocene)
Yellowstone Region Acidic Volcanics (Pleistocene to
recent)
Cascade Volcanoes (recent)
Recent Basaltic Volcanism (Newberry Crater)
Cascade Batholiths (Felsic, Cret-Miocene)
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