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CEE 437 Rocks!

CEE 437 Rocks!. Thomas Doe. Silica Tetrahedron. Feldspar Structure. All tetrahedra corners occupied Both Si and Al tetrahedra Cations in voids of structure to balance charge. Feldspar Compositions. Clay Minerals. Extremely Important Mineral Group Seals Stability Pore pressure

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CEE 437 Rocks!

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  1. CEE 437 Rocks! Thomas Doe

  2. Silica Tetrahedron

  3. Feldspar Structure • All tetrahedra corners occupied • Both Si and Al tetrahedra • Cations in voids of structure to balance charge

  4. Feldspar Compositions

  5. Clay Minerals • Extremely Important Mineral Group • Seals • Stability • Pore pressure • Chemical interaction • Swelling • Slaking • Confusion as both “Size” and “Mineral” Classification

  6. Clay Sources • Weathering • Hydrothermal Alteration • Deposition • Clay Transformations • Feldspar  Illite, Kaolinite • Ferro-Magnesian  Chlorite • Volcanics (alkaline conditions)  Smectite • Volcanics (acidic conditions)  Kaolinite • Bentonite: plastic, highly swelling

  7. Clay Units From West, Geology Applied to Engineering, Prentice Hall, 1995)

  8. Two and Three-Layer Clay Structure From West, Geology Applied to Engineering, Prentice Hall, 1995)

  9. Mixed Layer Clays From West, Geology Applied to Engineering, Prentice Hall, 1995)

  10. Clay Viewed from Electron Microscope

  11. 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)

  12. Geologic Settings for Igneous Rocks • Oceanic • Hi Fe, Mg, Ca, low Si • basalt, gabbro • Continental • Hi Si, Na, K • granite, rhyolite, andesite

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

  14. 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

  15. Igneous Rock Classification Acidic, Felsic Basic, Mafic Ultramafic SERPENTINITE

  16. Magma Generation on Continental Margins

  17. Magma Generation in Convergent Continental Plate Margins

  18. 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

  19. Volcano Types Basaltic: low viscosity — Hawaii, Columbia Plateau Andesitic/Rhyolitic

  20. Structures of Basalt Flows • Lava Tubes • Flow Stratigraphy • collonade • entablature • flow top breccia/scoria

  21. Hawaii Basalt Flows

  22. Basalt Flow Structures

  23. Eruptions of Acid-Rock Volcanoes

  24. Rhyolite Dome

  25. Caldera

  26. Mt. St. Helen’s Blast Zone

  27. Mt. Mazama Ash Distribution

  28. 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

  29. Non-foliated Metamorphic Rocks • Sandstone —> Quartzite • Limestone —> Marble • Dolomite —> Dolomitic Marble

  30. Foliated Metamorphic Rocks • Shale/Mudstone • Slate • Phyllite (Greek for leaves e.g. phyllo dough) • Schist • Gneiss

  31. Origin of Foliation (gneissosity, schistosity)

  32. Engineering Properties • Anisotropy of strength and elastic properties • Preferred failure on foliation

  33. Slate

  34. Phyllite

  35. Schist

  36. Chlorite Schist

  37. Gneiss

  38. Banded Gneiss

  39. Metamorphic Grade

  40. Subduction-Zone Metamorphism

  41. Metamorphism at Continental Collisions

  42. Contact Metamorphism

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

  44. Rock Cycle Crystallization at depth or extrusion at surface Magma Melting Igneous Rocks Burial, metamorphism, recrystallization Metamorphic Rocks Weathering, Erosion Sediments Burial, metamorphism, recrystallization Sedimentary Rocks Lithification

  45. Sediment Sources

  46. Clastic Sedimentary Rocks • 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)

  47. Clastic Sedimentary Rocks • Clay, muds  shales, mudstones, claystones (difference based on fissility) • Silts  siltstones • Sands  sandstones • Gravels  Conglomerates (Breccia if angular, breccia may also be a term for tectonically fragmented rock)

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