CEE 437 Lecture 2 Earth Materials I Earth Structure and Minerals

1. CEE 437 Lecture 2Earth Materials IEarth Structure and Minerals Thomas Doe

2. Outline • Global tectonic setting • Rock cycle • Rock forming minerals • Paper 1

3. Announcements • Paper and Quiz Schedule • Quiz 1 10-11 • Paper 1 10-18 • Field Trips • Oct 23 • Nov 20 • Office and Hours • 132 G More • Before class (3:00) or by appointment

4. Global Structure • Based mainly on seismic information and meteorite compositions • Crust ~25-75 km depending varying under continents and oceans

5. Velocity Variation with Depth

6. Global Structure

7. Development of Plate Tectonics • Evidence from ocean floor magnetism and ages • Evidence from seismicity • Evidence from cross-continent correlations of rocks

8. Global Seismicity

9. Benioff Zone

10. Seafloor Spreading — Sediment Ages

12. Sea-floor Spreading • Mantle convection driven

13. Evolution of Spreading Sea Floor — Atlantic Analog

15. Convergent Margins • Ocean to Continent • Continent to Continent

16. Convergent Margin - Continental

17. Subduction Zone – Island Arc

18. Evolution of Continents — North American Craton

19. North American Accretion

20. 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

21. Mineral Differentiation • Plate tectonics and Igneous Processes • selective melting, selective recrystallization • differentiation by density • Weathering and Erosion • Selective weathering • Concentration of quartz (pure Si02) • Conversion of alumino-silicates to clays • Concentration of soluble residues in seawater • Deposition • Courser materials near sediment source • Finer materials far from sediment source • Redeposition of salts and solutes by evaporative (Na,KCl; CaSO4) or biological processes (CaCO3,; )

22. Differentiation of Crustal Composition Weathering differentiating towards higher Silica Carbonate concentrated by organic processes Preferential melting of high-silica materials Original basaltic composition of crust Concentration of C, Ca, Na, K in sea and air

23. Bowen Reaction Series • How to get many different rocks from one melt composition? • Differentiation by selective crystallization and removal from system

24. Bowen’s Reaction Series

25. Crustal Composition • Main Elemental Groups • Silica • Aluminum • Ferro-Magnesian • Ca, Na, K

26. Elemental Fates • Silicon tends to concentrate in crust — quartz is very long lived • Aluminum — transforms from feldspars to clays • Mica — transform to clays • Fe-Mg-Ca-Na-K concentrate in some clays and micas, concentrate in oceans in biosphere

27. Differentiation in Crystallization Versus Differentiation in Weathering Slow Weathering Quartz Low Temperature, High Silica, Low Fe Mg Muscovite K-Feldspars Biotite Amphibole Ca,Mg Feldspars High Temperature, Low Silica, Hi Fe Mg Pyroxene Fast Weathering Olivine

28. Sedimentary Differentiation • Sorting by Deposition Medium • Sorting by Energy

29. Mineral Definition • Naturally occurring material with unique combination of chemical composition and crystalline structure • Natural non-minerals — glasses, coal, amorphous silica • Pseudomorphs: diamond:graphite

30. Graphite, C Galena, PbS

31. Crystalline Structure of Calcite

32. Crystalline Symmetry Groups

33. Isomorphic Crystal Forms, Cubic System

34. Physical Properties • Density (Gravity) • Electrical Conductivity (Resisitivity) • Thermal Expansion • Strength • Elasticity (Mechanical properties, • Seismic/Acoustic Velocity • Rheology (Plasticity,Viscosity)

35. Discussion: How to Rock Properties Relate to Mineral Structure • How will anisotropy vary with crystal symmetry class? • Rock Salt versus Quartz? • How will aggregates of minerals (with same mineral behave? • Cubic versus non cubic • Rock fabric • Material property contrasts

36. Rock Forming Minerals • Composition of Crust • Dominantly O, Si, Fe, Mg, Ca, Na, K • Near surface importance of bio-processes • Silicates from inorganic processes • Carbonates mainly from shell-forming organisms

37. Crustal Composition • Main Elemental Groups • Silica • Aluminum • Ferro-Magnesian • Ca, Na, K

38. Major Silicate Groups • Silicon Tetrahedron • separate tetrahedra — olivine • single chains — pyroxene • double chains — amphibole • sheet silicates — micas and clays • framework silicates — feldspars (with Al substitution), quartz as pure silica

39. Silica Tetrahedron

41. Forms of Silicates

42. Deformation Mechanisms

43. Effects on Physical Properties • Anisotropy • Properties differ by direction • Heterogeneity • Properties vary by location • Mineral properties may have strong anisotropy when crystals are aligned • Heterogeneity may have strong mechanical effects when different minerals have different deformation properties

44. Minerals Elements Anisotropy from crystal structure Elastic Properties Thermal Properties Optical Properties Deformation Shear transformations Dislocations Rock Elements Intragranular Anisotropy from fabric Crystal anisotropy if preferred orientation Anisotropy from bedding, foliation, flow structures Intergranular Cements Microcracks Heterogeneity Mineral composition Other segregration processes Minerals versus Rocks

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

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

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

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

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