CEE 437 Lecture 2 Earth Materials I Earth

CEE 437 Lecture 2 Earth Materials I Earth Structure and Minerals Thomas Doe

Outline Global tectonic setting n Rock cycle n Rock forming minerals n Paper 1 n

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

Velocity Variation with Depth

Global Structure

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

Global Seismicity

Benioff Zone

Seafloor Spreading — Sediment Ages

Sea-floor Spreading n Mantle convection driven

Evolution of Spreading Sea Floor — Atlantic Analog

Convergent Margins Ocean to Continent n Continent to Continent n

Convergent Margin - Continental

Subduction Zone – Island Arc

Evolution of Continents — North American Craton

North American Accretion

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

Mineral Differentiation n Plate tectonics and Igneous Processes n n n Weathering and Erosion n n selective melting, selective recrystallization differentiation by density Selective weathering Concentration of quartz (pure Si 02) Conversion of alumino-silicates to clays Concentration of soluble residues in seawater Deposition n Courser materials near sediment source Finer materials far from sediment source Redeposition of salts and solutes by evaporative (Na, KCl; Ca. SO 4) or biological processes (Ca. CO 3, ; )

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

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

Bowen’s Reaction Series

Crustal Composition n Main Elemental Groups n n Silica Aluminum Ferro-Magnesian Ca, Na, K

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

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

Sedimentary Differentiation Sorting by Deposition Medium n Sorting by Energy n

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

Galena, Pb. S Graphite, C

Crystalline Structure of Calcite

Crystalline Symmetry Groups

Isomorphic Crystal Forms, Cubic System

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

Properties and Mineral Symmetry

Tensor Properties of Crystals Cubic Group Lower Symmetry Groups General Form for Heat Flow (for example)

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

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

Crustal Composition n Main Elemental Groups n n Silica Aluminum Ferro-Magnesian Ca, Na, K

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

Silica Tetrahedron

Forms of Silicates

Deformation Mechanisms

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

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

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

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

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

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

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

Topics Mineral Definition n Rock Forming Minerals n Physical Proprieties of Minerals n Mineral Identification n Mineral Lab n

Clay Viewed from Electron Microscope

Mineral Identification Density n Hardness n Color, luster (metallic, non-metalic, semimetallic) n Crystalline habit n Cleavage n Optical microscopy n Mineral chemistry, x-ray diffraction n

Hardness Scale

X-Ray Diffraction Bragg’s Law

Weathering Fates Feldspars to clays (clays, shales) n Quartz endures (siltstones, sandstones) n Calcium recirculated into carbonate minerals by organic processes (limestones) n n Consequence: n Over time, evolution of less dense more silicic continental crust

Engineering Implications n “Style” of geology and geo-engineering problems varies with plate tectonic setting n n Maturity of materials varies with plate tectonics setting n n Faulting, and structural complexity Higher degree of more stable materials from sorting by weathering Geohazards vary with plate tectonic setting

Paper and Paper Topics Paper I Topics n Columbia River Basalts – Origin, Structure, Hydrologic and Engineering Properties n Geology and Engineering Geology of the Snoqualmie Pass Quadrangle n Clay Minerals – Origin, Crystal Structure, Engineering Properties n 6 Pages, 1. 5 space, plus figures, include references. n

Undergrad Presentations n n n n 1. Geologic History of Columbia Plateau 2. Geologic History of Olympic Peninsula 3. Coal Mines of Newcastle, Washington 4. Geological Issue Effecting Construction I-5 through Seattle 5. The Seattle Fault 6. Foundations on Peat 7. Rock Slope Stability Problems in I-90 8. Fracture Image Logging Technologies 9. Tunneling for Sound Transit 10. Engineering Properties of Organic Soils in the Puget Sound Area 11. Engineering Properties of Glacial Soils in the Puget Sound Area 12. Solute Transport in Fractured Rock 13. Economic Minerals of Washington State 14. Quarry Mines of Puget Sound 15. Failure of Malpassat Dam 16. Rock Tunnel Failures in the Alps 17. Seattle Watershed Geology

Grad Requirements n Add Goodman – Engineer as Artist (unless discuss with us otherwise)

Paper and Paper Topics Paper I Topics n Columbia River Basalts – Origin, Structure, Hydrologic and Engineering Properties n Geology and Engineering Geology of the Snoqualmie Pass Quadrangle n Clay Minerals – Origin, Crystal Structure, Engineering Properties n 6 Pages, 1. 5 space, plus figures, include references. n