CEE 437 Lecture 2 Earth Materials I Earth Structure and Minerals

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CEE 437 Lecture 2Earth Materials IEarth
Structure and Minerals

• Thomas Doe

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Outline

• Global tectonic setting
• Rock cycle
• Rock forming minerals
• Paper 1

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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 (300) or by appointment

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Global Structure

• Based mainly on seismic information and meteorite
  compositions
• Crust 25-75 km depending varying under
  continents and oceans

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Velocity Variation with Depth
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Global Structure
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Development of Plate Tectonics

• Evidence from ocean floor magnetism and ages
• Evidence from seismicity
• Evidence from cross-continent correlations of
  rocks

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Global Seismicity
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Benioff Zone
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Seafloor Spreading Sediment Ages
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Sea-floor Spreading

• Mantle convection driven

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Evolution of Spreading Sea Floor Atlantic Analog
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Convergent Margins

• Ocean to Continent
• Continent to Continent

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Convergent Margin - Continental
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Subduction Zone Island Arc
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Evolution of Continents North American Craton
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North American Accretion
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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
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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,
  )

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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
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Bowen Reaction Series

• How to get many different rocks from one melt
  composition?
• Differentiation by selective crystallization and
  removal from system

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Bowens Reaction Series
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Crustal Composition

• Main Elemental Groups
• Silica
• Aluminum
• Ferro-Magnesian
• Ca, Na, K

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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

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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
Olivine
Fast Weathering
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Sedimentary Differentiation

• Sorting by Deposition Medium
• Sorting by Energy

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Mineral Definition

• Naturally occurring material with unique
  combination of chemical composition and
  crystalline structure
• Natural non-minerals glasses, coal, amorphous
  silica
• Pseudomorphs diamondgraphite

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Graphite, C
Galena, PbS
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Crystalline Structure of Calcite
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Crystalline Symmetry Groups
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Isomorphic Crystal Forms, Cubic System
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Physical Properties

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

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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

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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

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Crustal Composition

• Main Elemental Groups
• Silica
• Aluminum
• Ferro-Magnesian
• Ca, Na, K

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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

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Silica Tetrahedron
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Forms of Silicates
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Deformation Mechanisms
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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

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Minerals versus Rocks

• 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

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Clay Minerals

• Extremely Important Mineral Group
• Seals
• Stability
• Pore pressure
• Chemical interaction
• Swelling
• Slaking
• Confusion as both Size and Mineral
  Classification

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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

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

• Mineral Definition
• Rock Forming Minerals
• Physical Proprieties of Minerals
• Mineral Identification
• Mineral Lab

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Clay Viewed from Electron Microscope
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Mineral Identification

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

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Hardness Scale
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X-Ray Diffraction
Braggs Law
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Weathering Fates

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

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Engineering Implications

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

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Paper, 10-18

• 1. Physical Properties of Rocks and Crystals
• Prepare a table of material properties for
  selected rock-forming minerals and corresponding
  rock types. You should use both library and web
  sources. Choose among the following concepts
• Role of mineral anisotropy and rock heterogeneity
  on strength and deformability
• Role of mineral anisotropy and rock heterogeneity
  on mechanical effects during rock heating and
  cooling (consider qualitatively the influence of
  differential responses)
• Useful Ref Carmichael, Handbook of Physical
  Properties of Rocks (CRC Press)
• 2. Structure and Properties of Sheet Silicates
• Define clay versus mica
• Physical properties of clays
• Differentiation of clays types
• Bad Actors
• 3. The Rock Cycle and Its Influence on Rock
  Material Properties (non-geologists)
• Differentiation by Plate Tectonics, Weathering
  and Deposition
• Track clays through the Rock Cycle
• 4. Other topic (pre-approval recommended)