مواضيع المحاضرة: جيولوجيا
قراءة
عرض

CEE 437 Lecture 2 Earth Materials I Earth Structure and Minerals

مكونات الارض

Outline

Global tectonic setting
Rock cycle
Rock forming minerals
Paper 1

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

Global Structure

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

Velocity Variation with Depth

Global Structure

Development of Plate Tectonics

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

Global Seismicity

Benioff Zone

Seafloor Spreading — Sediment Ages

Sea-floor Spreading
Mantle convection driven

Evolution of Spreading Sea Floor — Atlantic Analog

Convergent Margins
Ocean to Continent
Continent to Continent

Convergent Margin - Continental

Subduction Zone – Island Arc

Evolution of Continents — North American Craton

North American Accretion

Rock Cycle

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

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,; )

Differentiation of Crustal Composition

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

Bowen Reaction Series

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

Bowen’s Reaction Series

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

Elemental Fates

Silicon tends to concentrate in crust — quartz is very long livedAluminum — transforms from feldspars to claysMica — transform to clays Fe-Mg-Ca-Na-K concentrate in some clays and micas, concentrate in oceans in biosphere

Differentiation in Crystallization Versus Differentiation in Weathering

Olivine
Pyroxene
Amphibole
Biotite
Muscovite
Quartz
Ca,Mg Feldspars
K-Feldspars
High Temperature, Low Silica, Hi Fe Mg
Low Temperature,
High Silica, Low Fe Mg
Fast Weathering
Slow Weathering

Sedimentary Differentiation

Sorting by Deposition Medium
Sorting by Energy

Mineral Definition

Naturally occurring material with unique combination of chemical composition and crystalline structureNatural non-minerals — glasses, coal, amorphous silicaPseudomorphs: diamond:graphite

Galena, PbS

Graphite, C

Crystalline Structure of Calcite

Crystalline Symmetry Groups

Isomorphic Crystal Forms, Cubic System

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

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

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

Crustal Composition

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

Major Silicate Groups

Silicon Tetrahedronseparate tetrahedra — olivinesingle chains — pyroxenedouble chains — amphibolesheet silicates — micas and claysframework silicates — feldspars (with Al substitution), quartz as pure silica

Silica Tetrahedron

Forms of Silicates

Deformation Mechanisms

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

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

Clay Minerals

Extremely Important Mineral GroupSealsStabilityPore pressureChemical interactionSwellingSlakingConfusion as both “Size” and “Mineral” Classification

Clay Sources

WeatheringHydrothermal AlterationDepositionClay TransformationsFeldspar  IlliteFerro-Magnesian  ChloriteVolcanics (alkaline conditions)  SmectiteVolcanics (acidic conditions)  KaoliniteBentonite: 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
Rock Forming Minerals
Physical Proprieties of Minerals
Mineral Identification
Mineral Lab

Clay Viewed from Electron Microscope

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

Hardness Scale

X-Ray Diffraction
Bragg’s Law

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

Engineering Implications

“Style” of geology and geo-engineering problems varies with plate tectonic settingFaulting, and structural complexityMaturity of materials varies with plate tectonics settingHigher degree of more stable materials from sorting by weatheringGeohazards vary with plate tectonic setting

Paper, 10-18

1. Physical Properties of Rocks and CrystalsPrepare 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 deformabilityRole 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 SilicatesDefine clay versus micaPhysical properties of claysDifferentiation of clays types“Bad Actors”3. The Rock Cycle and Its Influence on Rock Material Properties (non-geologists)Differentiation by Plate Tectonics, Weathering and DepositionTrack clays through the Rock Cycle4. Other topic (pre-approval recommended)



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