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GEOS 251

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GEOS 251 Physical Geology 19 January 2012 Those wanting to add the class Come to the front of the room Reminder: Labs start next week, Gould-Simpson 201 – PowerPoint PPT presentation

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Title: GEOS 251


1
GEOS 251 Physical Geology
  • 19 January 2012
  • Those wanting to add the class
  • Come to the front of the room
  • Reminder Labs start next week, Gould-Simpson 201
  • Ground floor, north side of building
  • Introduction of TAs
  • All excellent geologists, very experienced TAs, ,
    committed to your success, and enthusiastic!
  • Working on D2L connection

2
Did you arrive with a particular career in mind?
  • Goodness, no. I not only didnt feel prepared, I
    had no idea what course of study I should follow.
    . . . You needed some language credits and some
    math credits some science. So your registration
    sheet filled up with required areas pretty fast.
  • I took a geology course and absolutely adored
    it, and I really thought, gosh, maybe thats what
    I should study. But I ended up majoring in
    economics.
  • --Who said this?

3
Did you arrive with a particular career in mind?
  • Goodness, no. I not only didnt feel prepared, I
    had no idea what course of study I should follow.
    . . . You needed some language credits and some
    math credits some science. So your registration
    sheet filled up with required areas pretty fast.
  • I took a geology course and absolutely adored
    it, and I really thought, gosh, maybe thats what
    I should study. But I ended up majoring in
    economics.
  • --Sandra Day OConnor, Stanford BA 50, JD 52
  • Interview in Stanford magazine, 2006

4
Teaching assistant for laboratory sessions and
field trips
  • Monday 1200-250pm (includes honors
    section)Ryan Leary
  • Tuesday 1230-315pmAdam Hudson
  • Wednesday 1200-250pmTyler Huth
  • Thursday 1230-315pmAdam Hudson

5
Society of Earth Sciences Students
http//www.geo.arizona.edu/SESS/
A club for all UA students interested in Earth
Science, regardless of major.
MEETINGS Every Friday at Noon Gould-Simpson Room
201 First Meeting January 20th Free pizza!
  • Activities
  • Field Trips
  • Guest Speakers
  • Social Events
  • Education Outreach

6
Question about tilt of Earths axis
  • Currently tilted 23.5 from the perpendicular to
    the ecliptic plane
  • Defined by orbital path around sun
  • Angle of tilt cycles between 21.5 and 24.5
  • Period of 41,000 y
  • Shape of the orbit also varies
  • This eccentricity has a period of 100,000 y
  • Axis also wobbles like a top
  • This precession has a period of 23,000 y
  • These three factors affect amount of solar
    radiationand climate (we will cover later, Ch.
    15)

7
Keys to doing well in this course
  • Attend the lectures
  • Reading the slides is a poor substitute for
    hearing the voice over and associated class
    discussion
  • My experience shows that the mean scores of
    students who attend lectures is at least one
    grade level above the mean of those who do not
    regularly attend lectures
  • Be present for all of the exams, and turn in all
    of the lab and field trip assignments
  • When you miss an activity, you earn a zero
  • This is far below the lowest failing grade for
    and assignment and thus is hard to compensate for
    later
  • I dont think anyone who attends lectures and
    turns in all assignments has ever received lass
    than a C in this class
  • Study and review the lecture summaries and do the
    reading

8
Last Time
  • Dynamic Earth
  • Physical and chemical differentiation of the
    Earth
  • Chemical layering according to density
  • Core, mantle, crust, fluid envelope
  • Physical layering according to strength
  • Lithosphere vs. asthenosphere
  • Thermal energy drives cycles
  • Dynamic geologic processes and time scales
  • Plate tectonic theory
  • Developed from geological observations and the
    hypothesis of continental drift
  • Basis for understanding and predicting many
    phenomena

9
Driving forces What are the energy sources for
the dynamic Earth?
  • Internal
  • Sources
  • Residual from Earths origin
  • Continual radioactive decay
  • Gravitational energy
  • Results
  • Move lithosphere, build mountains, make volcanoes
  • External
  • Source Solar energy
  • Results
  • Energizes atmosphere, oceans (climate, weather)

10
Why is the Earth dynamic?
  • Much of it behaves like a fluid (even many
    solids, given long enough time)
  • Light (less dense) material rises
  • Less dense because of composition
  • Less dense because of temperature (thermal
    convection)
  • Energy (heat) sources
  • Internal - plate tectonics
  • Solar - atmosphere and oceans

11
Plate Boundaries Three Types
  • Divergent (mid-ocean ridges - new crust forms)
  • Convergent (trenches and continental collision
    zones - crust is destroyed)
  • Transform faults (crust is conserved)

12
Arctic Sea Ice analogy
  • Ice crust
  • Whats the main difference?

13
So, how fast, how long?
  • Indonesian earthquake and tsunami of 26 Dec 2005
  • For next time, think about recurrence interval
    and public policy

14
So, how fast, how long?
  • At 74 mm/y, how long to accumulate 15 m of slip?
  • Recurrence interval of 202 y
  • Time since last great earthquake in this area
    (1833) 171 y
  • What physical reason, combined with the nature of
    plate motions, explains why the largest
    earthquakes take place along convergent margins?
  • Subduction zones create the greatest earthquakes
    because they are colder and more rigid than other
    types of plate margins
  • Why did the tsunami warning system originally in
    Pacific?
  • Sites of population centers

15
Geologic Processes and Time
  • Many different time scales
  • Geologic time and time scale
  • 4.5 Ga is a long time!
  • What is the time-scale for mantle convection?
    Consider the life span of the ocean floor from
    ridge to trench How wide? How fast? gtgt How long?

16
Summary
  • Earth is a differentiated, active planet
  • Differences in properties for major parts
  • Density, mechanical, chemical
  • Internal and external energy drives
  • Time is a key consideration
  • Material properties lead to different time scales
    (atmosphere to oceans to solid earth)
  • 4.5 billion years is a long time! (therefore,
    even slow processes such as mantle turnover can
    take place many times)
  • Plate tectonics Unifying theory of global
    geology
  • Reflects the mantle ridding itself of heat
  • Rigid plates with three distinct types of
    boundaries
  • Fits, and predicts, many kinds of features

17
Lectures 3 and 4 Minerals and Fluids--The
Building Blocks
  • Weve seen that the Earth was formed from many
    chemical elements But what do they form and why?
    minerals and fluids
  • What are minerals?
  • What are their properties and how do we identify
    them?
  • Why are they important?

18
Minerals and Fluids Building Blocks of Rocks
  • Minerals and other Earth materials
  • Chemistry elements, valence, chemical bonds
  • Mineral groups structure and composition
  • Mineral properties identification and
    understanding
  • Mineral stability what minerals can tell us

19
Minerals
  • Naturally occurring
  • Not synthetic, artificial
  • Solid crystalline substance
  • Neither liquids nor gases
  • Crystalline Atoms arranged in orderly,
    repeating, 3-D array
  • Generally inorganic
  • Coal not a mineral
  • Calcite in oyster shells and phosphate in teeth
    are minerals (secreted)
  • With a specific chemical composition
  • Fixed or within a range, limited by crystal
    structure

20
Definition of Mineral
Giant gypsum crystals, Naica, Chihuahua
  • Naturally occurring
  • Not synthetic / artificial
  • Crystalline substance
  • Neither liquids nor gases
  • Crystalline atoms arrangedin regular,
    repeating, 3-D array
  • Typically inorganic (on Earth)
  • Coal not a mineral
  • Calcite in oyster shells and phosphate in teeth
    are minerals (secreted)
  • With a specific chemical composition
  • Fixed or within a range (with a fixed ratio),
    limited by the structure of the crystal (e.g., C,
    SiO2, (Mg,Fe)2SiO4, CaCO3)

21
Chemical make-up of the solid Earth
  • Good to know the most abundant elements in the
    core, mantle, crust (hint, hint...)
  • These ( H and C) are the building blocks of the
    common minerals that make up most rocks the
    rock-forming minerals

22
Earth (and Planetary) Materials
  • Solids
  • Fluidsliquids and gases
  • Inorganic and organic

23
Key questions about minerals
  • Why are they important?
  • Building blocks of the solid earth
  • Mineral properties and behavior govern the way
    much of the Earth behaves
  • What do we need to learn about them?
  • Major kinds of rock-forming minerals
  • Their physical properties and how these can be
    related to their compositions and internal
    structure
  • How to identify them (mainly lab)
  • Where (and why) they occur and their geologic
    significance (later lectures)

24
Non-Crystalline Materialseverything else
  • Amorphous solids (without formnon-crystalline)
  • Glass, opal
  • Fluids
  • Gases
  • Aqueous solutions
  • Melts
  • Organic materials

25
A short review of some basic chemistry
26
  • Atomic make-up
  • Recall nucleosynthesis and origin of elements
  • Electrons key for chemistry
  • Electrons transferred in bonds

Different isotopesdifferent number of protons
27
  • Relative size and typical charge (valence) are
    key features charge balance and coordination
    number

28
Chemical reactions construct materials
  • Typically by exchange (ionic bonds) or sharing
    (covalent) of electrons

29
Chemical Bondsbuilding minerals and fluids
underlies properties
  • Bonds form from sharing electrons leading to an
    attraction between atoms
  • Types and characteristics
  • Ionic (electrons mostly transferred, but
    localized)
  • Covalent (electrons shared locally)
  • Metallic (electrons shared throughout structure)
  • Van der Waals Hydrogen (weak or transient
    sharing of electrons)
  • Nature of bonding is underlies physical and
    chemical behavior, including crystal structures

30
Mineral structures and properties
31
Ions Cluster as Polyhedra Why?
  • Opposite charges attract
  • that go around central ion depends on relative
    size
  • Does the central ion have charge or charge?
    Why?
  • Examine the tetrahedron next (coordination 4)

32
SiO4-4
  • Building block of silicate minerals

33
  • Tetrahedral coordination, as in diamond
  • In this case, purely covalent

34
Making a crystal from polyhedra
  • Linking polyhedral units by sharing of some or
    all corners builds a regularly repeating 3-D
    structure a crystal structure

35
Building a crystal by stacking many unit cells
(repeating units)
  • Stacking the unit cubes can give many forms, here
    an octahedron (gem crystal, 0.5 carat in size,
    is from South Africa)

36
External characteristics of crystals
  • Regular geometry of crystals symmetry
  • Crystal faces (growth surfaces)
  • Physical properties (e.g., cleavage planes of
    breaking)
  • Both reflect the underlying crystal structure

37
  • Angular relationships are key distinguishing
    features--not relatives sizes, elongation, etc.
  • Halite 90 degrees cubic
  • Quartz 120 degrees hexagonal

38
  • Galena (lead sulfide) and halite (common salt,
    sodium chloride) have the same crystal
    structures thus, similar forms and cleavages
    (why might other properties differ?)

39
  • Crystal structure of halite (NaCl, common salt)
  • Octahedron, 6 sides in 3-D 6 Cl about 1 Na

40
Tools for Mineral Identification and Studywidely
used in other fields, such as materials science
  • Hand lens (loupe)
  • Petrographic microscope
  • X-ray diffraction
  • Electron microscopy
  • Microbeam analysis
  • Spectroscopy (infrared, visible)
  • Importance . . .

41
Electron Microscope Image of PbS
42
Physical Properties of Minerals
  • Physcial properties
  • Physical characteristics and how minerals respond
    to physcial forces and fields
  • They are important for
  • Identification
  • Understanding Earth processes
  • Practical and esthetic applications
  • Physical properties reflect both composition
    (bonding) and symmetry
  • What types of properties can you think of?

43
Some Key Physical Propertieskey to
identification and to behavior in the Earth
  • Density (mass / volume)
  • Response to force
  • hardness
  • elastic-brittle-ductile behavior
  • cleavage and fracture
  • Interaction with light
  • color (many origins)
  • refraction and dispersion
  • Electrical and magnetic properties
  • more next lecture now systematic mineralogy

44
Systematic Mineralogy
  • Non-silicate minerals
  • Classified by anion elements, oxides, sulfides,
    carbonates, sulfates, phosphates . . .
  • Silicate minerals
  • Classified by SiO44- polymerization framework,
    sheet, chain (single and double), orthosilicates

45
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46
Non-silicates - many typesexcept for elements,
defined by anion
  • Native elements
  • Sulfides (S-2)
  • Oxides (O-2)
  • Halides (Cl-, F-)
  • Carbonates (CO3-2)
  • Sulfates (SO4-2)
  • Phosphates (PO4-3)

What do you see? What is this mineral?
47
  • Halite, a chloride what are some oxide
    minerals? of iron? of hydrogen?

48
  • Hematite Fe2O3
  • 6-fold symmetry, an iron rose
  • This is the most oxidized form of iron (other
    valences?)
  • Where would you expect to find hematite (and most
    Fe3) in the Earth -- in the core, the mantle, or
    the crust?

49
Apatite Ca5(PO4)3F a phosphate
  • Tetrahedral PO4-3 groupis the anion in
    phosphates
  • Location of most phosphorous in rocks(an
    essential nutrient)
  • Where is most of the phosphorous in this
    room?(and why are calcium and fluoride
    important?)

50
Silicate Minerals(some analogies with organic
compounds built of C, H, etc.)
  • Constructed of SiO44- tetrahedra that share 0 to
    4 of their corners with other tetrahedra
  • With all shared?SiO2 (quartz) a framework
    silicate (3-D connections)
  • With fewer shared or with some Al3 substituted
    for Si4, we need to charge balance with other
    ions typically Na, K, Mg, Ca, Fe, Al, H
  • With fewer than 4 corners shared we get sheet,
    double chain, single chain, and orthosilicates
  • Similar relationships apply in silicate melts

51
SiO4-4
  • Building block of silicate minerals

52
  • The main groups of silicate units that make up
    most silicate minerals progressively greater
    polymerization (joining) of SiO4-4 tetrahdra
  • Isolated, single and double chain, sheet,
    framework
  • Next Tuesday and in lab, we look at these mineral
    groups and their physical properties

53
Major Silicate Mineral Groups(examined in lab,
used repeatedly later)
  • Mafic minerals (Mg-Fe silicates)
  • Olivine isolated SiO4
  • Pyroxenes single chain
  • Amphiboles double chain
  • Micas sheet
  • Clay minerals sheet
  • Felsic minerals (feldspars and silica)
    framework
  • Plagioclase feldspar (Ca-Na)
  • Potassium feldspar (K)
  • Quartz

54
Next Time
  • Mineral groups structure and composition
  • Emphasis on silicates
  • Mineral properties identification and
    understanding
  • Mineral stability what minerals can tell us
  • Review Chapter 3 as preparation for lab next week
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