Earth, Moon and Mars: How They Work

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Earth, Moon and Mars How They Work
Professor Michael Wysession Department of Earth
and Planetary Sciences Washington University, St.
Louis, MO (with thanks to Brad Joliff, Randy
Korotev, Mark Wieczorek) Lecture 10 The Moon
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Larry Haskin, Lunar Geochemist
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michael_at_seismo.wustl.edu
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MOON Galileo (1609) - 400th Anniversary!!!!
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MOON Johannes Hevelius (1647)
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MOON La Voyage Dans La Lune (1902)
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Clementine spectral reflectance Lucey et al.
(1995)
mare basalt
highlands anorthosite
nearside telescopic
nearside FeO
high FeO (red white) mare basalt
dark mare basalt
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6 Apollo missions on which samples were
collected 1969 1972 382 kg of
samples 3 Luna missions (Russia) 1970
1976 0.32 g of samples
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This is a 35 million year old impact crater on
Earth.
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Lack of erosion allows understanding of cratering
process
Moon about 500,000 craters gt 1 km
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Giant-impact model for formation of the
Moon(artists depictions!)
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Internal Structure

• Differentiated Crust and Mantle
• Feldspathic Crust
• Ultramafic CumulateMantle
• Small Core
• Layered Crust
• Al-rich upper crust
• KREEP zone
• Mafic (Fe, Mg-rich) lower crust
• Impact and volcanic modification

Impact Basin
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Anorthosite 90 Plagioclase Feldspar (Pyroxene
and Olivine have been removed!)
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all or mostly molten magma ocean
core
O, Mg, Al, Si Ca, Ti, Fe
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olivine pyroxene sink
Al Ca
Mg Fe
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plagioclase floats!
Al Ca
liquid
solid
Mg, Fe, Ti
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anorthosite crust (Al, Ca)
incompatible elements (K, P, Y, Zr, La, Th, U,
many others)
ultramafic mantle (Fe, Mg, Ti)
oversimplified textbook model
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Rocks crystallize at different temperatures See
this in the Palisades Cliffs (a 200 million year
old sill) in New Jersey, along the Hudson River.
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Figure 3-14a
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melt volume of biggest basin-forming impacts
anorthosite crust (Al, Ca)
50 km
trapped
residual
liquid
ultramafic mantle (Fe, Mg, Ti)
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impact basin
moon
anorthosite crust
trapped
residual
liquid
ultramafic mantle
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mare basalt(Fe, Mg, Ti)
anorthosite crust (Al, Ca)
50 km
trapped
residual
liquid
alias KREEP
ultramafic mantle
partial melting in mantle
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Similar to pressure release melting on Earth at
mid-ocean ridges
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• Maria Basalts
• Most 3.5 - 3.0 Ga
• Oldest 4.2 Ga
• Youngest 1.2 Ga (from crater counts)

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Formation of the Earliest Crust, 1
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Formation of the Earliest Crust, 2
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Interior Evolution Asymmetry Mantle Overturn

• Asymmetry involves mantle heat sources.
• Production of secondary crust tied to locus of
  radioactive heat-producing elements
• Cumulate mantle overturn may have been
  localized.
• Root cause unknown
• Degree-1 downwelling
• Early very large (Procellarum) impact basin?

Magnesian-suite Intrusives
Residual KREEP pockets
Mixing
Sinking of Fe Ti-rich minerals
KREEP-rich residuum - localized
overturn
Mg-rich cumulates
Sinking of Fe Ti-rich minerals
KREEP-rich residuum - localized
overturn
Near side
Far side
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Global View Crustal Thickness
Near Side
Crust-mantle boundary near Mare Cognitum
40 km
Far Side
Khan et al., 2000
M. Wieczorek
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Global View Crustal Thickness
Near Side
Northeast of SPA (104 km)
Apollo Basin (0 km)
Far Side
M. Wieczorek
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South Pole-Aitken Basin

• Largest Impact basin on Moon
• 2200 km diameter
• Same size as Hellas on Mars
• Age unknown, but from geologic
  relationships, is the oldest of large
  lunar impact basins.
• Possibly exhumed lower crust

Geologic cross section
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• Gravity Field (Lunar Prospector) - shows mascons
  (positive gravity anomalies)
• Some associated with impact basins (basaltic
  fill)
• Some not associated with impact basins (igneous
  intrusions?)

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From Jolliff et al., 2000, JGR
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FHT-SPA
From Jolliff et al., 2000, JGR
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Lunar Mineralogy

• Minerals provide keys to understanding lunar
  rocks because their compositions and atomic
  structures reflect formation conditions.
• Lunar minerals are anhydrous no water!
• Lunar minerals mostly formed at low pressure

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lunar mineralogy
Only 4 minerals account for 98 of the Moons
crust!
typical volume (mode)
maria
plagioclase pyroxene olivine ilmenite total
85 10 5 0.3 100
36 53 6 5 100
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lunar mineralogy
Only 4 minerals account for 98 of the Moons
crust!
typical volume (mode)
maria
plagioclase pyroxene olivine ilmenite total
85 10 5 0.3 100
36 53 6 5 100
Ilmenite - FeTiO3 - source of water, as well as
Fe and Ti!
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approximate mean surface of feldspathic highlands
X
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plagioclase composition
Na
Ca
CaAl2Si2O8
NaAlSi3O8
0
10
20
30
40
50
60
70
80
90
100
albite
oligoclase
andesine
labradorite
bytownite
anorthite
plagioclase in the lunar highlands is
anorthite(typically An95-98)
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meteoroid impact velocity 20-40 km/s
lunar meteorite
lunar escape velocity 2.4 km/s
time from launch to landing lt100 years to 20
million years
lands at terminal velocity 0.1 km/s
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lunar meteorite MacAlpine Hills 88105
both these rocks are regolith breccias
Apollo 16 sample 60019
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Apollo 11
regolith breccia
2 mm
impact-glass spherule
impact-melt breccia
anorthosite
soil-coated basalt
feldspathic breccia
basalt
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regolith (soil)

• 3-5 m in maria
• 10-15 km in highlands
• thicker in older areas
• impact gardening

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Soil Components

• Many rock types make up average soil
• Impact-fused soil Agglutinates
• Reduced Fe metal major effect on optical
  properties
• Highly vesicular
• Abundant, e.g., 50 of some soils
• Volcanic glasses
• Impact-melt glasses and breccias

Jolliff et al., 1996
Apollo 11
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Dhofar 1180 115 grams Oman
Northwest Africa 2200 552 grams Morocco
lunar meteorite regolith breccias
Dhofar 1428 213 grams Oman
Dhofar 1084 90 grams Oman
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volcanic glass spherules
from Apollo 17 regolith sample 71061
Regolith breccias contain lithologies that can
only be produced at or above the lunar surface.
from Apollo 17 regolith sample 76503
agglutinate
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solar wind
regolith (soil)
He2
H
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Allan Hills 81005 31 grams Antarctica
fusion crust
unheated interior
Pecora Escarpment 02007 22 grams Antarctica
Queen Alexandra Range 93069 21 grams Antarctica
regolith breccias
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LaPaz Icefield 02205 1226 grams Antarctica
Miller Range 05035 142 grams Antarctica
basalts
LaPaz Icefield 02226 244 grams Antarctica
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regolith breccia
Sayh al Uhaymir 169 an impact-melt with attached
regolith breccia mass 206 g found 21 February
2004 where Oman
impact-melt breccia
regolith breccia
norite clast
impact-melt breccia
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lunar mineralogy
mare nonmare
plagioclase pyroxenes olivine ilmenite
all mineral data from Papike, Ryder, Shearer
(1998)
Al2O3 ()
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lunar mineralogy
anorthite
soils
regoliths from Apollo and Luna missions
Al2O3 ()
Earths crust
pyroxene
olivine
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lunar mineralogy
anorthite
highlands
lunar meteorites
Al2O3 ()
maria
pyroxene
olivine
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Al2O3 ()
Fe2O3 MgO ()
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Rare Earth Elements
The trivalent REE (3 charge) are incompatible in
major minerals. However, Eu occurs in 2 valence
state. Eu2 is right size and charge to
substitute for Ca, this it is compatible in
plagioclase.
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Crustal Rock Ages
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Lunar Terranes FeO
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all lunar meteorites
feldspathic highlands
near side
mixed provenance and brecciated nonmare norites
Al2O3 ()
mare
far side
Clementine Lucey et al. (1995)
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incompatible trace elements(on the Moon)
P, K, Rb, Y, Zr, Nb, Mo, Cs, Ba, La, Ce, Pr, Nd,
Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W,
Th, U red radioactive
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Lunar Terranes Thorium
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all lunar meteorites
near side
mare
far side
feldspathic highlands
Lunar Prospector Lawrence et al. (2000)
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all lunar meteorites
SaU 169 IMBrx
near side
SaU 169 RegBrx
mare
far side
feldspathic highlands
Lunar Prospector Lawrence et al. (2000)
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Moons magnetic field From core? Impacts? Is
Core iron or titanium-rich silicate?
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Moons magnetic field (from Lunar Prospector)
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Moonquakes
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Apollo Lunar Seismometer
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Effect of lunar and solar tides on Earth
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Effect of lunar and solar tides on Earth Has
changed the rate of rotation rate of Earth! But
how is conservation of momentum conserved?
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Effect of lunar and solar tides on Earth Has
changed the rate of rotation rate of Earth! But
how is conservation of momentum conserved? Moon
is moving away from Earth!
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Effect of lunar and solar tides on Earth Bay of
Fundy
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Comparison of Earthquake and Moonquake
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Bottom of magma ocean? Compositional boundary
between olivine-rich and pyroxene-rich
silicates? Maximum depth of melting of mare
source region?
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• Water at South Pole?
• Shackleton Crater?
• Contained in Regolith?

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Lunar Reconnaissance OrbiterJune 17, 2009 Areas
of investigation to include - Global
topography - Characterization of deep space
radiation - Lunar polar regions, including
possible water ice deposits and the lighting
environment - High-resolution mapping (max 0.5
m) to help in selection of future landing sites
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Lunar CRater Observation and Sensing Satellite
(LCROSS) - Searching for South Pole water
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Gravity Recovery and Interior Laboratory (GRAIL)
mission would use high-quality gravity field
mapping of the moon to determine the moon's
interior structure. Maria Zuber of the
Massachusetts Institute of Technology, Cambridge,
Mass., is GRAIL's principal investigator. NASA's
Jet Propulsion Laboratory, Pasadena, Calif.,
would manage the project.
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