Earth, Moon and Mars: How They Work

1
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
2
(No Transcript)
3
MOON Mass 1.23 of Earths R 1737 km (27.3
of Earths) g 16.5 of Earths day 29.5 Earth
days atmosphere none (though there is sodium
exosphere)
4
(No Transcript)
5
Clementine spectral reflectance Lucey et al.
(1995)
mare basalt
highlands anorthosite
nearside telescopic
nearside FeO
high FeO (red white) mare basalt
dark mare basalt
6
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
7
Lack of erosion allows understanding of cratering
process
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
Giant-impact model for formation of the
Moon(artists depictions!)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
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
17
all or mostly molten magma ocean
core
O, Mg, Al, Si Ca, Ti, Fe
18
olivine pyroxene sink
Al Ca
Mg Fe
19
plagioclase floats!
Al Ca
liquid
solid
Mg, Fe, Ti
20
anorthosite crust (Al, Ca)
incompatible elements (K, P, Y, Zr, La, Th, U,
many others)
ultramafic mantle (Fe, Mg, Ti)
oversimplified textbook model
21
melt volume of biggest basin-forming impacts
anorthosite crust (Al, Ca)
50 km
trapped
residual
liquid
ultramafic mantle (Fe, Mg, Ti)
22
impact basin
moon
anorthosite crust
trapped
residual
liquid
ultramafic mantle
23
mare basalt(Fe, Mg, Ti)
anorthosite crust (Al, Ca)
50 km
trapped
residual
liquid
alias KREEP
ultramafic mantle
partial melting in mantle
24
(No Transcript)
25
Formation of the Earliest Crust, 1
26
Formation of the Earliest Crust, 2
27
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
28
Fig. 5-5 from Papike J.J., Ryder G., and Shearer
C. K. (1998) Chapter 5. Lunar Samples. In
Reviews in Mineralogy, Vol. 36, Planetary
Materials (ed. J. J. Papike), pp. 5-15-234,
Mineralogical Society of America, Washington.
29
Global View Crustal Thickness
Near Side
Crust-mantle boundary near Mare Cognitum
40 km
Far Side
Khan et al., 2000
M. Wieczorek
30
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
31
From Jolliff et al., 2000, JGR
32
FHT-SPA
From Jolliff et al., 2000, JGR
33
Origin of Compositional Asymmetry

• Formation and distribution of igneous rock
  types
• consistent w/ magmasphere hypothesis
• with modifications
• Anorthositic crust absent from Procellarum
  KREEP Terrane
• Stripped by early impact
• or non-uniform solidification of Magma Ocean
  resulted in..
• Anorthositic protocontinent
• KREEPy residual sea

34
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

35
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
36
approximate mean surface of feldspathic highlands
X
37
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)
38
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
39
lunar meteorite MacAlpine Hills 88105
both these rocks are regolith breccias
Apollo 16 sample 60019
40
Apollo 11
regolith breccia
2 mm
impact-glass spherule
impact-melt breccia
anorthosite
soil-coated basalt
feldspathic breccia
basalt
41
regolith (soil)
42
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
43
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
44
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
45
solar wind
regolith (soil)
He2
H
46
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
47
LaPaz Icefield 02205 1226 grams Antarctica
Miller Range 05035 142 grams Antarctica
basalts
LaPaz Icefield 02226 244 grams Antarctica
48
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
49
lunar mineralogy
mare nonmare
plagioclase pyroxenes olivine ilmenite
all mineral data from Papike, Ryder, Shearer
(1998)
Al2O3 ()
50
lunar mineralogy
anorthite
soils
regoliths from Apollo and Luna missions
Al2O3 ()
Earths crust
pyroxene
olivine
51
lunar mineralogy
anorthite
highlands
lunar meteorites
Al2O3 ()
maria
pyroxene
olivine
52
Al2O3 ()
Fe2O3 MgO ()
53
Crustal Igneous Rock Suites

• Ferroan Anorthosite
• Early plagioclase flotation crust
• Magnesian Suite
• Typical plutonic-magmatic fractionation trends
• Some have KREEP-enriched parent magmas
• Alkalic Suite
• Extended fractionation (granite, monzogabbro/QMD)
• Possible relation to Mg-Suite

54
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.
55
Crustal Rock Ages
56
Lunar Terranes FeO
57
all lunar meteorites
feldspathic highlands
near side
mixed provenance and brecciated nonmare norites
Al2O3 ()
mare
far side
Clementine Lucey et al. (1995)
58
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
59
Lunar Terranes Thorium
60
all lunar meteorites
near side
mare
far side
feldspathic highlands
Lunar Prospector Lawrence et al. (2000)
61
all lunar meteorites
SaU 169 IMBrx
near side
SaU 169 RegBrx
mare
far side
feldspathic highlands
Lunar Prospector Lawrence et al. (2000)
62
(No Transcript)
63
Moons magnetic field From core? Impacts? Is
Core iron or titanium-rich silicate?
64
Moonquakes
65
(No Transcript)
66
(No Transcript)
67
Comparison of Earthquake and Moonquake
68
Bottom of magma ocean? Compositional boundary
between olivine-rich and pyroxene-rich
silicates? Maximum depth of melting of mare
source region?
69
Figure 3-14a
70
(No Transcript)