GEOL 3045: Planetary Geology

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GEOL 3045 Planetary Geology

• Lysa Chizmadia
• Formation of the Moon

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Lunar Eclipses
Images from http//en.wikipedia.org/wiki/Lunar_e
clipse
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20 Feb 2008
http//sunearth.gsfc.nasa.gov/eclipse/LEmono/TLE20
08Feb21/TLE2008Feb21.html
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Formation Theories

• Fission Moon was originally part of the Earth
  somehow separated early
• Problem compositions not enough
• Capture Moon was created somewhere else and
  captured by Earths gravity
• Problem O-isotopes identical
• Mutual Accretion They both formed together out
  of the same materials
• Problem Moon has little or no core
• Big Splash Mars-sized bolide hit Earth Moon
  formed from ejecta ring
• Fits O-isotopes, trace elements low density of
  Moon

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Big Splash (1/3)

• Impactor size of Mars
• Called Tethys
• Collided 4.4 Ga
• Sprayed crust some of mantle into space
• Both proto-Earth Tethys molten
• Core of impactor incorporated into Earths core

Images from http//www.psi.edu/hartmann/pic-cat/e
arth.html
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Big Splash (2/3)

• Ejecta from impact forms ring around molten Earth
• Both have magma oceans
• Ring coalesces into Moon
• Crust of both bodies cool down
• No longer magma oceans
• Moon sweeps up rest of ring material

Images from http//www.psi.edu/hartmann/pic-cat/e
arth.html
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Big Splash (3/3)

• Volcanism on Moon
• Late Heavy Bombardment
• Volcanism subsides on Moon

Images from http//www.psi.edu/hartmann/pic-cat/e
arth.html
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Late Heavy Bombardment

• 3.8 - 4.1 Ma
• Basin-forming impacts on Moon, Earth, Mercury,
  Venus, Mars
• E.g. Caloris Basin, Mare Basins
• Materials sent in to inner solar system by
  perturbations from Giant Planets

Image from http//www.daviddarling.info/encyclop
edia/L/late_heavy_bombardment.html
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Lunar Volcanism

• Mare Volcanism
• Most 3.5 - 3.0 Ga
• Ages range from 4.2 to 1.2 Ga
• Occurs mostly on near side
• Classification
• High Ti basalt
• Low Ti basalt
• Very low Ti basalt
• Ti-rich Orange glass
• 3.7-3.8 Ga

Images from http//www.psrd.hawaii.edu/Dec00/hig
hTi.html
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KREEP

• K Potassium
• REE Rare Earth Elements
• P Phosphorus
• Formed as a result of magma ocean
• Heavy minerals (e.g. olivine, pyroxene) sank
• Light minerals (e.g. Plagioclase) rose
• Fractional Crystallization made magma KREEP-rich
• KREEP incompatible

Images from http//www.lunarpedia.org/index.php?t
itleKREEP
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Summary

• Formed from Big Splash
• Problems with other models
• Moon Earth composition, but not identical
• Moon has low density
• Moon Earth have same O-isotopes
• Heavy Late Bombardment
• Perturbations from Giant Planets
• Lunar Volcanism
• Ti important element
• KREEP
• Leftovers from fractional crystallization of
  magma ocean