Transcript The Concepts of Maria - Lunar and Planetary Laboratory

Yen-Shan Lim
PTYS 395
October 16, 2008
The Concepts of Maria
• Maria – dark, smooth, low plains (occupy 16% of the lunar
surface area)
• Before space age, concepts for the models of maria:
- Dried-up riverbeds
- Huge bowls of dust
- Flow of volcanic ash
- Melted material ejected from basin
• The Face of the Moon (1949) : Maria were floods of basalt
• Basalts sample returned (4.3 to 3.1 billion years old)
- Oldest rocks on Earth: 4.5 billion years old)
The two basic types of regions on the Moon: a smooth, dark maria on
the left and a heavily-cratered, light-colored highland region on the
upper right.
Lunar Lava Flows
• At close-up scales, small, lobe-shaped scarps can be seen (common in
the lava flows of basalt found on Earth)
• Ranger 7 spacecraft returned close-up pictures of the Moon
- Scale of impact cratering continues downward to the limits of
resolution
- Maria are covered by the regolith
• Lunar Orbiter spacecraft  landforms
• Surveyors 1, 3, 5 and 6 give a close-up view of the surface of the
maria: dark rocks covered with small holes
• Samples of maria (Apollo missions)  basalt
• Basalt
- dark lava
- Iron and magnesium
- Very fine (usually <1mm)
Lunar lavas  small, bubble-like holes (vesicles)
Mare basalt
• Lunar lavas:
- devoid of water
- depleted in all volatile elements (very low bp.)
• 1st basalts returned were from Mare Tranquilitatis
 large amounts of titanium
• Lavas (Moon): contain minor minerals not found in
Earth rocks  armalcolite (another
iron titanium mineral)
• The viscosity of erupted lunar lava depends on the
composition and temperature of the magma
• ↓ aluminum and alkali, ↑ iron, ↑ temperature at
extrusion  ↓viscosity of lavas
• Mare lavas tend to form low, broad structures volcanoes
• Lavas from Apollo 12 (formed ~ 3.1 billion years ago)
- lower titanium than the Apollo 11 basalts
- 600 to 700 million years younger
- low in volatile elements, very rich in irons
• Apollo 15  low-titanium basalts, slightly older than those
from Apollo 12 (3.3 billion years ago)
• Apollo 17  very high titanium basalts (3.7 billion years old)
• Conclusion: Early eruptions of high-titanium lavas and late
eruptions of low-titanium lavas
• How lava is formed?
- The high density of mantle is made up of olivine and
pyroxene
- Radioactive, heat-producing elements made the early
mantle very hot
- Some places are partially melt
- Blobs of melt coagulate deep in a planet’s interior and
slowly migrate upwards
- Force their way to the surface
- Extruded onto the surface as lava flow
Fire Fountain
• Small glass beads were found in abundance at Apollo 15
and 17 sites
 clear emerald-green glass (Apollo 15 site)
 black and orange glass (Apollo 17 site)
• The surfaces of these glass beads have small glassy
mounds made up of a variety of volatile elements (lead,
zinc, and halogens)
• Apollo 15 glasses (rich in magnesium, low in titanium)
• Apollo 17 glass (rich in titanium)
• The glasses  products of a spray of low-viscosity lava into
space
• Hawaii  eruptions of lava are accompanied by very large sprays
of magma from the vent
• Such spray eruptions are called fire fountains  ash deposit
around the eruptive vent
• Lunar glasses : products of fire fountains on the Moon over 3
billion years ago
• Large craters on the Moon have deformed and fractured floors
• Along some fractures are small irregular craters surrounded by
a dark, smooth material
• These craters  volcanic vents surrounded by ash deposits.
• Pockets of gas and other volatile elements existed deep
with the Moon
• Vesicles are found in some samples of mare basalt
• Composition of this gas phase
 not water vapor (absence of water-bearing phase)
 reduced chemistry of lunar lavas
(gas phase might be the carbon monoxide)
References
Mare Basalt
http://images.google.com/imgres?imgurl=http://pds.jpl.nasa.gov/p
lanets/images/browse/earth/basalt.jpg&imgrefurl=http://pds.jpl.na
sa.gov/planets/captions/earth/basalt.htm&h=400&w=400&sz=22
&hl=en&start=5&usg=__S3ND7NoLEUyrS1PAFy4ox9rrSv0=&t
bnid=CYDXdySqeDWDaM:&tbnh=124&tbnw=124&prev=/imag
es%3Fq%3Dbasalt%2Bon%2Bthe%2Bmoon%26gbv%3D2%26hl
%3Den%26sa%3DG
Tomography of Lunar Spherules
http://images.google.com/imgres?imgurl=http://research.amnh.org/~debe
l/tomo-aps/HIfirefountain1cropLogo.gif&imgrefurl=http://research.amnh.org/~debel/to
moaps/lunarOG1.html&h=561&w=742&sz=259&hl=en&start=5&usg=__c
QjFAo0pEWBztXrgYXTajcfWyo=&tbnid=tGw8tTQsv00CuM:&tbnh=107
&tbnw=141&prev=/images%3Fq%3Dfire%2Bfountain%2Bon%2Bthe%
2Bmoon%26gbv%3D2%26hl%3Den%26sa%3DG
Meet the Neighbour
http://images.google.com/imgres?imgurl=http://www.spacegazer.com/images/photos/s
smay05moon.jpg&imgrefurl=http://www.spacegazer.com/may-2005g.asp&h=462&w=480&sz=38&hl=en&start=14&usg=__PAxFKqSz5IAOvDZEAqiK
7gdYvDo=&tbnid=EgxDkeyU2ZdlnM:&tbnh=124&tbnw=129&prev=/images%3Fq%
3Dmaria%2Bon%2Bthe%2Bmoon%26gbv%3D2%26hl%3Den%26sa%3DG
http://images.google.com/imgres?imgurl=http://www.windows.ucar.edu/the_universe/i
mages/maria_5x5.gif&imgrefurl=http://www.windows.ucar.edu/tour/link%3D/earth/i
mages/maria_5x5.html&h=504&w=431&sz=241&hl=en&start=25&usg=__TfcTAraq
K5RsXiOiRMcih0gPofc=&tbnid=hlIRS2DcUESmgM:&tbnh=130&tbnw=111&prev=
/images%3Fq%3Dmaria%2Bon%2Bthe%2Bmoon%26start%3D18%26gbv%3D2%26
ndsp%3D18%26hl%3Den%26sa%3DN
Spudis (The Once and Future Moon) Chapter 5