Yen-Shan LimPTYS 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 Basalthttp://images.google.com/imgres?imgurl=http://pds.jpl.nasa.gov/planets/images/browse/earth/basalt.jpg&imgrefurl=http://pds.jpl.nasa.gov/planets/captions/earth/basalt.htm&h=400&w=400&sz=22&hl=en&start=5&usg=__S3ND7NoLEUyrS1PAFy4ox9rrSv0=&tbnid=CYDXdySqeDWDaM:&tbnh=124&tbnw=124&prev=/images%3Fq%3Dbasalt%2Bon%2Bthe%2Bmoon%26gbv%3D2%26hl%3Den%26sa%3DG

Tomography of Lunar Spheruleshttp://images.google.com/imgres?imgurl=http://research.amnh.org/~debel/tomo-aps/HI-firefountain1cropLogo.gif&imgrefurl=http://research.amnh.org/~debel/tomo-aps/lunarOG1.html&h=561&w=742&sz=259&hl=en&start=5&usg=__cQ-jFAo0pEWBztXrgYXTajcfWyo=&tbnid=tGw8tTQsv00CuM:&tbnh=107&tbnw=141&prev=/images%3Fq%3Dfire%2Bfountain%2Bon%2Bthe%2Bmoon%26gbv%3D2%26hl%3Den%26sa%3DG

Meet the Neighbourhttp://images.google.com/imgres?imgurl=http://www.spacegazer.com/images/photos/ssmay05moon.jpg&imgrefurl=http://www.spacegazer.com/may-2005-g.asp&h=462&w=480&sz=38&hl=en&start=14&usg=__PAxFKqSz5IAOvDZEAqiK7gdYvDo=&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/images/maria_5x5.gif&imgrefurl=http://www.windows.ucar.edu/tour/link%3D/earth/images/maria_5x5.html&h=504&w=431&sz=241&hl=en&start=25&usg=__TfcTAraqK5RsXiOiRMcih0gPofc=&tbnid=hlIRS2DcUESmgM:&tbnh=130&tbnw=111&prev=/images%3Fq%3Dmaria%2Bon%2Bthe%2Bmoon%26start%3D18%26gbv%3D2%26ndsp%3D18%26hl%3Den%26sa%3DN

Spudis (The Once and Future Moon) Chapter 5