September 23, 2014

Pink And Grey Lavas

image by Le Qiao and colleagues, Planetary and Space Science

China has identified the southern part of Mare Imbrium as an area of interest for landing, rover and sample return missions. As part of their investigations to select future landing sites, Chinese scientists have mapped Sinus Iridum, summarizing their results in the map and cross-section above. The different colors of orange-pink and grey represent mare basalt units with different chemistry and mineralogy. Crater counts yielded the ages shown in parentheses - The Em2 Imbrium lavas are 2.50 billion (or giga) years old, and the lavas further north on the floor of Iridum are progressively older. The cross-section shows why - the floor slopes to the north, and each new lava flow was not as extensive as the former ones. This seems a very lucky circumstance! On to another topic: This paper does not address why the southern rim of the Iridum impact crater is missing. As I have proposed before, it probably subsided along a basin edge fault - just as the Ancient Thebit crater did, although there the fault (the Straight Wall) is not buried under lava. The cross-section also does not show the faulting along the inner rim of the Jura Mountains crater rim - the fault should tilt inwards (toward the south) and extend a few kilometers deep. A facing fault for the buried southern rim of the Iridum crater should be shown under the mare ridge just inside the Em2 lava. This new Chinese work advances understanding of the Iridum area but doesn't explain everything.

Chuck Wood

Related Links
21st Century Atlas chart 20.
Le Qiao, Long Xiao, Jiannan Zhao, Qian Huang & Junichi Haruyama (2014) Geological features and evolution history of Sinus Iridum, the Moon. Planetary and Space Science 101, 37–52

Yesterday's LPOD: T-Rex Smile

Tomorrow's LPOD: Black Splash

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