FAR WEST LAVAS

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images from Jennifer Whitten and colleagues 2011 and Journal of Geophysical Research

Twenty years or so ago scientists who tried to understand the Moon could only use black and white photographs.
Now, as depicted here, there are multiple types of data to aid interpretations. A recent investigation by Jennifer
Whitten at Brown University and colleagues of the sparse lavas in the Orientale Basin considered multispectral
images (left) that provided compositional information, high resolution images allowed mapping (center) of sinuous
rilles (red) and domes (yellow), and age estimates from crater counting (right). All of these data sets came from
the Moon Mineralogy Mapper. Topographic data were included from the LRO laser altermeter (LOLA). With all
these resources Jennifer's team determined that the first lavas erupted in the basin center - Mare Orientale itself -
about 100 million years after the basin formed. That difference in timing shows that the mare lavas did not form
as a result of pressure release - excavating trillions of tons of lunar crust greatly reduces the pressure. Following
eruptions moved to the northeast, first to Lacus Veris and finally at Lacus Autumni. Remarkably, crater counts
suggest that the Autumni lavas may be amongst the youngest lavas on the Moon with ages of 1.7 billion years.
And also, the age range of 1.9 b.y. is huge, for such a small volume of lavas in just one basin. Interestingly, the
younger lavas are progressively further from the basin center and are at higher elevations. This is consistent with
the idea that stresses and crustal fractures propagate outward with time as the basin topography completes adjust-
ments. These are good findings that help us understand the evolution of basin volcanism. At Imbrium and other
basins where lavas bury all of the basin floor the history is lost.

Chuck Wood

Related Links
Jennifer Whitten, James W. Head, Matthew Staid, Carle M. Pieters, John Mustard, Roger Clark, Jeff Nettles, Rachel
L. Klima and Larry Taylor (2011) Lunar mare deposits associated with the Orientale impact basin: New insights into mineralogy, history, mode of emplacement, and relation to Orientale Basin evolution from Moon Mineralogy Mapper (M3) data from Chandrayaan‐1. JOURNAL OF GEOPHYSICAL RESEARCH 116, E00G09, doi:10.1029/2010JE003736.


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