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Lunar volcanism: dating of meteorite Kalahari 009 6 December 2007

Posted by admin in lunar volcanism, Moon.
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Precision dating of a lunar meteorite indicates that the Moon was volcanically active hundreds of millions of years earlier than was previously thought, reports the BBC. A study published in the journal Nature gives a date of 4.35 plus/minus 0.15 billion years. The small quantities of basaltic lunar rocks collected during manned exploration of the Moon date to around 3.9 billion years. From the BBC report:

Volcanoes were active on the Moon’s surface soon after it was formed, a new study in the journal Nature suggests. Precision dating of a lunar rock that fell to Earth shows our satellite must have had lava erupting across its vast plains 4.35 billion years ago. This is hundreds of millions of years earlier than had been indicated by the rocks collected by Apollo astronauts.

The paper, ‘Cryptomare magmatism 4.35 Gyr ago recorded in lunar meteorite Kalahari 009’, by Kentado Terada (Hiroshima University), Mahesh Anand (Open University) et al, is in Nature, no. 450 (6 December 2007), pp. 849-852. Abstract (references removed):

The origin and evolution of the Moon remain controversial, with one of the most important questions for lunar evolution being the timing and duration of basaltic (mare) magmatism. Here we report the result of ion microprobe U–Pb dating of phosphates in a lunar meteorite, Kalahari 009, which is classified as a very-low-Ti mare-basalt breccia. In situ analyses of five phosphate grains, associated with basaltic clasts, give an age of 4.35 plusminus 0.15 billion years. These ancient phosphate ages are thought to represent the crystallization ages of parental basalt magma, making Kalahari 009 one of the oldest known mare basalts. We suggest that mare basalt volcanism on the Moon started as early as 4.35 Gyr ago, relatively soon after its formation and differentiation, and preceding the bulk of lunar volcanism which ensued after the late heavy bombardment around 3.8-3.9 Gyr. Considering the extremely low abundances of incompatible elements such as thorium and the rare earth elements in Kalahari 009 and recent remote-sensing observations illustrating that the cryptomaria tend to be of very-low-Ti basalt type, we conclude that Kalahari 009 is our first sample of a very-low-Ti cryptomare from the Moon.

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