Publication Date:
2019-07-13
Description:
The (Ar-39)-(Ar-40) ages for 21 lunar samples from Apollo 14, 15, 16, and 17 are presented. The cosmic-ray exposure ages, Ca, and K contents are also measured. Mare basalt 15075, a slowly cooled pyroxene-phyric basalt, has a (Ar-39)-(Ar-40) plateau age of 3.45 + or - 0.2 billion years. This is one of the oldest mare basalts found at Apollo 15. 65777, a recrystallized noritic breccia, has a plateau age of 3.72 + or - 0.02 billion years, relatively young for a highland rock. This rock is probably related to a cratering event over 200 m.y. post Imbrium. Similarly breccia 68516 was formed 150 m.y. post Imbrium. Histograms for the (Ar-39)-(Ar-40) plateau ages strongly suggest that the peak in ages at Apollo 14, 16, and 17 of about 4 billion years is caused by the dominance of Imbrium ejecta at these landing sites.
Keywords:
LUNAR AND PLANETARY EXPLORATION
Type:
Lunar Science Conference; Mar 14, 1977 - Mar 18, 1977; Houston, TX
Format:
text
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