ISSN:
1573-0794
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract Green spherules from the ‘clod’ 15426 and from fines 15421 contain about 100 times less trapped inert gases than normal bulk fines from Apollo 15. These spherules have apparently never been directly exposed to the solar wind. Spherules from other fines contain about 10 times more trapped gas than those from the ‘clod’. The gas in the former is surface correlated. However, spherules from fines 15401 are exceptionally gas-poor. (He4/Ne20) T in all spherules is commonly less than 10, which implies severe He4 losses. (Ne20/Ar36) T on the other hand is nearly always greater than 10; and ranges up to 20.3. The Ne21 C and Ar38 C radiation ages vary from 22 to 750 × 106 yr, but most of them lie in the range 200–400 × 106 yr. He3 C ages are always much younger, owing to He3 C losses. The trapped gases can be of solar-wind origin, but this origin requires a two-stage model for the spherules from the clods. First, solar wind was trapped in a parent material, from which the spherules were formed, presumably by impact melting. When the spherules were formed, some fraction of the original gas was retained by them. Another possibility is that the gases were absorbed from an ambient gas phase. The trapped gases may also be assumed to represent primordial lunar gas. The composition of this gas is then similar to the ‘solar’ or ‘unfractionated’ component of gas-rich meteorites, but unlike that in most of the carbonaceous chondrites. The Ar40-Ar36 systematics show two families of spherules: those from 15426 and 15421 which define a line with slope of about 4–5; and those from the fines which fall near a line with slope of about 1.4–1.9. Both lines have similar Ar40-intercept-values of about 3–9 × 10−6 cm3 STP g−1 of Ar40. The corresponding K-Ar40 age can be as old as 4300 or as young as 2500 × 106. The gas content of the spherules from fines suggests strongly that all spherules were at one time in ‘clod’-like material. This, in turn, seems to imply that a body or layer of ‘cloddy’ material like 15426 was, and perhaps still is present in the Apollo 15 landing area. Cone Crater impact has tapped this body, but has probably not produced the ‘clods’. The green material may have been transported to the Apollo 15 site from elsewhere either as impact-ejecta or by a volcanic eruption. Our results do not permit a choice between the two possibilities.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00578812
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