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Evensen, N. M.

Publications and source records attributed to Evensen, N. M..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Rare-earth abundances in chondritic meteorites

Fifteen chondrites, including eight carbonaceous chondrites, were analyzed for rare earth element abundances by isotope dilution. Examination of REE for a large number of individual chondrites shows that only a small proportion of the analyses have flat unfractionated REE patterns within experimental error. While some of the remaining analyses are consistent with magmatic fractionation, many patterns, in particular those with positive Ce anomalies, can not be explained by known magmatic processes. Elemental abundance anomalies are found in all major chondrite classes. The persistence of anomalies in chondritic materials relatively removed from direct condensational processes implies that anomalous components are resistant to equilibrium or were introduced at a late stage of chondrite formation. Large-scale segregation of gas and condensate is implied, and bulk variations in REE abundances between planetary bodies is possible.

Evensen, N. M.↗
NASA NTRS1974

Provenance of KREEP and the exotic component - Elemental and isotopic studies of grain size fractions in lunar soils

Sieve fraction analyses of lunar soils reveal the presence of a fine-grained exotic component enriched in K, Rb, Sr, Ba, and in radiogenic Sr in all soils. The probable source of this exotic component is the areas of high-surficial radioactivity observed by orbital gamma ray spectrometry, such as those at Fra Mauro and Archimedes. If the exotic component is fine-grained KREEP, the origin and distribution of KREEP fragments in the soils are identified. It is suggested that the exotic component represents trace element enriched material located at some depth in the Imbrium area which was surficially deposited during Imbrium excavation.

Evensen, N. M.↗
NASA NTRS1972

Rubidium-strontium and potassium-argon age of lunar sample 15555.

The lunar mare basalt 15555 from the edge of Hadley Rille has been dated at 3.3 b.y. by both rubidium-strontium and potassium-argon techniques. Age and trace element abundances closely resemble those of the Apollo 12 mare basalts. Data from lunar basalts obtained thus far indicate that they cannot be derived by simple fractionation from a homogeneous source.

Murthy, V. R.↗
NASA NTRS1972

Apollo 14 and 15 samples - Rb-Sr ages, trace elements, and lunar evolution.

Studies concerning Rb-Sr isotopic relations are discussed together with abundance measurements regarding K, Rb, Sr, and Ba in Apollo 14 and 15 rocks and soils. The studies include age determination by the internal isochron technique on one basaltic rock sample from each of the two missions. In addition, total sample measurements have been made on samples of fines material from both missions. Trace element abundances and Rb-Sr systematics in the various grain size fractions of three of the fines have also been analyzed.

Murthy, V. R.↗