R. K. L. Lum

Rb, Sr and strontium isotopic composition, K/Ar age and large ion lithophile trace element abundances in rocks and glasses from the Wanapitei Lake impact structure

Abstract Shock metamorphosed rocks and shock-produced melt glasses from the Wanapitei Lake impact structure have been examined petrographically and by electron microprobe. Eleven clasts exhibiting varying degrees of shock metamorphism and eight impact-produced glasses have been analyzed for Rb, Sr and Sr isotopic composition. Five clasts and one glass have also been analyzed for large ion lithophile (LIL) trace element abundances including Li, Rb, Sr, and Ba and the REEs. The impact event forming the Wanapitei Lake structure occurred 37 m.y. ago based on K/Ar dating of glass and glassy whole-rock samples. Rb/Sr isotopic dating failed to provide a meaningful whole-rock or internal isochron. The isotopic composition of the glasses can be explained by impact-produced mixing and melting of metasediments. Large ion lithophile trace element abundance patterns confirm the origin of the glasses by total shock melting of metasediments.

Major, minor and trace element abundances in samples from the Apollo 17 station 7 boulder - Implications for the origin of early lunar crustal rocks

Abstract Apollo 17 station 7 boulder consortia samples were analyzed for major and minor elements by a combined semimicro atomic absorption spectrophotometric and colorimetric procedure. Lithophile trace element abundances were determined by stable isotope dilution mass spectrometry. Three matrix types samples (77135, 77115, and 77075) were found to be KREEP-rich fragment-laden melts with analogues throughout the Apollo 17 landing site. Of the five clasts analyzed, at least one (77115,19, troctolite) is thought to be a cumulate; 77135, 77115, and 77075 are thought to have originated by impact fusion of material with similar composition. This original material may represent a partial melt of a parent material of the composition of an included, shocked norite breccia (77215).

Luna 20 and Apollo 16 core fines: large-ion lithophile trace-element abundances

Abstract Li, K, Rb and Sr abundances have been determined by mass-spectrometric stable isotope dilution analysis for a sample of Luna 20 fines and for eight fines from the Apollo 16 deep drill core. Ba and rare-earth abundances have also been determined for the Luna 20 sample and two of the Apollo 16 samples. Luna 20 and Apollo 16 were the first missions to interior highlands sites. The trace-element similarity of the fines samples may indicate that the lunar highlands are fairly homogeneous. An abundant feldspathic component is indicated. However, the negative Eu anomalies indicate that the fines cannot have been made entirely from earthly feldspathic cumulates. As in the case of the Apollo 12 and 15 core samples, the abundance of the large-ion lithophile trace elements increases with depth in the Apollo 16 core. It is suggested that Apollo 16 core material was lost during separation of the drill sections on the Moon.