Ion and electron microprobe study of troctolites, norite, and anorthosites from Apollo 14: Evidence for urKREEP assimilation during petrogenesis of Apollo 14 Mg-suite rocks

Journal Article · Tue Sep 01 04:00:00 EDT 1998 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(98)00195-1· OSTI ID:329210

Shervais, J W; McGee, J J ^[1]

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1. Univ. of South Carolina, Columbia, SC (United States). Dept. of Geological Sciences

Most of the Moon`s highland crust comprises Fe-rich anorthosites with calcic plagioclase compositions. Subsequent evolution of the highland crust was dominated by troctolites, anorthosites, and norites of the Mg-suite. This plutonic series is characterized by calcic plagioclase, and mafic minerals with high mg{number_sign} (=100{sup *}Mg/[Mg + Fe]). In an effort to distinguish the origin of this important lunar rock series, the authors have analyzed the REE content of primary cumulus phases in ten Mg-suite cumulates using SIMS, along with their major and minor element compositions by electron microprobe analysis. Nine of these samples have high mg{number_sign}s, consistent with their formation from the most primitive parent melts of the Mg-suite. The data presented here show that Mg-suite troctolites and anorthosites preserve major and trace element characteristics acquired during their formation as igneous cumulate rocks and that these characteristics can be used to reconstruct related aspects of the parent magma composition. Data show that primitive cumulates of the Mg-suite crystallized from magmas with REE contents similar to high-K KREEP in both concentration and relative abundance. The highly enriched nature of this parent magma contrasts with its primitive major element characteristics, as pointed out by previous workers. This enigma is best explained by the mixing of residual magma ocean urKREEP melts with ultramagnesian komatiitic partial melts from the deep lunar interior. The data do not support earlier models that invoke crustal metasomatism to enrich the Mg-suite cumulates after formation, or models which call for a superKREEP parent for the troctolites and anorthosites.

• Sponsoring Organization: Sandia National Labs., Albuquerque, NM (United States)
• OSTI ID: 329210
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 17 Vol. 62; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ANORTHOSITES
APOLLO PROJECT
ELECTRON MICROPROBE ANALYSIS
ION MICROPROBE ANALYSIS
LUNAR MATERIALS
ORIGIN
PHOSPHORUS
PLUTONIC ROCKS
POTASSIUM
RARE EARTHS