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Descartes Mountains and Cayley Plains - Composition and provenanceTrace element compositions of petrographically characterized 2-4 mm lithic fragments from Apollo 16 soil samples are used to calculate initial REE concentrations in liquids in equilibrium with lunar anorthosites and to discuss the provenance of the Cayley Formation. Lithic fragments may be subdivided into four groups: (1) ANT rocks, (2) K- and SiO2-rich mesostasis-bearing rocks, (3) poikiloblastic rocks, and (4) (spinel) troctolites. Model liquids in equilibrium with essentially monominerallic anorthosites have initial REE concentrations 5-8 times those of chondrites. The REE contents of K- and SiO2-rich mesostasis-bearing rocks and poikiloblastic rocks are dominated by the mesostasis phases. ANT rocks appear to be more abundant in the Descartes Mountains, while poikiloblastic rocks appear to be more abundant in the Cayley Plains. Poikiloblastic rocks have intermediate to high LIL-element concentrations yet the low gamma-ray activity of Mare Orientale implies low LIL-element concentrations. Consequently, it is unlikely that the Cayley Formation is Orientale ejecta. A local origin as ejecta from smaller impacts is a more plausible model for the deposition of the Cayley Formation.
Document ID
19750055532
Document Type
Conference Proceedings
Authors
Drake, M. J.
Taylor, G. J. (Smithsonian Astrophysical Observatory Cambridge, Mass., United States)
Goles, G. G. (Oregon, University Eugene, Ore., United States)
Date Acquired
August 8, 2013
Publication Date
January 1, 1974
Subject Category
LUNAR AND PLANETARY EXPLORATION
Meeting Information
Lunar Science Conference(Houston, TX)
Funding Number(s)
CONTRACT_GRANT: NGL-09-015-150
CONTRACT_GRANT: NGL-38-003-024
Distribution Limits
Public
Copyright
Other