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Processes involved in the formation of magnesian-suite plutonic rocks from the highlands of the Earth's MoonThe earliest evolution of the Moon likely included the formation of a magma ocean and the subsequent development of anorthositic flotation cumulates. This primary anorthositic crust was then intruded by mafic magmas which crystallized to form the lunar highlands magnesian suite. The present study is a compilation of petrologic, mineral-chemical, and geochemical information on all pristine magnesian-suite plutonic rocks and the interpretation of this data in light of 18 'new' samples. Of these 18 clasts taken from Apollo 14 breccias, 12 are probably pristine and include four dunites, two norites, four troctolites, and two anorthosites. Radiogenic isotopic whole rock data also are reported for one of the 'probably pristine' anorthositic troctolites, sample 14303,347. The relatively low Rb content and high Sm and Nd abundances of 14303,347 suggest that this cumulate rock was derived from a parental magma which had these chemical characteristics. Trace element, isotopic, and mineral-chemical data are used to interpret the total highlands magnesian suite as crustal precipitates of a primitive KREEP (possessing a K-, rare earth element (REE)-, and P-enriched chemical signature) basalt magma. This KREEP basalt was created by the mixing of ascending ultramafic melts from the lunar interior with urKREEP (the late, K-, REE-, and P-enriched residuum of the lunar magma ocean). A few samples of the magnesian suite with extremely elevated large-ion lithophile elements (5-10x other magnesian-suite rocks) cannot be explained by this model or any other model of autometasomatism, equilibrium crystallization, or 'local melt-pocket equilibrium' without recourse to an extremely large-ion lithophile element-enriched parent liquid. It is difficult to generate parental liquids which are 2-4 x higher in the REE than average lunar KREEP, unless the liquids are the basic complement of a liquid-liquid pair, i.e., the so-called 'REEP-fraction,' from the silicate liquid immiscibility of urKREEP. Scarce age information on lunar rocks suggests that magnesian-suite magmatism was initiated at progressively more recent time from the northeast to the southwest on the lunar nearside from 4.45 to 4.25 Ga.
Document ID
19950059123
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Snyder, Gregory A.
(University of Tennessee, Knoxville, TN United States)
Neal, Clive R.
(University of Tennessee, Knoxville, TN United States)
Taylor, Lawrence A.
(University of Tennessee, Knoxville, TN United States)
Halliday, Alex N.
(University of Michigan, Ann Arbor, MI United States)
Date Acquired
August 16, 2013
Publication Date
May 25, 1995
Publication Information
Publication: Journal of Geophysical Research
Volume: 100
Issue: E5
ISSN: 0148-0227
Subject Category
Lunar And Planetary Exploration
Accession Number
95A90722
Funding Number(s)
CONTRACT_GRANT: NSF 90-14877
CONTRACT_GRANT: NAG9-62
CONTRACT_GRANT: NSF 90-04133
CONTRACT_GRANT: NAG9-415
Distribution Limits
Public
Copyright
Other

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