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Effects of fractional crystallization and cumulus processes on mineral composition trends of some lunar and terrestrial rock seriesA plot of Mg of mafic minerals versus An of plagioclase in cumulate rocks from various lunar and terrestrial rock series shows each series to have a distinct curvilinear trend. The slopes of these trends vary from nearly vertical in the case of lunar anorthosites and Mg-norites to nearly horizontal in the case of gabbros from the mid-Atlantic ridge. Calculations based upon known major element partitioning between mafic minerals, plagioclase and subalkaline basaltic liquids indicate that fractional crystallization coupled with cotectic accumulation of mafic minerals and plagioclase will produce mineral composition trends on the Mg versus An diagram with slopes greater than 1 for cases where An is approximately greater than Mg. Furthermore, fractional crystallization of basaltic magmas with alkali concentrations approaching zero will produce near vertical Mg versus An trends. Therefore, the steep slopes of the lunar rock series are consistent with relatively simple fractionation processes. The relatively flat slope of mineral compositions from gabbros collected from the mid-Atlantic ridge at 26 deg N is inconsistent with simple fractionation processes, and calculations show that periodic refilling of a fractionating magma chamber with picritic magma cannot simply explain this flat slope either.
Document ID
19830034114
Acquisition Source
Legacy CDMS
Document Type
Conference Proceedings
Authors
Longhi, J.
(Yale University New Haven, CT, United States)
Date Acquired
August 11, 2013
Publication Date
January 1, 1982
Subject Category
Lunar And Planetary Exploration
Meeting Information
Meeting: Lunar and Planetary Science Conference
Location: Houston, TX
Start Date: March 15, 1982
End Date: March 19, 1982
Accession Number
83A15332
Funding Number(s)
CONTRACT_GRANT: NAGW-175
Distribution Limits
Public
Copyright
Other

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