Experimental and petrological constraints on lunar differentiation from the Apollo 15 green picritic glasses

Linda Elkins-Tanton, Nilanjan Chatterjee, Timothy L. Grove

Research output: Contribution to journalArticle

53 Citations (Scopus)

Abstract

Phase equilibrium experiments on the most magnesian Apollo 15C green picritic glass composition indicate a multiple saturation point with olivine and orthopyroxene at 1520°C and 1.3 GPa (about 260 km depth in the moon). This composition has the highest Mg# of any lunar picritic glass and the shallowest multiple saturation point. Experiments on an Apollo 15A composition indicate a multiple saturation point with olivine and orthopyroxene at 1520°C and 2.2 GPa (about 440 km depth in the moon). The importance of the distinctive compositional trends of the Apollo 15 groups A, B, and C picritic glasses merits the reanalysis of NASA slide 15426,72 with modern electron microprobe techniques. We confirm the compositional trends reported by Delano (1979, 1986) in the major element oxides SiO2, TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, and CaO, and we also obtained data for the trace elements P2O5, K2O, Na2O, NiO, S, Cu, Cl, Zn, and F. Petrogenetic modeling demonstrates that the Apollo 15 A-B-C glass trends could not have been formed by fractional crystallization or any continuous assimilation/fractional crystallization (AFC) process. The B and C glass compositional trends could not have been formed by batch or incremental melting of an olivine + orthopyroxene source or any other homogeneous source, though the A glasses may have been formed by congruent melting over a small pressure range at depth. The B compositional trend is well modeled by starting with an intermediate A composition and assimilating a shallower, melted cumulate, and the C compositional trend is well modeled by a second assimilation event. The assimilation process envisioned is one in which heat and mass transfer were separated in space and time. In an initial intrusive event, a picritic magma crystallized and provided heat to melt magma ocean cumulates. In a later replenishment event, the picritic magma incrementally mixed with the melted cumulate (creating the compositional trends in the green glass data set), ascended to the lunar surface, and erupted as a fire fountain. A barometer created from multiple saturation points provides a depth estimate of other glasses in the A-B-C trend and of the depths of assimilation. This barometer demonstrates that the Apollo 15 A-B-C trend originated over a depth range of ∼460 km to ∼260 km within the moon.

Original languageEnglish (US)
Pages (from-to)515-527
Number of pages13
JournalMeteoritics and Planetary Science
Volume38
Issue number4
StatePublished - Apr 2003
Externally publishedYes

Fingerprint

glass
trends
assimilation
natural satellites
cumulate
orthopyroxene
olivine
barometers
saturation
magma
Moon
fractional crystallization
melting
crystallization
trend
replenishment
lunar surface
phase equilibrium
chutes
trace elements

ASJC Scopus subject areas

  • Geophysics

Cite this

Experimental and petrological constraints on lunar differentiation from the Apollo 15 green picritic glasses. / Elkins-Tanton, Linda; Chatterjee, Nilanjan; Grove, Timothy L.

In: Meteoritics and Planetary Science, Vol. 38, No. 4, 04.2003, p. 515-527.

Research output: Contribution to journalArticle

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