Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p14a..09r&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P14A-09
Physics
[1026] Geochemistry / Composition Of The Moon, [3630] Mineralogy And Petrology / Experimental Mineralogy And Petrology, [3672] Mineralogy And Petrology / Planetary Mineralogy And Petrology, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
The current paradigm for solidification of the Moon after condensation is that of the crystallization and differentiation of a Lunar Magma Ocean (LMO)[1]. In this model, the crystallization of the LMO gave rise to the plagioclase-rich ferroan anorthosite highlands crust, due to flotation of less dense plagioclase in the mafic magma ocean; and to mafic cumulates rich in olivine and pyroxene, which were later re-melted due to gravitational instability and mantle overturn to produce basaltic magmas such as mare basalts and picritic pyroclastic glasses. LMO crystallization also produced KREEP, which is thought to have later hybridized with the ascending basaltic magmas resulting in specific minor and trace element enrichments in seen in lunar basalts. KREEP is thought to represent the very last liquids in the magma ocean crystallization sequence, in which incompatible elements are concentrated. Numerical simulations have been used to determine the crystallization sequence of the LMO, the extent of fractional crystallization versus bulk crystallization[2], and the density profile of the resultant cumulate pile[3]. However these models, on which a large portion of lunar research is predicated, remain largely untested experimentally. The Snyder model[2] features crystal suspension in the magma ocean due to vigorous convection, and equilibrium crystallization for the majority of LMO crystallization followed by fractional crystallization of the residual magma ocean. This model has been tested experimentally[4], and found to produce a different cumulate assemblage from that predicted by Snyder. We are experimentally simulating fractional crystallization of the LMO from the outset of LMO solidification, as an alternate end-member model of lunar differentiation. We find that fractional crystallization of the lower portion of the LMO produces a divergence of residual liquid compositions from that of the equilibrium crystallization process (somewhat more orthopyroxene-normative). These differences are likely to be more pronounced as fractional crystallization proceeds, leading to concomitant differences in crystallizing assemblages including a lack of garnet in the lunar interior, which has implications for the potential thickness of the anorthosite crust. [1] Wieczorek et. al; Shearer et. al. (2006) Rev. Mineral. and Geochem. 60. [2] Snyder et. al. (1992) Geochim. Cosmochim. Acta 56, 3809-3823. [3] Elkins-Tanton et. al. (2002) Earth Planet. Sci. Lett. 196, 239-249[4] Elardo et. al. (2011) Geochimica et Cosmochimica Acta 75:3024-3045
Draper David S.
Rapp Jennifer F.
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