Mathematics – Logic
Scientific paper
Jan 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986jgr....91..e84s&link_type=abstract
Journal of Geophysical Research, Volume 91, Issue B13, p. E84-E90
Mathematics
Logic
Scientific paper
We utilize a variety of lunar sample and orbital geochemical data in conjunction with current knowledge of impact-cratering processes to develop a chemical and petrological model of the lunar crust. Orbital chemical data indicate that the upper highlands surface on the moon has the bulk composition of ``anorthositic gabbro'' (Al2O3 26-28 wt%) greater than 90% of the area covered is dominated by material having compositional affinities with the ferroan anorthosites, rather than with Apollo-type Mg-suite rocks. Considerations of the cumulative bombardment history of the moon indicate that the outer zone of impact brecciation extends tens of kilometers into the crust; given the resolution of the orbital gamma ray data, the ferroan-anorthositic composition derived for the highlands surface may represent the bulk composition of the upper half of the lunar crust. The observed enrichment in ``noritic'' components in basin ejecta with increasing basin size, together with considerations of impact melt petrogenesis in lunar basins, suggest that the bulk composition of the lower lunar crust is ``noritic'' (Al2O3~20 wt%) samples of lower crustal material are probably present in the Apollo collections in the form of low-K Fra Mauro (LKFM) and very high alumina (VHA) basaltic impact melts. Our estimated value of total crustal Al2O3 content (24-25 wt%) suggests that the lunar crust contains too much aluminum to have originated by a purely ``serial magmatism'' mechanism. The large abundance of plagioclase within the lunar crust is probably a result of global-scale fractionation of plagioclase in early lunar history. The ``magma ocean'' hypothesis of crustal origin more readily explains the bulk composition of the lunar crust.
Davis Philip A.
Spudis Paul D.
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