Mathematics – Logic
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002usnc.conf...33l&link_type=abstract
Unmixing the SNCs: Chemical, Isotopic, and Petrologic Components of the Martian Meteorites, p. 33-34
Mathematics
Logic
Crystallization, Snc Meteorites, Meteoritic Composition, Mars (Planet), Planetary Mantles, Basalt, Shergottites, Aluminum Oxides, Antarctic Regions, Melting, Achondrites
Scientific paper
Detailed chemical and isotopic measurements reveal complexities in planetary differentiation that will make any reconstruction of the SNC source region difficult. Recent age determinations of shergottites have resolved a long-standing uncertainty in their crystallization ages in favor of ages in the range of 200 to 400 Ma. These young ages, together with 1.3 Ga ages of the Nahklites and Chassigny, require that the SNC source regions maintained more pronounced depletions of incompatible elements than the terrestrial MORB source since primordial differentiation (4.525 Ga) and that the parent magmas of the classical shergottites (Shergotty, Zagami) assimilated a long term light-REE enriched component (crust). The isotopic evidence indicates little or no mixing between differentiated and primitive mantle or between differentiated mantle and crust during martian history. Estimated SNC parent magma compositions have lower Al2O3 concentrations than terrestrial MORB and OIB. These low Al2O3 contents are consistent with highly depleted source regions as inferred from the isotopic data. New modeling of polybaric melting reveals that the extent of the depletion in terms of major elements is greater than expected for basalt extraction. There are two general scenarios consistent with the major elements: one is that the portion of the martian mantle from which the SNC magmas are derived is a magma ocean cumulate; the other is that initial melts in a polybaric fractional fusion event were never aggregated with later melts (possibly the inial melts were too dense). Loss of the initial melts is also consistent with the extremely high Sm/Nd ratios inferred for the parent magmas of the Antarctic shergottites.
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