Primitive SNC parent magmas and crystallization: Low PH2O experiments

Details Primitive SNC parent magmas and crystallization: Low PH2O experiments Primitive SNC parent magmas and crystallization: Low PH2O experiments

Mar 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24..503f&link_type=abstract

In Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F p 503-504 (SEE N94-12015 01-91)

Computer Science

1

Igneous Rocks, Magma, Mars Surface, Meteoritic Composition, Minerals, Planetary Composition, Water, Gas Composition, Melts (Crystal Growth), Petrology, Planetary Geology

Scientific paper

SNC meteorites are generally believed to present one of the best opportunities to study the composition and petrogenesis of Mars magmas. The crystallization ages, noble gas content, oxygen isotopic composition, and shocked minerals of the meteorites are consistent with a Martian origin. The samples range from dunite to clinopyroxenite to microgabbro. Efforts by researchers to determine parental magmas for the more primitive SNC meteorites have been complicated by crystal accumulation and possible melt segregation and removal. This has resulted in a range of parent magma estimates, although all appear to be Fe-rich and Al-poor. One major objective is to refine the Chassigny parent magma estimate by forcing olivine + clinopyroxene saturation upon the proposed melt composition. EETA 79001 magma compositions are also being investigated to determine the parent magma and the origin of the coarse-grained olivine and orthopyroxene megacrysts. Low pressure experiments with small but finite PH2O are being utilized to facilitate equilibrium, and to simulate the H2O indicated for these magmas. The presence of small (0.5-1.0 wt percent) amounts of H2O in SNC magmas appears to be required by the occurrence of hydrous minerals and textures in melts trapped by growing phenocrysts. This evidence for hydrous melts occurs in all SNC's except EETA 79001 and ALHA 77005, where the inclusion textures were obscured by shock effects. The lack of hydrous minerals or low temperature melts in the intercumulus regions of these rocks suggests that final emplacement was sufficiently close to the surface to allow degassing as the magma equilibrated with the low P atmosphere. Any H2O left in intercumulus phases would also tend to be lost during impact heating. Thus, although the bulk H2O of SNC's is very low, it is believed that this is explained by the near Mars surface emplacement of SNC magmas and by shock effects. Magmatic processes involving H2O need to be examined in order to characterize SNC magmas immediately prior to their final emplacement.

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