Jd. Gleason et al., PETROGRAPHY AND BULK CHEMISTRY OF MARTIAN ORTHOPYROXENITE ALH84001 - IMPLICATIONS FOR THE ORIGIN OF SECONDARY CARBONATES, Geochimica et cosmochimica acta, 61(16), 1997, pp. 3503-3512
New petrologic and bulk geochemical data for the SNC-related (Martian)
meteorite ALH84001 suggest a relatively simple igneous history overpr
inted by complex shock and hydrothermal processes. ALH84001 is an igne
ous orthopyroxene cumulate containing penetrative shock deformation te
xtures and a few percent secondary extraterrestrial carbonates. Rare e
arth element (REE) patterns for several splits of the meteorite reveal
substantial heterogeneity in REE abundances and significant fractiona
tion of the REEs between crushed and uncrushed domains within the mete
orite. Complex zoning in carbonates indicates nonequilibrium processes
were involved in their formation, suggesting that CO2 rich fluids of
variable composition infiltrated the rock while on Mars. We interpret
petrographic textures to be consistent with an inorganic origin for th
e carbonate involving dissolution-replacement reactions between CO2-ch
arged fluids and feldspathic glass in the meteorite. Carbonate formati
on clearly post dated processes that last redistributed the REE in the
meteorite. (C) 1997 Elsevier Science Ltd.