TY - JOUR
T1 - Aqueous alteration of the Martian meteorite Northwest Africa 817: Probing fluid?rock interaction at the nakhlite launch site
AU - Lee, M.R.
AU - Daly, L.
AU - Cohen, B.E.
AU - Hallis, L.J.
AU - Griffin, S.
AU - Trimby, P.
AU - Boyce, A.
AU - Mark, D.F.
N1 - This work was funded by the Science and Technology Facilities Council through grants ST/N000846/1 and ST/H002960/1.
Author was at University of Glasgow when this was accepted and published, Glasgow complied with OA. See link.
PY - 2019/11/1
Y1 - 2019/11/1
N2 - The nakhlite meteorites characteristically contain iddingsite, a hydrous iron?magnesium silicate that formed by aqueous alteration on Mars. Iddingsite is most abundant in Northwest Africa (NWA) 817, and alteration products in this meteorite also have the lowest deuterium/hydrogen ratio of any nakhlite. Taken together, these distinctive properties could be interpreted to show that NWA 817 was altered under different physico?chemical conditions than the other nakhlites and by liquid water from a separate reservoir. Here this interpretation is tested through a petrographic, mineralogical, chemical, and isotopic study of NWA 817. We find that its iddingsite occurs as olivine?hosted veins of nanocrystalline smectite and Fe?oxyhydroxide. Strong similarities in the mineralogy of iddingsite between NWA 817 and other nakhlites suggest that these meteorites were altered under comparable physico?chemical conditions, with the Fe?rich composition of NWA 817 olivine grains rendering them especially susceptible to aqueous alteration. Analyses of NWA 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium/hydrogen ratios, but owing to terrestrial weathering of this meteorite, the hydrogen isotopic data cannot be used with confidence to infer the origin of Martian aqueous solutions. NWA 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system. One interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of Mars and flowed through the nakhlite lava pile under the influence of gravity.
AB - The nakhlite meteorites characteristically contain iddingsite, a hydrous iron?magnesium silicate that formed by aqueous alteration on Mars. Iddingsite is most abundant in Northwest Africa (NWA) 817, and alteration products in this meteorite also have the lowest deuterium/hydrogen ratio of any nakhlite. Taken together, these distinctive properties could be interpreted to show that NWA 817 was altered under different physico?chemical conditions than the other nakhlites and by liquid water from a separate reservoir. Here this interpretation is tested through a petrographic, mineralogical, chemical, and isotopic study of NWA 817. We find that its iddingsite occurs as olivine?hosted veins of nanocrystalline smectite and Fe?oxyhydroxide. Strong similarities in the mineralogy of iddingsite between NWA 817 and other nakhlites suggest that these meteorites were altered under comparable physico?chemical conditions, with the Fe?rich composition of NWA 817 olivine grains rendering them especially susceptible to aqueous alteration. Analyses of NWA 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium/hydrogen ratios, but owing to terrestrial weathering of this meteorite, the hydrogen isotopic data cannot be used with confidence to infer the origin of Martian aqueous solutions. NWA 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system. One interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of Mars and flowed through the nakhlite lava pile under the influence of gravity.
U2 - 10.1111/maps.13136
DO - 10.1111/maps.13136
M3 - Article
SN - 1086-9379
VL - 53
SP - 2395
EP - 2412
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
IS - 11
ER -