Abstract
Veins containing carbonates, hydrous silicates, and sulfates that occur
within and between grains of augite and olivine in the Nakhla meteorite
are good evidence for the former presence of liquid water in the Martian
crust. Aqueous solutions gained access to grain interiors via narrow
fractures, and those fractures within olivine whose walls were oriented
close to (001) were preferentially widened by etching along [001]. This
orientation selective dissolution may have been due to the presence
within olivine of shock-formed [001](100) and [001]{110} screw
dislocations. The duration of etching is likely to have been brief,
possibly less than a year, and the solutions responsible were
sufficiently cool and reducing that laihunite did not form and Fe
liberated from the olivine was not immediately oxidized. The pores
within olivine were mineralized in sequence by siderite, nanocrystalline
smectite, a Fe-Mg phyllosilicate, and then gypsum, whereas only the
smectite occurs within augite. The nanocrystalline smectite was
deposited as submicrometer thick layers on etched vein walls, and
solution compositions varied substantially between and sometimes during
precipitation of each layer. Together with microcrystalline gypsum the
Fe-Mg phyllosilicate crystallized as water briefly returned to some of
the veins following desiccation fracturing of the smectite. These
results show that etching of olivine enhanced the porosity and
permeability of the nakhlite parent rock and that dissolution and
secondary mineralization took place within the same near-static aqueous
system.
Original language | English |
---|---|
Pages (from-to) | 224-240 |
Number of pages | 17 |
Journal | Meteoritics and Planetary Science |
Volume | 48 |
Issue number | 2 |
Early online date | 28 Jan 2013 |
DOIs | |
Publication status | Published - Feb 2013 |