Formation of iddingsite veins in the martian crust by centripetal replacement of olivine: Evidence from the nakhlite meteorite Lafayette

Abstract

The Lafayette meteorite is an olivine clinopyroxenite that crystallized on Mars $1300 million years ago within a lava flow or shallow sill. Liquid water entered this igneous rock $700 million years later to produce a suite of secondary minerals, collectively called 'iddingsite', that occur as veins within grains of augite and olivine. The deuterium/hydrogen ratio of water within these secondary minerals shows that the aqueous solutions were sourced from one or more near-surface reservoirs. Several petrographically distinct types of veins can be recognised by differences in their width, shape, and crystallographic orientation. Augite and olivine both contain veins of a very fine grained hydrous Fe-and Mg-rich silicate that are $1-2 lm in width and lack any preferred crystallographic orientation. These narrow veins formed by cementation of pore spaces that had been opened by fracturing and probably in response to shock. The subset of olivine-hosted veins whose axes lie parallel to (0 0 1) have serrated walls, and formed by widening of the narrow veins by interface coupled dissolution-precipitation. Widening started by replacement of the walls of the narrow precursor veins by Fe-Mg silicate, and a crystallographic control on the trajectory of the dissolution-precipitation front created micrometre-scale {1 1 1} serrations. The walls of many of the finely serrated veins were subsequently replaced by siderite, and the solutions responsible for carbonation of olivine also partially recrystallized the Fe-Mg silicate. Smectite was the last mineral to form and grew by replacement of siderite. This mineralization sequence shows that Lafayette was exposed to two discrete pulses of aqueous solutions, the first of which formed the Fe-Mg silicate, and the second mediated replacement of vein walls by siderite and smectite. The similarity in size, shape and crystallographic orientation of iddingsite veins in the Lafayette meteorite and in terrestrial basalts demonstrates a common microstructural control on water-mineral interaction between Mars and Earth, and indicates that prior shock deformation was not a prerequisite for aqueous alteration of the martian crust.

Opal‐A in the Nakhla meteorite: A tracer of ephemeral liquid water in the Amazonian crust of Mars

“…; Lee et al. ), these solutions were likely to have been present widely throughout the lava flow/sill. The initial fluids are interpreted to have been acidic (pH<~4) and oxidizing; they dissolved olivine and precipitated opal‐A and ferrihydrite.…”

“…We have found that the Nakhla iddingsite veins contain evidence for the former presence of several generations of aqueous solutions that had a distinctly different pH, Eh, and solute composition, although water/rock ratios are likely to have been uniformly low. The high D/H values of Fe-Mg silicate and siderite suggests that these components had formed from solutions of a similar derivation (i.e., that had equilibrated with the H-depleted Martian atmosphere), and as Fe-Mg silicate and siderite also occur together within veins from the Lafayette nakhlite Lee et al 2015), these solutions were likely to have been present widely throughout the lava flow/ sill. The initial fluids are interpreted to have been acidic (pH<~4) and oxidizing; they dissolved olivine and precipitated opal-A and ferrihydrite.…”

“…The nakhlites are cumulate clinopyroxenites, most of which are olivine-bearing, and contain the greatest volume and diversity of waterformed minerals among the Martian meteorites. Collectively called "iddingsite," these minerals include phyllosilicates, carbonates, sulfates, and halides (e.g., Bunch and Reid 1975;Reid and Bunch 1975;Gooding et al 1991;Treiman et al 1993;Bridges and Grady 2000;Noguchi et al 2009;Changela and Bridges 2011;Lee et al 2013Lee et al , 2015Tomkinson et al 2013Tomkinson et al , 2015. A preterrestrial (i.e., Martian) origin for the iddingsite is demonstrated by the fact that it is cut by the meteorite fusion crust , and samples from the Lafayette and Yamato-000593 meteorites yield a radiometric formation age of 633 AE 23 Ma (i.e., Amazonian: Borg and Drake 2005).…”

Replacement of glass in the Nakhla meteorite by berthierine: Implications for understanding the origins of aluminum‐rich phyllosilicates on Mars

“…; Lee et al. ), thus indicating that physico‐chemical conditions were similar within the nakhlite parent rock(s).…”

57Fe Mössbauer, XRD, FT-IR, FE SEM Analyses of Natural Goethite, Hematite and Siderite

“…[31][32][33][34][35] After landing the Mössbauer instrumentation along with other spectroscopic and imaging techniques on the Mars surface the presence of goethite and jarosite minerals was detected. This can be taken as strong evidence of water presence in far history of Mars.…”