Aqueous Alteration on Mars Importance Some background Alteration products in Martian meteorites Martian origin for products Nature of products Experimental data Ages of weathering products Evidence from Viking, Pathfinder, and MER analyses Rates of weathering Jeff Taylor Aqueous Alteration on Mars

Importance of Understanding Aqueous Alteration on Mars Understand geologic environments at surface, including habitability Estimate duration of surface-water events Estimate conditions of groundwater-cryosphere system Date times of aqueous alterations Understand history of climate on Mars Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Definition: Change in chemical and/or mineralogical composition of rock in response to interactions with H2O-bearing ices, liquids, and vapors at ambient or hydrothermal (above ambient) temperatures. Chemical alteration takes place by hydrolysis, hydration, oxidation, carbonation, ion exchange (between crystals and solutions) Alteration without removal of elements is isochemical (closed system). Opposite is open system alteration Excellent general discussion can be found in Chapter 23 of The Martian Surface: Composition, Mineralogy, and Physical Properties (Jim Bell, editor). The chapter is by Doug Ming, Dick Morris, and Ben Clark. A good review about alteration products in Martian meteorites is: Bridges, J. C. et al. (2001) Alteration assemblages in Martian meteorites: Implications for Near-Surface Processes. Space Sci. Rev. 96, 365-392. Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Variables Initial rock mineralogy Anhydrous igneous minerals not stable at surface with water Temperature Water chemistry (e.g., no SO4-2, no sulfate forms) pH (H+ activity) Pressure Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Settings Weathering—Surfaces of Earth and Mars Hydrothermal alteration (> ~25C, ≥ 1 bar) Late-stage magmatic fluids Fumeroles (magmatic fluids and rain or groundwater) Burial Subduction Internal heating of rock/ice mixtures Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars pH, in case you forgot H2O H+ + OH- Kwater = mH+ + mOH- = 10-14 (dissociation constant of water) m = moles of solute/kg of water (Always some of both H+ and OH-) Can give acidity by conc of H+ alone: pH = -log(mH+), hence log of the activity of H+ Acidic, < 7 mH+ Neutral, 7 mH+ Alkaline (Basic), >7 Jeff Taylor Aqueous Alteration on Mars

Hydrolysis Definition: The breakup of a chemical bond using water. For example: Cl-(aq) NaCl Na+(aq) +Cl-(aq) Na+(aq) http://chemwiki.ucdavis.edu/Core/Physical_Chemistry/Equilibria/Solubilty/Hydrolysis Jeff Taylor

Hydrolysis of Silicates Mg2SiO4 + 4H2O 2Mg2+ + 4OH- +H4SiO4 Mg2SiO4 + 4H+ 2Mg2+ +H4SiO4 Fe2SiO4 + 4H+ 2Fe2+ + H4SiO4 The Fe2+, Mg2+ and other ions may not stay in solution: (Fe,Mg)2SiO4 +4H+ = Fe2+ + Mg2+ +H4SiO4 Fe3O4, Fe2O3 MgSO4 SiO2 (amorphous) FeO(OH) MgCl2 Silicious clays FeSO4 Mg3Si2O5(OH)4 Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Giant’s Causeway 30-meter thick soil layer 1-2 My time gap between lower and upper flows Jeff Taylor Aqueous Alteration on Mars

Giant’s Causeway Corestone Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Critical Zone According to a National Research Council report, the Earth's Critical Zone is the “heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air, and living organisms regulate the natural habitat and determine the availability of life-sustaining resources” (from http://en.wikipedia.org/wiki/Earth%27s_Critical_Zone). Critical zone: Heterogeneous, near surface environment that features complex interactions among rock, soil, water, air, and organisms. Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Weathering on Earth Jeff Taylor Aqueous Alteration on Mars

Terrestrial Mineral Evolution Increasing number of water-bearing minerals Hazen, R.M. and Ferry, J.M. (2010) Mineral evolution: Mineralogy in the fourth dimension. Elements 6, 9-12. DOI: 10.2113/gselements.6.1.9 Jeff Taylor Aqueous Alteration on Mars Hazen and Ferry (2010)

Mars Mineral Evolution Igneous rocks Olivine Pyroxenes Plagioclase Ilmenite Magnetite Apatite Jeff Taylor Aqueous Alteration on Mars

Common Alteration Minerals: Phyllosilicates (Clay Minerals) http://pubs.usgs.gov/of/2001/of01-041/htmldocs/clays/kaogr.htm Three-layer structure: Smectite: montmorillonite, (Na,Ca)(Al,Mg)2(Si4O10)•nH2O vermiculite, (Mg,Ca)(Mg,Fe3+,Al)3((Al,Si)4O10•H2O Two-layer structure Kaolinite, Al2Si2O5(OH)4 Jeff Taylor Aqueous Alteration on Mars

Common Alteration Minerals: Carbonates Note miscibility gaps, based on experiments Compositions in shaded areas not common and if present represent nonequilibrium conditions Jeff Taylor Aqueous Alteration on Mars

Common Alteration Minerals: Sulfates and Halides There are > 100 sulfate minerals Common in Mars Meteorites and inferred on surface: Anhydrite, CaSO4 Gypsum, CaSO4•2H2O Epsomite, MgSO4 •7H2O Kieserite, MgSO4·H2O Halides Halite, NaCl (rock salt) Sylvite, KCl Jeff Taylor Aqueous Alteration on Mars

Common Alteration Minerals: Zeolites At least 40 different minerals in zeolite group Framework silicates Tetrahedra of SiO4 and AlO4 linked to form channels, cages, rings, loops Form cage-like openings in structure Channels and cages permit cations and H2O to pass in and out Result: can be used as molecular sieves in water softeners, or as kitty litter Typically form as secondary minerals in cracks or cavities in mafic igneous rocks Examples: Natrolite,Na2Al2Si3O10 •2H2O Chabazite, CaAl2Si4O12 •6H2O Heulandite, CaAl2Si7O18 •7H2O Stilbite, CaAl2Si7O18 •7H2O Jeff Taylor Aqueous Alteration on Mars

Common Alteration Minerals: Iron Oxides and Hydroxides Hematite, Fe2O3 Magnetite, Fe3O4 Goethite, FeO(OH) Lepidocrocite is a polymorph Limonite is fine-grained geothite Ferrihydrite, Fe2O3 •0.5 H2O Nanophase iron oxide Jeff Taylor Aqueous Alteration on Mars

Common Alteration Minerals: Iddingsite Rusty red stuff that forms veinlets Common alteration product Mixture of Fe-bearing smectite and iron oxides (ferrihydrite and magnetite) Smectite usually poorly crystalline Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration in SNC Meteorites Fusion crust cuts across alteration Best evidence for extraterrestrial origin Jeff Taylor Aqueous Alteration on Mars

Evidence for Martian Origin Pre-terrestrial fracturing D/H in some phases too high to be terrrestrial, but consistent with high D/H in Martian atmosphere Phases with C, O, and S isotopes inconsistent with terrestrial alteration Ages far older (> 600 My) than terrestrial residence times However, except for ALH84001 and the nakhlites, others have not been as well documented Jeff Taylor Aqueous Alteration on Mars

Summary of Alteration Phases in Nakhlites Lafayette: Ca-rich siderite, smectite, gypsum Governador Valadares: Smectite, siderite, gypsum Nakhla: Smectite, siderite, gypsum, anhydrite, halite, epsomite, goethite These form an evaporation sequence from a brine (Bridges and Grady, 2000): Lafayette, 25% brine remaining Governador Valadares, 20% brine remaining Nakhla, 10% brine remaining Bridges, J. C. and Grady, M. M.(2000) Evaporite mineral assemblages in the Nakhlite (Martian) meteorites. Earth Planet. Sci. Lett. 176, 267-279. Jeff Taylor Aqueous Alteration on Mars

Alteration in Nakhlites 50 microns Halite (h), anhydrite (a), and siderite (sd) in Nakhla Iddingsite in Lafayette; sd is Siderite, sm is smectite Jeff Taylor Aqueous Alteration on Mars

Alteration in Chassigny Occurs in veins in olivine; probably deposited from brines Calcite Magnesite Gypsum Not an alteration product: Amphibole (kaersutite) in melt inclusions Shows there was water in magma Jeff Taylor Aqueous Alteration on Mars

Alteration in Shergottites Have to worry about effects of shock on alteration phases—can convert low-T products to higher-T products No systematic study of alterations and shock has been done Alterations described only from Shergotty and EET 79001: Calcite Gypsum Sulfates Phyllosilicates (Shergotty) Jeff Taylor Aqueous Alteration on Mars

Aqueous Alteration on Mars Alteration in ALH 84001 Carbonates in ALH84001 form disks with compositions varying continuously among carbonate endmembers (gray field) On the diagram, Lafayette points are crosses, GV are triangles, Nakhla is circles Important point: some carbonate on Mars Jeff Taylor Aqueous Alteration on Mars