IGCP-SIDA 599 Project Launching Meeting Mekrijärvi 2011

Modern weathering crust derived from the serpentinite substratum, BC, Canada Weathering crusts form as a result of long-term interactions with rain- or seawater at low temperature and pressure. As a consequence they are characterized by incompleteness of the chemical reactions passing. WEATHERING CRUSTS Introduction The thermodynamic calculations with accounting of minerals dissolution were implemented with the use of the program complex GEOCHEQ [Mironenko et al., 2008].

CARBONE DIOXIDE OR METHANE? CO 2 CH 4 1.Absence of the early Earth’s carbonate rock’s remnants [Shaw, 2008] 2.Inconvenience of none-highly reduced conditions for origin of life [e.g. Natochin et al., 2008] 1.Carbonate minerals (dolomite) described in the Isua sediments (3.8 Ga) [Myers, 2001] 2.The methane atmosphere could be provided in the case of a very low oxygen fugacity of upper mantle (less than bar) [Holland, 1984] Liquid water might exist on the early Earth’s surface as early as 4.4 Ga [e.g. Mojzsis et al., 2001; Cavosie et al., 2005; Watson and Harrison, 2005]. Thus, according to the faint young Sun paradox, a greenhouse gas is necessary OR Introduction

THE MODELING PARAMETERS (t, W/R, T, P) t – the general weathering duration (n – the quantity of solution waves, ΣΔt τ – the duration of one solution wave percolation) W/R – the ration of one water portion to the weathered rock weight Т and Р correspond to the conditions on the weathered substratum surface if ΣΔt τ = 1 day, a quantity of precipitation is 1000 mm/year, and a weathering crust thickness is 1 m, W/R would be with THE WEATHERING CRUST FORMING MODELING SCHEME The method description

THE CALCULATION PROCEDURE Primary minerals Secondary minerals [System composition] (t+t) = [Solution composition] t + Δ tΣ(Rate i S i ) Aqueous solution The kinetic control dissolution The thermodynamic control sedimentation The calculation of chemical equilibrium Dissolved matter during Δ t [Zolotov and Mironenko, 2007]

Rate = f 1 °(pH)·f 2 (T-T 0 )·f 3 (ΔG/RT) = Δt  Σ(Rate i  S i ) [Zolotov and Mironenko, 2007] The Arrhenius equation [Xu et al., 1999 ] The Lasaga equation [Lasaga, 1981] The method description THE MINERAL’S DISSOLUTION RATE EQUATION The Laidler empirical equation [Laidler, 1987]

THE INFLUENCE OF DIFFERENT FACTORS TO THE OLIVINE DISSOLUTION RATE [Olsen, 2007] The method description

THE REACTIONARY SURFACE SEM microphotographs illustrate the olivine dissolution [Lazaro and Brouwers, 2010] Δt  Σ(Rate i  S i ) S i = ν i  SSA, ν i – the volume portion of mineral j The specific surface area (SSA) of the most rocks is m 2 /g [Brantley et al, 1999]. The method description Index and type of samples Weight, g Observed surface, m 2 /g 6005 granite ± basalt ± granite ± Кс-1 clay ± 2.06

THE EXPERIMENTAL AND CALCULATED DATA The quartz dissolution at 23°С and atmospheric pressure SSA quartz = – m 2 /g [Worley, 1994] Time, days

THE CALCULATION RESULTS AS AGAINST THE EXPERIMENTAL DATA. THE SOLUTIONS COMPOSITION

THE MODELING SYSTEM The method description The modeled system: O-H-K-Mg-Ca-Al-C-Si-Na-Fe. As an analog of the early Earth’s protocrust we used the next basaltic komatiite compound from the Archean greenstone belt Munro Township (Canada) [Arndt, Nesbitt, 1982], wt. %: SiO 2 = 48.76, Al = 9.36, Fe 2 O 3 = 3.07, FeO = 8.04, MgO =21.65, CaO = 8.05, Na 2 O = 0.90, К 2 O = We used kinetic constants for the next minerals: albite, amorphous silica, brucite, calcite, chrysotile, clinochlore, daphnite, diopside, dolomite, enstitite, fayalite, ferrosilite, forsterite, goethite, greenalite (Fe- serpentine), illite, magnesite, magnetite, Ca, K, Na,Fe-montmorillonites, siderite, talc. Temperature was 15°С and pressure 1 bar. The system was open by CO 2 or CH 4.

Results of calculations THE WEATHERING CRUST The CO 2 atmosphere (P CO2 = 1 bar) The primary minerals dissolution sequence: Opx (32 model years)  Ol, Cpx (54)  Mag (60)  Pl (1900). The resulted weathering crust consisted from amorphous silica (61.8 vol. %), Fe- montmorillonite (nontronite) (35.3 vol. %), goethite (2.8 vol. %) and illite (0.06 vol. %).

Initial composition 58 model years 100 model years 800 model years model years SiO 2 Al 2 O 3 FeO K 2 O CaO MgO Na 2 O СO 2 H 2 O V/V initial *100% Results of calculations THE BULK COMPOSITION OF WEATHERING CRUST The CO 2 containing atmosphere (P CO2 = 1 bar) The resulted weathering crust lost Mg, Ca, Na, and on the final stage Fe and K. It accumulated Si and Al.

Results of calculations THE WEATHERING CRUST The CH 4 atmosphere (P CH4 = 1 bar) The primary minerals dissolution sequence: Opx (0.3 model years)  Cpx (100)  Mag (615)  Ol (5200)  Pl (6000). The resulted weathering crust consisted from amorphous deweylite (58 vol. %) and chlorite (42 vol. %).

Initial composition 17 model years 68 model years 1200 model years model years SiO 2 Al 2 O 3 FeO K 2 O CaO MgO Na 2 O CO 2 H 2 O V/V initial *100% Results of calculations THE BULK COMPOSITION OF WEATHERING CRUST The CH 4 containing atmosphere (P CH4 = 1 bar) The resulted weathering crust lost Na, K and Ca. It accumulated Si, Fe, Al and Mg.

Discussion DISCUSSION

Conclusions CONCLUSIONS The carbonate minerals deposit effectively at the CO 2 atmosphere. Carbonates are the most stable at low quantity of atmospheric precipitates. During the consecutive weathering crust evolution they can be dissolved completely and removed from the substratum. The weathering crust formed at the CO 2 atmosphere conditions consists from amorphous silica, iron oxides and clay minerals. At the CH 4 atmosphere conditions – from deweylite and chlorite. The methane presence in the carbon dioxide atmosphere (CO 2 /CH 4 >1) doesn’t influence on the weathering crust composition. A developed weathering crust may be formed during first thousand years. We thank M.V. Mironenko (Vernadsky Institute) for providing programs and consultations. This investigation was financially supported by program no. 25 of the Presidium of the Russian Academy of Sciences, subprogram 1, theme "Reconstruction of the Formation Conditions of the Protocrust of the Early Earth and Its Role in the Evolution of the Composition of the Primary Atmosphere and Hydrosphere"

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