Halogen and argon evidence of Martian hydrous fluids in nakhlite meteorites Ray Burgess

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1 Halogen and argon evidence of Martian hydrous fluids in nakhlite meteorites Ray Burgess School of Earth, Atmospheric and Environmental Sciences University of Manchester, UK

2 Topics Halogens and noble gases Methods Halogens on Earth and Mars Nakhlite meteorites and samples Evidence for a fluid phase Summary

3 Halogen noble noble gas properties Volatile elements - highly depleted and low abundances in the Earth and Mars compared to solar values. Incompatible and conservative elements with similar ionic radii strongly partition in to the fluid and gas phases. low concentrations in minerals lattices. accumulate, no exchange (cf. H,O,S), Endmember fluid sources have unique and resolvable noble gas isotopic and halogen ratios that differ by orders of magnitude.

4 Key Information Fingerprinting the source of fluids, their modification and mixing processes. Physical processes diffusion, boiling, evaporation. Temperatures of recharge waters. Timing of aqueous fluid flow, residence ages. Fluid rock interaction isotope accummulation.

5 Methods 39 K(n,p) 39 Ar( - ) 39 K 40 Ca(n, ) 37 Ar ( - ) 37 Cl 37 Cl(n, ) 38 Cl( - ) 38 Ar 79 Br(n, ) 80 Br( - ) 80 Kr 127 I(n, ) 128 I( - ) 128 Xe Detection limits are between g Cl and gi Natural and neutron-derived noble gas isotopes are released from samples by crushing or heating using furnaces and lasers.

7 Halogens in surface reservoirs 72% Chlorine Continental sediments Continental crust 1% 1% 14% 12% Ocean sediments Ocean crust Seawater 76% Bromine 67% 7% 4% 4% 9% Iodine Br/Cl ~ I/Cl ~ % 1% 28% 1% Data from: Schilling et al. (1978); Muramatsu & Wedepohl (1998): Boneb et al. (1991)

8 Terrestrial halogens

9 Cl distribution ib i on Mars surface High Cl abundances wt% landers <4wt% Mars Odyssey Correlates with H abundance Enrichment mechanisms Aqueous Volcanic Aeolian Hydrothermal Keller et al JGR, 2007

10 Cl and Br martian surface Meridiani Planum (Opportunity) Rocks and soils similar Br/Cl >10x times CI value Br enrichment process unknown (evaporitic?) Martian meteorites Cl levels ppm Near chondritic Br/Cl Affects of terrestrial halogens? Reider et al Science, 2004

11 Cl-rich martian mantle Cl in place of water as dominant volatile species. Mars Cl-rich (2.5x) compared to the Earth. Cl and water have similar affects on liquidus and mineral compositions. Requires Cl rich, water-poor martian mantle Filiberto & Treiman (2009)

12 Age of nakhlites Most radiometric ages of nakhlites strongly suggest a common formation time ~1.3 13Ga However there is a total variation in individual ages over about 0.2 Ga real differences in formation times Martian weathering Recoil effects Trapped 40 Ar components

13 Martian meteorites Iddingsite Iddingsite Carbonate

14 Nahklite meteorites Cooling rate Grain size Burial Depth NWA 817 MIL FAST Small 1-2 m ~ 4 m Y /000749/ Nakhla + Governador Valadares 7 m ~ 10 m Lafayette NWA 998 SLOW Large > 30 m >> 30 m Igneous Cumulate Suite (Mikouchi et al., 2003, 2006; Nyquist et al., 2001; Treiman, 2005)

15 Nakhla crushing results Crushing experiments old apparent ages ~ Ma. Age (Ma) 1300 Ma = Suggests a trapped component is present in low retention sites.

16 Ar and Cl in brines bi boiling or salinity increase Mantle fluids in diamonds Ar/ 36 Ar 1000 Cu-porphyry 10-6 Increasing radiogenic or mantle input AIR 0 25 C Seawater typical groundwaters Cl/ 36 Ar ( 10 6 )

17 Nakhla and NWA 998 crushing Highest 40 Ar/ 36 Ar ratios v. high ages high h Cl/ 36 Ar ratios Ar/ 36 Ar 40 A Cl/ 36 Ar

18 Nakhla isochron Step-heating experiments apparent ages ~ Ma. Ar 36 Ar/ 40 A 39 Ar/ 40 Ar Little evidence for mixing with terrestrial air or Martian interior. Crushing samples give old ages.

19 Argon isochrons Trapped Terrestrial atmosphere argon Martian atmosphere (Viking) 3000 ± 500 Meteorites r/ 40 Ar 36 Ar Mars interior (meteorites) Radiogenic argon older ages 39 Ar/ 40 Ar younger ages

20 NWA 998 stepped heating 36 Ar/ Ar 39 Ar/ 40 Ar

21 NWA 998 trapped Ar Trapped component Released at high temp. from olivine and pyroxene 6 Ar/ 40 Ar 3 40 Ar/ 36 Ar ~ 282 ± 8 Martian interior? Terrestrial atmosphere? 39 Ar/ 40 Ar

22 NWA 998 cosmogenic Ar Cosmogenic argon 40 Ar/ 36 Ar Ar/ 40 Ar 36 Mainly from olivine Cosmogenic 36Ar production from Fe 39 Ar/ 40 Ar

23 NWA 998 Mars atmosphere Ar Mars atmosphere 36 Ar/ 40 Ar 40 Ar/ 36 Ar ~ 1000 Low temperature releases (Cl-rich) Inclusions fluids 39 Ar/ 40 Ar

24 Summary of Ar components Ar 36 Ar/ 40 A 39 Ar/ 40 Ar

25 Martian groundwater Suggests presence of Cl-rich phases with 40 Ar/ 36 Ar 1000.

26 How much fluid? Ar in Martian atmosphere 1.6 % (Owen et al., 1977) 40 Ar/ 36 Ar 1900 (Bogard and Garrison, 1999) Martian surface pressure atm Partial pressure at surface = 8.3 x 10-6 atm Ar Henry constant at 0 C = mol/l/atm Moles of 36 Ar per litre of water on Mars = 173x Nakhla results: 36 Ar concentration x cm 3 /g = ml of water per kg of material

27 Salinity estimate Nakhla Crush experiments Cl/ 36 Ar ~ x x 10-8 moles of 36 Ar per litre of water on Mars Salinity range of grams of Cl per litre of water. (Cl concentration of seawater = 19 g/l)

28 Nakhla halogens Cl and I abundances similar to terrestrial basalts Show overall Br enrichments similar il to martian soils and rocks Br enrichment related to martian weathering (olivine)

29 Halogens martian meteorites Same level of halogen variation as seen on Earth Non-chondritic composition. No obvious endmember compositions (yet). Halogen fractionation in absence of biochemistry.

30 Summary 1) Fluid component Cl rich & 40 Ar correlation 40 Ar/ 36 Ar ~ 1000 Released in crush & low temp. analysis Fluid inclusions - a low salinity fluid on Mars 2) Trapped component 40 Ar/ 36 Ar Released in mid-high temps Could be terrestrial t OR Martian interior. i 3) Cosmogenic Fe 40 Ar/ 36 Ar ~ 100 Cosmogenic 36 Ar formed from Fe in olivine. 4) Halogens Highly variable Br/Cl and I/Cl Martian weathering gives elevated Br/Cl Origin of the halogen fractionations are unknown

Martian Meteorites 1

Martian Meteorites 1 The SNCs How do we know the SNCs are from Mars? [Taylor & McLennan, 2009] 2 The SNCs Abundances and isotopic compositions of gases trapped in impact melt glasses match those measured