Isotopic composition of carbonates in the SNC meteorites, Allan Hills 84001 and Zagami

We have measured the 13 C/ 12 C and 14 C/ 12 C ratios in CO 2 released by acid etching of the meteorites Zagami and Allan Hills 84001. We use the 14 C as a label to identify extraterrestrial carbonate phases, as they will have a low 14 C/ 12 C ratio (< - 4% modern terrestrial ratio) compared to recent terrestrial material. The new studies on Allan Hills 84001 confirm previous conclusions that the Fe, Mg-rich carbonate grains in this meteorite contain carbon with δ 13 C as high as +45 ‰. In contrast, the carbon released from Zagami is depleted in 13 C with δ 13 C as low as -20‰. We conclude that the isotopic composition of the carbon as carbonate released from acid etching of Zagami is different from the carbonates observed in both Allan Hills 84001 and Nakhla. With the assumption that all of these meteorites sample the surface of Mars, we propose that the Zagami carbonate samples a different carbon reservoir on this planet, such as a magmatic source. With this interpretation, the high δ 13 C values of carbonate observed in Allan Hills 84001 and Nakhla can be ascribed to a fractionated source compared with the originally light carbon. A likely origin for this 13 C-enriched component is an isotopically heavy Martian atmosphere; however, given the possibility of biological activity involving Allan Hills carbonates, we cannot exclude this as a source of the isotopic fractionation.

[1]  B. Jakosky.  Mars volatile evolution: Evidence from stable isotopes , 1991 .

[2]  A. Jull,et al.  Studies of cosmogenic in-situ 14CO and 14CO2 produced in terrestrial and extraterrestrial samples: experimental procedures and applications , 1994 .

[3]  L. Anovitz,et al.  Phase Equilibria in the System CaCO3-MgCO3-FeCO3 , 1987 .

[4]  R. Zare,et al.  Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 , 1996, Science.

[5]  High-precision decadal calibration of the radiocarbon time scale, AD 1950-2500 BC. , 1986 .

[6]  J. R. O'neil,et al.  Compilation of stable isotope fractionation factors of geochemical interest , 1977 .

[7]  M. Stuiver,et al.  Discussion: Reporting of 14 C Data , 1977 .

[8]  R. Clayton,et al.  Water in SNC meteorites: evidence for a martian hydrosphere. , 1992, Science.

[9]  H. Craig,et al.  Oxygen isotope variations in marginal basin and ocean-ridge basalts , 1976 .

[10]  Karl Munnich Ingeborg Levin.  25 Years of trospheric 14C observations , 1985 .

[11]  B. Jakosky.  Mars volatile evolution: Implications of the recent measurement of 17O in water from the SNC meteorites , 1993 .

[12]  H. Ohmoto,et al.  Chapter 2. KINETICS of ISOTOPIC EXCHANGE at ELEVATED TEMPERATURES and PRESSURES , 1986 .

[13]  C. Pillinger,et al.  Chassigny and the nakhlites: Carbon-bearing components and their relationship to martian environmental conditions , 1992 .

[14]  R. Ash,et al.  A 4-Gyr shock age for a martian meteorite and implications for the cratering history of Mars , 1996, Nature.

[15]  I. P. Wright,et al.  Record of fluid–rock interactions on Mars from the meteorite ALH84001 , 1994, Nature.

[16]  C. Pillinger,et al.  Carbon, oxygen and nitrogen isotopic compositions of possible martian weathering products in EETA 79001 , 1988 .

[17]  R. Clayton,et al.  Isotopic Composition of Carbonate in EETA 79001 and its Relation to Parent Body Volatiles , 1988 .

[18]  J. Hoefs.  Stable Isotope Geochemistry , 2015 .

[19]  Michael E. Zolensky,et al.  Calcium carbonate and sulfate of possible extraterrestrial origin in the EETA 79001 meteorite , 1988 .

[20]  Harry Y. McSween,et al.  What we have learned about Mars from SNC meteorites , 1994 .

[21]  Harry Y. McSween,et al.  A possible high-temperature origin for the carbonates in the martian meteorite ALH84001 , 1996, Nature.

[22]  D. Mittlefehldt,et al.  ALH84001, a cumulate orthopyroxenite member of the martian meteorite clan , 1994 .

[23]  B. Taylor.  Magmatic volatiles; isotopic variation of C, H, and S , 1986 .

[24]  M. Velbel,et al.  Rapid Growth of Magnesium-Carbonate Weathering Products in a Stony Meteorite from Antarctica , 1988, Science.

[25]  R. Clayton,et al.  Oxygen isotopes in shergotty , 1986 .

[26]  F. Mackenzie,et al.  Magnesian calcites; low-temperature occurrence, solubility and solid-solution behavior , 1983 .

[27]  S. Sheppard,et al.  An isotopic study of siderites, dolomites and ankerites at high temperatures☆ , 1986 .

[28]  M. McElroy,et al.  Isotopic Composition of the Martian Atmosphere , 1976, Science.

[29]  F. Pineau,et al.  Carbon isotopes and concentrations in mid-oceanic ridge basalts , 1983 .

[30]  D. Donahue,et al.  Carbon-14 activities in recently fallen meteorites and Antarctic meteorites , 1989 .

[31]  D. Donahue,et al.  Carbon‐14 terrestrial ages and weathering of 27 meteorites from the southern high plains and adjacent areas (USA) , 1993 .

[32]  H. Ohmoto.  Systematics of Sulfur and Carbon Isotopes in Hydrothermal Ore Deposits , 1972 .

[33]  C. Eastoe,et al.  Isotopic composition of carbonates in the SNC meteorites Allan Hills 84001 and Nakhla , 1995 .

[34]  M. Grady,et al.  Martian atmospheric carbon dioxide and weathering products in SNC meteorites , 1985 .

[35]  L. Leshin,et al.  HYDROGEN ISOTOPE GEOCHEMISTRY OF SNC METEORITES , 1996 .

[36]  C. Pillinger,et al.  The carbon and oxygen isotopic composition of meteoritic carbonates , 1988 .

[37]  D. Donahue,et al.  Isotope-Ratio and Background Corrections for Accelerator Mass Spectrometry Radiocarbon Measurements , 1990, Radiocarbon.

[38]  H. Ohmoto.  Isotopes of sulfur and carbon , 1979 .

[39]  T. K. Kyser.  Chapter 5. STABLE ISOTOPE VARIATIONS in the MANTLE , 1986 .