Paleomagnetic Evidence of a Low-Temperature Origin of Carbonate in the Martian Meteorite ALH84001

Indirect evidence for life on Mars has been reported from the study of meteorite ALH84001. The formation temperature of the carbonates is controversial; some estimates suggest 20° to 80°C, whereas others exceed 650°C. Paleomagnetism can be used to distinguish between these possibilities because heating can remagnetize ferrimagnetic minerals. Study of two adjacent pyroxene grains from the crushed zone of ALH84001 shows that each possesses a stable natural remanent magnetization (NRM), implying that Mars had a substantial magnetic field when the grains cooled. However, NRM directions from these particles differ, implying that the meteorite has not been heated significantly since the formation of the internal crushed zone about 4 billion years ago. The carbonate globules postdate this brecciation, and thus formed at low temperatures.

[1]  S. Cisowski.  Magnetic studies on Shergotty and other SNC meteorites , 1986 .

[2]  E. Shock,et al.  A geochemical model for the formation of hydrothermal carbonates on Mars , 1995, Nature.

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

[4]  H. McSween,et al.  Magnetite whiskers and platelets in the ALH84001 Martian meteorite: evidence of vapor phase growth. , 1996, Geochimica et cosmochimica acta.

[5]  M. McElhinny,et al.  The combined analysis of remagnetization circles and direct observations in palaeomagnetism , 1988 .

[6]  J. Kirschvink.  The least-squares line and plane and the analysis of palaeomagnetic data , 1980 .

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

[8]  J. Gooding.  Soil mineralogy and chemistry on Mars - Possible clues from salts and clays in SNC meteorites , 1992 .

[9]  J. Kirschvink,et al.  Ultrastructure, morphology and organization of biogenic magnetite from sockeye salmon, Oncorhynchus nerka: implications for magnetoreception. , 1988, The Journal of experimental biology.

[10]  M. Burkland,et al.  Noble gases in orthopyroxenite ALH84001: A different kind of martian meteorite with an atmospheric signature , 1995 .

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

[12]  Masaru Kono,et al.  Some global features of palaeointensity in geological time , 1995 .

[13]  G. Layne,et al.  Hydrothermal Systems on Mars. Insights from Sulfur Isotopic Systematics in Alteration Assemblages in Martian Meteorite Allan Hills 84001 , 1996 .

[14]  M. Dekkers.  Magnetic properties of natural pyrrhotite. II. High- and low-temperature behaviour of Jrs and TRM as function of grain size , 1989 .

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

[16]  S. Cisowski,et al.  Interacting vs. non-interacting single domain behavior in natural and synthetic samples , 1981 .

[17]  H. Johnson,et al.  Stability of Anhysteretic Remanent Magnetization in Fine and Coarse Magnetite and Maghemite Particles , 1975 .

[18]  S. Runcorn.  The formation of the lunar core , 1996 .

[19]  M. Dekkers.  Magnetic properties of natural pyrrhotite Part I: Behaviour of initial susceptibility and saturation-magnetization-related rock-magnetic parameters in a grain-size dependent framework , 1988 .

[20]  A. Treiman.  A petrographic history of martian meteorite ALH84001: Two shocks and an ancient age , 1995 .

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