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Microstructures and Microanalysis in ALH84001: Minerals or Martians?

Published online by Cambridge University Press:  02 July 2020

Ralph P. Harvey ,
John Bradley  and
Harry Y. McSween Jr.
Ralph P. Harvey
Affiliation:
Department of Geological Sciences, Case Western Reserve University, ClevelandOH44106-7216
John Bradley
Affiliation:
MVA Inc., 5500 Oakbrook Parkway #200, Norcross, GA30093; School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA30332-0245
Harry Y. McSween Jr.
Affiliation:
Department of Geological Sciences, University of Tennessee, KnoxvilleTN37996-1410
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Extract

The martian meteorite ALH84001 leapt into the spotlight in late 1996 when a NASA-led research team suggested that it contained evidence of biotic activity on ancient Mars. ALH84001 is unique among the martian meteorites- a cumulate rock made up predominantly of orthopyroxene, with interstitial maskelynite (feldspar turned into a diaplectic glass by shock), apatite, chromite and sulfides. Highly brecciated fracture zones cut through the rock, presumably a result of impacts, and within these zones is a variable amount of secondary carbonate. This carbonate, the most extensive secondary mineral found in any martian meteorite, formed during significant interaction between martian crust and volatiles, and represents a unique access point toward understanding the environment of ancient Mars. However, the conditions under which this carbonate formed are less clear. While claims for evidence of biotic activity are predicated on carbonate formation at low (<100°C) temperatures under water-rich conditions, other research suggests much less hospitable conditions, with little water present and formation temperatures approaching 700°C.

Type
Microscopy of Ceramics and Minerals
Information
Microscopy and Microanalysis , Volume 4 , Issue S2: Proceedings: Microscopy & Microanalysis '98, Microscopy Society of America 56th Annual Meeting, Microbeam Analysis Society 32nd Annual Meeting, Atlanta, Georgia July 12-16, 1998 , July 1998 , pp. 604 - 605
Copyright
Copyright © Microscopy Society of America

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References

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