Mn Carbonates in the Martian Meteorite Nakhla: Possible Evidence of Brine
نویسندگان
چکیده
Introduction: The im port ance of secondary phas es in m art i an met eori t es li es in thei r pot ent i al to provi de cl ues about the mart i an envi ronm ent s res ponsi bl e for thei r form ati on. Duri ng this st udy, we anal yzed a num ber of car-bonat e-beari ng fract ure surfaces from the Nakhl a met eor-i t e. Here we des cri be the phys i cal and chemi cal propert i es of several manganes e-cal ci um-ri ch si deri t es. Addi t i onal l y, we des cri be a pot ent i al model for the form ati on and al-t erat i on of thes e carbonat es, and we suggest cons t rai nt s on t he condi ti ons res pons i ble for their preci pi tat i on. Nakhl a is an ol i vine-beari ng cl i nopyroxeni te wi th mi nor amount s of fel ds par, FeS , and Fe oxi des. S econdary mi neral as sem bl ages incl ude vein fi ll i ng cl ays wi th em bedded iron oxi des , a cal ci um sul fate, amorphous s i li ca, chl orapat i te, hal i t e and carbonat es. B ridges and Grady [1] suggest ed that the carbonat es i n Nakhl a form ed from brine evaporat i on [2, 3]. Isot ope st udi es of the Mn-ri ch si deri t e are al s o cons is t ent wi th form at i on from hy-drot hermal flui ds wi t h an upper T cons t rai nt of ~170C [4]. Experimental Methods: Small (mm-sized) chips from the interior of the Nakhla meteorite were stub mounted using quickset epoxy. These chips were sputter coated with a 50Å coating of platinum prior to imaging and analysis using a JEOL 6340 field emission scanning electron microscope (FESEM). EDS analyses were performed using an IXRF energy dispersive X-ray spectroscopy (EDS) system operating at 15kV accelerating voltage. Carbonates and their micro-geological context: Fe-rich carbonates in Nakhla consitute ~30-100 ppm of the rock [4]. Siderite in Nakhla was initially reported by [5], while small veins of calcium carbonate are mentioned by[6] and further …
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Pii: S0301-9268(00)00122-4
Analyses both support and are in opposition to the hypothesis that the Martian meteorite ALH84001 contains evidence for possible biogenic activity on Mars. New observations in two additional Martian meteorites, Nakhla (1.3 Ga old) and Shergotty (300–165 Ma old) indicate possible biogenic features. Features in the three Martian meteorites compare favorably with the accepted criteria for terrestr...
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