TY - JOUR
T1 - The Northwest Africa (NWA) 5790 meteorite
T2 - A mesostasis-rich nakhlite with little or no Martian aqueous alteration
AU - Tomkinson, Tim
AU - Lee, Martin R.
AU - Mark, Darren F.
AU - Dobson, Katherine J.
AU - Franchi, Ian A.
PY - 2015/2
Y1 - 2015/2
N2 - Northwest Africa (NWA) 5790 is the most recently discovered member of
the nakhlite group. Its mineralogy differs from the other nakhlites with
a high abundance mesostasis (38.1 ± 3.6 vol%) and scarcity of
olivine (4.0 ± 2.2 vol%). Furthermore, zoning of augite
phenocrysts, and other petrographic and chemical characteristics suggest
that NWA 5790 samples the chilled margin of its parent lava flow/sill.
NWA 5790 contains calcite and rare clay minerals that are evidence for
its exposure to liquid water. The calcite forms a cement to coatings of
dust on the outer surface of the find and extends into the interior of
the meteorite within veins. The presence of microbial remains within the
coating confirms that the dust and its carbonate cement are terrestrial
in origin, consistent with the carbon and oxygen isotope composition of
the calcite. The clay minerals are finely crystalline and comprise
~0.003 vol% of the meteorite. δD values of the clay minerals range
from -212 ± 109‰ to -96 ± 132‰, and cannot
be used to distinguish between a terrestrial or Martian origin. As
petrographic results are also not definitive, we conclude that secondary
minerals produced by Martian groundwaters are at best very rare within
NWA 5790. The meteorite has therefore sampled a region of the lava
flow/sill with little or no exposure to the aqueous solutions that
altered other nakhlites. This isolation could relate to the scarcity of
olivine in NWA 5790 because dissolution of olivine in other nakhlites by
Martian groundwaters enhanced their porosity and permeability, and
provided solutes for secondary minerals.
AB - Northwest Africa (NWA) 5790 is the most recently discovered member of
the nakhlite group. Its mineralogy differs from the other nakhlites with
a high abundance mesostasis (38.1 ± 3.6 vol%) and scarcity of
olivine (4.0 ± 2.2 vol%). Furthermore, zoning of augite
phenocrysts, and other petrographic and chemical characteristics suggest
that NWA 5790 samples the chilled margin of its parent lava flow/sill.
NWA 5790 contains calcite and rare clay minerals that are evidence for
its exposure to liquid water. The calcite forms a cement to coatings of
dust on the outer surface of the find and extends into the interior of
the meteorite within veins. The presence of microbial remains within the
coating confirms that the dust and its carbonate cement are terrestrial
in origin, consistent with the carbon and oxygen isotope composition of
the calcite. The clay minerals are finely crystalline and comprise
~0.003 vol% of the meteorite. δD values of the clay minerals range
from -212 ± 109‰ to -96 ± 132‰, and cannot
be used to distinguish between a terrestrial or Martian origin. As
petrographic results are also not definitive, we conclude that secondary
minerals produced by Martian groundwaters are at best very rare within
NWA 5790. The meteorite has therefore sampled a region of the lava
flow/sill with little or no exposure to the aqueous solutions that
altered other nakhlites. This isolation could relate to the scarcity of
olivine in NWA 5790 because dissolution of olivine in other nakhlites by
Martian groundwaters enhanced their porosity and permeability, and
provided solutes for secondary minerals.
U2 - 10.1111/maps.12424
DO - 10.1111/maps.12424
M3 - Article (Academic Journal)
SN - 1086-9379
VL - 50
SP - 287
EP - 304
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
IS - 2
ER -
