ALH 84001 MARTIAN METEORITE
This transmitted light microscope image at 50X of the Allan Hills 84001 Martian meteorite shows several brown rounded carbonate globules formed when this meteorite was forming part of Mars' surface. This Martian meteorite is an ultramafic and ultrabasic rock that is almost exclusively made from the mineral orthopyroxene (orange dominated colours in the image). ALH 84001 is an igneous orthopyroxene cumulate containing clear shock deformation textures and fractures and secondary extraterrestrial carbonates.
Our CSIC-IEEC research group studied this rock and demonstrated that Martian meteorites can provide valuable information about past environmental conditions on Mars. Allan Hills 84001 formed more than 4 Gyr ago, and owing to its age and long exposure to the Martian environment, this meteorite has features that record early processes. These features include a highly fractured texture, gases trapped during one or more impact events or during formation of the rock, and spherical Fe-Mg-Ca carbonates. Our MAPS research paper provided new insights into the context of the origin of these carbonates. Their petrographic features and compositional properties indicate that at least two pulses of Mg- and Fe-rich solutions saturated the rock. Those two generations of carbonates can be distinguished by a very sharp change in compositions, from being rich in Mg and poor in Fe and Mn, to being poor in Mg and rich in Fe and Mn. This evidence could point to significant chemical changes in the outgassed atmosphere of a wet early Mars environment.
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