  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 may 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. Here we have
concentrated on providing new insights into the context of these carbonates
using a range of techniques to explore whether they record multiple
precipitation and shock events. The petrographic features and compositional
properties of these carbonates 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. Between these
two generations of carbonate is evidence for fracturing and local corrosion.
