Aqueous alteration of the CM carbonaceous
chondrites has produced a suite of secondary
minerals, and differences between meteorites in
their abundance defines a progressive alteration sequence
[e.g. 1, 2]. The means by which this water
gained access to the original anhydrous constituents of
the meteorites is the subject of considerable debate.
Studies of rock texture, mineralogy and bulk chemical
composition have concluded that solutions were generated
by the melting of water ice in situ, and remained
essentially static as a consequence very low intergranular
permeabilities [e.g. 3, 4]. By contrast, results of
oxygen isotope work and modelling have suggested
that the fluids moved considerable distances within the
parent body [5, 6]. Given the intergranular permeability
of the CMs, an extensive fracture network would be
required to support such flow.
Clues to how the two very different models for
aqueous alteration of the CMs can be reconciled have
been recently provided by Rubin [7]. He recognised a
good correlation between the magnitude of impact-induced
compaction of CM meteorites and their degree
of aqueous processing, with the more highly deformed
meteorites being more altered. Here we have asked
whether compaction was accompanied by the development
of fracture networks that could have provided the
conduits for aqueous solutions that mediated all or
some of the alteration