Thanks for the post on apatite, T.
The Wiki article on ALH84001 notes that "It contains polycyclic aromatic hydrocarbons (PAHs) concentrated in the regions containing the carbonate globules, and these have been shown to be indigenous."
Moreover, "In October 2011 it was reported that isotopic analysis indicated that the carbonates in ALH84001 were precipitated at a temperature of 18 °C (64 °F) with water and carbon dioxide from the Martian atmosphere. The carbonate carbon and oxygen isotope ratios imply deposition of the carbonates from a gradually evaporating subsurface water body, probably a shallow aquifer meters or tens of meters below the surface."
Since the concentration of PAHs increase with increasing penetration into the rock, it is unlikely a contaminant from earth. One wonders what the H/D ratios in the PAHs might be, and how it compares to the apatite. Since they only looked at this in the apatite, it would be interesting to have these numbers. PAHs are found throughout the universe, and their presence on Mars would not come as a surprise. However, where these hydrocarbons formed would play a significant role in evaluating their relationship to H/D ratios in Martian rocks.
If the PAHs on Mars were formed elsewhere (quite possible), some of them could have degraded on an early Mars, and mixed with the non-organic H/D ratios originally present. Clearly not a simple study.
Both the carbonates and apatites likely formed from aqueous intrusions. Since Wiki further notes that ALH84001 crystallized about 4 bya, it seems reasonable that an inherent porosity of the rock must have allowed such penetration, as the rock lay within a subsurface water source long after its formation. This would eliminate any requirement for the existence of PAHs or the minerals in the original melt. Now one wonders when this mineral/PAH intrusion occurred. Not sure if I missed such a proposition in all the stuff I have been reading............
en.wikipedia.org
en.wikipedia.org