The nature of Martian fluids based on mobile element studies in salt-assemblages from Martian meteorites

The S, Cl, and Br abundances determined in salt assemblages in Nakhla and Lafayette olivine fracturefillings and in gas‐rich impact‐melt (GRIM) glasses from Shergotty and EET79001 Lithologies A & B using EMPA/EDS/APS X‐ray Microprobe techniques are compared with the S and Cl abundances determined by Gooding and coworkers in similar samples using quadrupole mass‐spectrometric techniques. All the analytical methods yield relatively high Cl and low SO3 abundances in Nakhla indicating a SO3/Cl ratio of ∼0.2. The same ratio in Lafayette secondary salts seems to be ∼2. In the case of GRIM glasses from Shergotty and EET79001 Lith A & Lith B, the SO3 abundance is found to be high whereas the Cl abundance is low yielding a SO3/Cl ratio of ∼5–300 (large errors are associated with these ratios because of low Cl signals). The salts found in Nakhla fracturefillings are inferred to have formed from Cl‐rich fluids (high pH) near nakhlite source region on Mars, whereas the secondary minerals found in shergottite GRIM glasses seem to be associated with SO3‐rich fluids (low pH) near shergottite source region on Mars. The Cl‐rich fluids seem to have infiltrated into the nakhlite source region ∼600 Ma ago, whereas the SO3‐rich fluids likely percolated into the shergottite source region at ∼180 Ma (or less) suggesting the possible existence of two types of fluid sources on Mars.