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 similar to 0.2. The same ratio in Lafayette secondary salts seems to be similar to 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 similar to 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 similar to 600 Ma ago, whereas the SO3-rich fluids likely percolated into the shergottite source region at similar to 180 Ma (or less) suggesting the possible existence of two types of fluid sources on Mars.