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

Abstract

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.