Vapor-Deposited Minerals Contributed to the Martian Surface During Magmatic Degassing

Martian magmas were likely enriched in S and Cl with respect to H₂O. Exsolution of a vapor phase from these magmas and ascent of the gas bubbles through the magma plumbing system would have given rise to shallow magmas that were gas-charged. Release and cooling of this gas from lava flows during eruption may have resulted in the addition of a significant amount of vapor-deposited phases to the fines of the surface. Experiments were conducted to simulate degassing of gas-charged lava flows and shallow intrusions in order to determine the nature of vapor-deposited phases that may form through this process. The results indicate that magmatic gas may have contributed a large amount of Fe, S, and Cl to the Martian surface through the deposition of iron oxides (magnetite, maghemite, and hematite), chlorides (molysite, halite, and sylvite), sulfur, and sulfides (pyrrhotite and pyrite). Primary magmatic vapor-deposited minerals may react during cooling to form a variety of secondary products, including iron oxychloride (FeOCl), akaganéite (Fe³⁺O (OH,Cl)), and jarosite (KFe³⁺₃(OH)₆(SO₄)₂). Vapor-deposition does not transport significant amounts of Ca, Al, or Mg from the magma and hence, this process does not directly deposit Ca- or Mg-sulfates.