Trace Element Transport and Deposition During Magmatic Degassing: The Effect on Martian Rocks and Fines

Abstract Martian magmas compositionally resemble those from terrestrial continental hotspot magmatic suites, characterized by low OH and high Cl and S contents. The magmatic gases exsolved from such magmas transport a variety of metal complexes and, upon cooling, precipitate vapor‐deposits into vugs and fractures within rocks and on the surfaces of pyroclastics, which are then added to surface fines. Experiments investigated trace element behavior during magmatic degassing as a potential signature of this magmatic process. Low‐pressure experimental degassing of P‐rich basaltic magma containing Cl, Br, S, minor OH, and trace elements (Sr, Ge, Ga, Zn, Pb, Rb, Cs, Se, Cu, La, and Lu) demonstrated that the gas‐transported trace metals become incorporated into vapor‐deposited Cs‐Pb‐Zn‐Rb‐bearing halides, Ge‐Ga‐bearing iron oxides, Zn‐Se‐Cu‐bearing sulfides, alkali and iron sulfates, Ge‐bearing silicates, rare earth phosphates, and elemental metals. Low‐OH and high‐Cl magmatic systems produce a variety of halides but inhibit Fe‐oxide formation. S‐rich systems produce vapor‐deposited Na‐, K‐, and Fe‐sulfates, Zn‐Cu‐Se bearing sulfides, and iron oxides. These results provide a signature for determining the possibility of a significant role for magmatic gas in producing secondary minerals and volatile trace element enrichment in the Gusev plains, Columbia Hills, Jezero crater, and Gale crater. A hallmark of vapor‐deposited phases is the presence of local heterogeneities in “alteration” phases and in trace element signatures due to the superposition of high and low temperature phases.