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

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.