Crystallization of Baddeleyite in Basaltic Rocks from Mars, and Comparisons with the Earth, Moon, and Vesta

Baddeleyite (ZrO2) is an accessory mineral that occurs in variable abundances in planetary basaltic rocks, depending on melt compositions and crystallization conditions. Location and characterization of baddeleyite in a range of planetary basaltic rocks by both automated and manual electron microbeam methods reveals random distributions of grains exhibiting planar and sometimes concentric cathodoluminescent banding. Results from basaltic martian meteorites (shergottites) are emphasized, as their conditions of crystallization are representative of the broad range observed for other planetary basaltic rocks including lunar meteorites and the asteroidal eucrites. We find that baddeleyite forms from late‐stage igneous melt in all of these planetary samples, associated with ferroan pyroxene and olivine, Fe‐Ti oxides, sulfides, and phosphates, and that it is most common at higher oxygen fugacity (≥⃒ QFM). We conclude that the primary factors affecting baddeleyite occurrence are Zr concentrations in late‐stage melts, SiO2 activity, and oxygen fugacity‐dependent compatibilities of Zr in Fe‐Ti oxides.