Crystallization of baddeleyite in basaltic rocks from Mars and comparisons with the Earth, Moon, Mars, and Vesta

Baddeleyite (ZrO2) is a relatively common accessory mineral in planetary igneousrocks and a key mineral chronometer for dating planetary processes. We review several methods for locating and characterizing baddeleyite grains, which are typically small (< 20 μm), and provide an overview of the occurrence of baddeleyite in mafic rocks from Mars (shergottites), the Moon (lunar meteorites) and the asteroid Vesta (eucrites). As with occurrences in igneous rocks from Earth, baddeleyite forms from late-stage igneous melt in all of these planetarysamples, associated with ferroan pyroxene and olivine, Fe-Ti oxides, sulfides and phosphates. Similarities in internal zoning as revealed by cathodoluminescence occur in baddeleyite in samples from Earth, the Moon and Vesta, although strong luminescence is lacking in baddeleyite from shergottites. We conclude that baddeleyite is a common late-stage crystallization product inplanetary basaltic rocks that derive from relatively Zr-rich parental melts in which Zr remains incompatible during crystallization.