Mineralogical Evidence for Highly Evolved Th‐Saturated Magma on Mars

Abstract Thorium‐rich (Th‐rich) geological units have been detected by remote sensing in the Martian crust. However, there is still a lack of mineralogical evidence to constrain the magmatic processes responsible for these anomalies. In this study, we report the first discovery of thorite (ThSiO 4 ) grains within a zircon fragment from Martian regolith breccia meteorite NWA 11220. These zircon‐hosted thorite grains are micron‐sized (<5 μm) individual particles and are associated with magnetite and ilmenite inclusions. Transmission Electron Microscopy analysis shows that the thorite and zircon have become metamict due to radioactive decay, whereas magnetite and ilmenite remain crystalline. This metamict thorite provides mineralogical evidence for a highly evolved, Th‐saturated, and oxidized magmatism on Mars. Furthermore, our findings offer a critical ground‐truth for orbital Th anomalies and provide new insights into thorium reservoirs in the Martian crust.