Ultrarefractory inclusions in the Sayh al Uhaymir 290 CH carbonaceous chondrite
Konstantin M. Ryazantsev, Marina A. Ivanova, Alexander N. Krot, Chi Ma, Cyril A. Lorenz, Vasily D. Shcherbakov
MAPS, Version of Record online: 24 July 2025
“Ultrarefractory Ca,Al-rich inclusions (UR CAIs) in the Sayh al Uhaymir (SaU) 290 CH3 carbonaceous chondrite consist of ultrarefractory Zr,Sc-rich minerals (allendeite, kangite, tazheranite, warkite, and Y-perovskite), grossite, grossmanite, hibonite, melilite, and spinel. Several of them have a core–mantle structure with ultrarefractory minerals concentrated in the core. The unfragmented inclusions are surrounded by layers of spinel, melilite, Sc-diopside, and diopside (not all layers are present around individual inclusions). The UR CAIs have uniform 16O-rich compositions: Most inclusions have Δ17O of ~ −23 ± 2‰; a grossite-rich CAI is slightly 16O-depleted (Δ17O ~ −17‰). The CAIs are highly enriched in Zr, Hf, Sc, Y, and Ti compared to typical and previously studied UR CAIs from CM2, CO3, and CV3 carbonaceous chondrites. Similar to UR CAIs from other chondrites, the ultrarefractory minerals in SaU 290 CAIs are enriched in heavy rare earth elements (HREEs) relative to more volatile light rare earth elements (LREEs). We conclude that (1) UR CAIs from SaU 290 formed by gas–solid condensation from a gaseous reservoir having variable but mostly solar-like O-isotope composition, most likely near the proto-Sun, and were subsequently transported outward to the accretion region of CH chondrites. (2) The UR oxides and silicates are important carriers of UR REE patterns recorded their possible early fractionation.”
