Multicarbonatites of the world’s largest REE deposit juxtaposed by Mesozoic thrusts at Bayan Obo, China

• Geological and geophysical data constrain two thrust faults transported carbonatites northward. • Mesozoic thrust faults stacked carbonatites at Bayan Obo facilitating formation of the giant REE deposit. • Preserved carbonatite roots at south indicate further untapped REE resource potential. Increasing demand for critical rare earth elements (REEs), commonly sourced in carbonatites, underscores the need to understand deep deposit architecture. The world’s largest REE deposit, Bayan Obo, originated from mantle-derived carbonatite magma, yet occurs at shallow level, as indicated by geophysical anomalies. We provide a detailed investigation of two thrust faults: the F1 fault along Haoqin-North Jianshan, and the F2 fault extending from Boluotou-East Contact Zone-Dongjielegele to southern West Pit. The F1 fault displaces Paleo-Mesoproterozoic strata and Boluotou, East-Main-West Pit, and Dongjielegele carbonatite (Ca1) over footwall Early Paleozoic strata, whose youngest age peaks (1.14–1.29 Ga) are younger than the carbonatites. Ca1 carbonatite is restricted above ∼ 2.5 km, with high V s , low resistivity, and high magnetic susceptibility. The Shuiyuantou klippen and low-resistivity anomalies between Bayan Obo and C2 (MT profile) constrain ∼ 14 km northward displacement by the F1 fault. The F2 fault thrusts carbonatite at East Contact zone and southern West Pit (Ca2), intruded by Permian granite with skarnization, over Ca1 carbonatite and Paleo-Mesoproterozoic strata in the F1 hanging-wall. This fault dips southward from outcrop to > 100 m and up to 1320 m depth, constrained by drill-holes and seismic reflection profile; four en echelon high aeromagnetic anomalies and lithologic correlations indicate ∼ 30 km displacement. Both faults cut Permian granites and are overlain by Cretaceous strata, consistent with Jurassic activity of regional thrusting in northern NCC. The F1 and F2 faults transported and stacked Ca1 and Ca2 carbonatites at Bayan Obo, forming the world’s largest REE deposit. These interpreted magmatic roots represent priority targets for future geophysical refinement and deep drilling, although their REE grade and economic significance remain to be tested.