Abstract:This study undertookelectron microprobe, zirconU- Pb dating and petrographic, geochemical analyses onthehornblendite firstly recognized in the Bayandulan of Dong Ujimqi to understand the characteristics of the late Paleozoic mantle nature and structure. In these rocks, mainrockformingminerals are hornblende, someplagioclase and magnetite.The dating results indicate that the hornblendite formed in the Late Carboniferous 310±1 Ma. The geochemical data of the samples show SiO 2 (48. 66%~52. 50%), MgO (11. 53%~13. 10%), Al 2O 3 (10. 11%~12. 18%), Na 2O+K 2O (2. 21%~3. 13%, <3. 5%, m/f (0. 36~0. 45), Mg #(70. 27~74. 54), TFeO(7. 77%~10. 14%). The standardized distribution pattern of REE chondrites is right- leaning with relatively enriched LREE.The rocks are enriched in LILE (Rb, K), and depleted in HFSE (Nb, Ta, Ti), and there are obvious negative anomalies of Nb, Ta and Ti. Electron probe analyses results show that hornblende belongs to calcic amphibole and has the characteristics of mantle hornblende. The ε Hf ( t ) values of zircons from the hornblendite vary between 7. 47~15. 54, and their Hf one- stage model ages vary from 847 to 332 Ma, implying that their magma source was derived from a depleted mantle.Combined with regional tectonic evolution, the hornblendite formed in the subduction setting of the Paleo- Asian Ocean.This discovery provides rock evidence for the late Paleozoic mantle tectonomagmatic evolution.