The Urad Zhongqi mafic intrusions crop out in western Inner Mongolia and are dominated by horn- blende gabbro． Zircon LA- ICP- MS U- Pb dating indicates that the mafic pluton was emplaced in the Early Per- mian (272 ±3Ma)． The hornblende gabbro rocks have low concentrations of SiO 2 ， high total Fe 2 O 3 ， MgO， Ni， Co，Sc and Cr． The rocks are characterized by selective enrichment of large ion lithophile elements (LILE) and light rare earth elements (LＲEE)，and depletion in high field strength elements (HFSE) (e． g． Nb，Ta，Zr， Hf，P and Ti)． It suggests that they formed from a primary magma generated by the partial melting of lithos- pheric mantle material had been previously modified by subduction- related fluids． According to the geochemical data and the geology of the region，the authors found that the Early Permian hornblende gabbroic in western In- ner Mongolia formed in a post- collisional extensional setting．