1. Tianjin Center，China Geological Survey，Tianjin 300170，China; 2. College of Earth Sciences，Jilin University，Changchun 130061，China; 3. School of Resources and Environment，Southwest Petroleum University，Chengdu 610500，China

Chonggenshan ultrabasic rock is the largest block of Hegenshan ophiolite belt，which mainly com- posed by lherzolite，harzburgite and a few dunite lenticular body or mass． Characteristics of petrography and geo- chemistry indicate that the ultrabasic rocks belong to the mantle peridotite sequence at lower- middle part of ophiolite suite． Lherzolite and harzburgite are enrichment in Al，with low differentiation index (DI =0. 1 ～2. 79) and high consolidation index (SI =79. 9 ～89. 62)，representing the remnants of primitive mantle． REE showed weak loss of LREE ，which is similar to Alpine lherzolite． REE of dunite is only 0. 1 times of chondrite，displaying irregular “U- shaped”patterns，which is simlilar to Alpine peridotite and mantle peridotite of SSZ type ophiolite． The large area exposed Chonggenshan lherzolite may represent residual mantle peridotite caused by the early expansion of o- cean basin． The phenomenon of rich in Sr，but low in Ti suggested that the effect on the geochemical structures of mantle peridotite by later subduction．