A contact zone sandwiched between an arc and an oceanic crust was discovered in the Laohushan area in the present study. It consists of a series of north-dipping imbricated thrust sheets and is exposed on the surface as a narrow arcuate belt, which extends for about 30 km in an E-W direction and measures about 1-3 km wide. Lithologically, it can be divided into four subzones. Subzone 1 consists of meta-andesite and metasandstone; subzone 2, psammitic schists; subzone 3, psammitic and pelitic schists, quartz diorite and hornfelses; and subzone 4, metagabbro, epidote amphibolite and pelitic schists. The metamorphism has the following grading sequence: low greenschist facies in subzone 1 → high greenschist facies in subzone 2 →low amphibolite facies in subzone 3→ epidote amphibolite facies in subzone 4. Petrographic and geochemical evidence shows that rocks in subzones 1, 2 and 3 are arc rocks, whereas those of subzone 4 are oceanic crustal rocks. The metamorphic mineral assemblages and especially miner