The North Wulan terrane representing the overriding plate of the Early Paleozoic subduction-collision system of North Qaidam Orogen, is key to understanding the composition of the lower part of the crust beneath arc?back-arc and the tectonic evolution of the subduction process of the South Qilian Proto-Tethyan oceanic crust. In this paper, we present detailed petrology, geochronology, geochemistry and metamorphic P?T condition of the representative mafic to felsic metamorphic rocks in the North Wulan Terrane. The results reveal that the protolith age and tectonic setting of the three types of metamorphic rock studied are significantly different. The amphibolites exhibit compositional characteristics similar to E-MORB, but it does not retain information about the protolith age and thus cannot be further discussed in terms of its significance. The biotite-amphibole gneisses display geochemical signatures of continental arc, with protoliths formed at 471 ± 3 Ma, representing magmatic records of the continental marginal arc during the subduction of the Proto-Tethyan oceanic crust. The granitic mylonites exhibit geochemical feature resembling arc granite and formed at 965 ± 6 Ma, which means that they represent arc magmatism in an active continental margin setting related to the assembly of the Neoproterozoic supercontinent Rodinia. Combined with previous studies, it is proposed that the composition of the lower part of the crust beneath arc?back-arc, represented by the North Wulan Terrane, are primarily composed of Precambrian basement (including various types and ages of metasedimentary and meta-igneous rocks) and Early Paleozoic continental arc magmatic rocks. These rocks were widely subjected to Middle-Late Ordovician HT/LP metamorphism, with the corresponding metamorphic ages concentrated around ca. 475–440 Ma. This period is notably confined to the late stage of oceanic subduction, as recorded by arc magmatism (ca. 510–450 Ma), and is nearly synchronous with the eclogite-facies metamorphic ages associated with subduction of oceanic crust documented in the Dulan UHP unit. Integrating previous studies on metamorphic P?T evolution, we suggest that the HT/LP metamorphism occurring under an extensional environment of the continental marginal arc during the late stage of plate convergence is caused by slab rollback. This highlights the critical role of studying metamorphism of the overriding plate of subduction zones for reconstructing the tectonic evolution of subduction of oceanic crust.