Objective This study aims to clarify the nature of the mantle source and the magmatic record during the evolution of the Baiheshan Ocean in the north Beishan Orogenic Belt, thereby providing key evidence for understanding the evolution mechanism of accretionary orogens.

Methods This paper presents systematic zircon U-Pb dating, whole-rock major and trace element, and Sr-Nd-Hf isotopic analyses of newly identified intrusive rocks in the Hongliuxia area.

Results This work has identified a new set of sillite intruded at 320±3 Ma in the Hongliuxia area of the southern ophiolitic melange belt, which is the product of the major subduction of the Baiheshan Ocean. The sillite shows high−K calc−alkaline geochemical characteristic and was enriched in large−ion lithophile elements like Rb, Th, U, Sr and light rare earth elements and depleted in high field strength elements like Nb, Ta, Ti, showing characteristics of arc magmatic rocks. The values of ε_Nd(t) and ε_Hf(t) of the sillite range from 3.09 to 4.29 and 5.8 to 12.3 respectively, implying that the magma originated from depleted mantle. It may be the product of partial melting of garnet dipyroperidotite constrained by Yb, La and Sm elements. The primary magma underwent limited fractional crystallization and various degrees of crustal contamination. The Early Permian magmatism represents the tectono−magmatic event at the end of the subduction of Baiheshan Ocean. In this work, the widely distributed porphyritic monzogranite was intruded at 275.6±1.4 Ma, belonging to high−K calc−alkaline I−type grantie. They are enriched in large−ion lithophile elements like Rb, Th, U and light rare earth elements and depleted in high field strength elements like Nb, Ti. The values of ε_Hf(t) and T_DM²of the porphyritic monzogranite vary from 9.1 to 14.6 and 368 to 719 respectively, implying magma originated from partial melting of the juvenile crust from Neoproterozoic to Paleozoic.

Conclusions Combined with regional geological material, the accretionary orogeny in the northern part of the Beishan orogenic belt should have ended in the early to middle Permian.