Early Palaeozoic Evolution of the Paleo‐Asian Ocean: Evidence From <scp>SSZ</scp> Ophiolites and Adakites, Central Inner Mongolia, North China

ABSTRACT Understanding the Early Palaeozoic evolution of the Paleo‐Asian Ocean (PAO) is critical for reconstructing the accretionary processes of the Central Asian Orogenic Belt (CAOB). Here, we present a systematic study of supra‐subduction zone (SSZ) ophiolites and adakites from central Inner Mongolia, North China, to elucidate the subduction dynamics of the PAO. Zircon U–Pb dating results indicate that the SSZ‐type ophiolitic rocks formed at ~490 Ma, whereas the adakitic trondhjemites yield a crystallisation age of ~448 Ma. The metagabbros exhibit tholeiitic affinities and are characterised by high Mg contents, enrichment in LILEs and depletion in HFSEs, indicating a subduction‐related origin. The quartz diorites, identified as newly discovered plagiogranites, display SSZ‐type geochemical characteristics with high SiO 2 , low K 2 O and enriched HFSEs, suggesting that the plagiogranites in the Tulinkai ophiolite are similar to plagiogranites derived from partial melting. The adakitic trondhjemites are characterised by high SiO 2 , Al 2 O 3 , Sr and Sr/Y ratios, low Y and Yb contents, and positive Eu anomalies, suggesting their derivation from the partial melting of subducted basaltic oceanic crust. The zircon positive ε Hf ( t ) values support a derivation from juvenile crust. Integrating these findings with regional geological data, we propose that southward subduction of the PAO was already established by ~490 Ma along the Ondor Sum‐Tulinkai belt, followed by sustained SSZ magmatism and adakitic magmatism, reflecting a long‐lived subduction system along the southern CAOB during the Early Palaeozoic.