Palaeozoic Convergence in the Central Beishan Orogenic Belt: Evidences From the Middle Silurian to Early Devonian Intrusive Rocks

The Hongliuhe–Xichangjing ophiolitic belt transects the axial zone of the Beishan Orogenic Belt, a key segment within the southern Central Asian Orogenic Belt (CAOB), serving as a structural boundary for Palaeozoic terrane amalgamation. The Middle Silurian–Early Devonian intrusive rocks distributed along both flanks of the ophiolitic belt preserve a magmatic record critical for reconstructing Palaeozoic subduction processes. This study reports integrated geochronological and geochemical analyses of arc‐related intrusives from the Gongpoquan–Hanshan arc. Zircon U–Pb dating constrains two magmatic episodes: Middle Silurian hornblende gabbros (430.2 ± 3.5 Ma) and quartz diorites (426.6 ± 3.5 Ma), and Early Devonian syenogranites (407.4 ± 2.2 Ma). The quartz diorites exhibit typical arc magmatism signatures, including pronounced Nb–Ta depletion, high Sr contents (400–587 ppm), and steep rare earth element (REE) fractionation patterns ([La/Yb] N = 16.43–20.01). In contrast, certain Middle–Late Silurian (435–423 Ma) intrusive rocks in the region display geochemical affinities with sanukitoids or adakites. In addition, the Early Devonian (415–395 Ma) granites exhibit pronounced depletions in Nb, Ta, P, and Ti, displaying geochemical signatures typical of arc‐related magmatism. Most samples show positive ε Hf ( t ) values, suggesting a predominantly juvenile crustal source. Furthermore, a dioritic porphyry into the Xichangjing ophiolite yields a crystallisation age of 411.1 ± 2.9 Ma, indicating that the ocean basin represented by the Hongliuhe–Xichangjing ophiolite had closed by the Early Devonian. Based on the findings of this study and previous data, we propose a revised model for the Palaeozoic tectonic evolution of the central Beishan Orogenic Belt.