Paleozoic Long-Term Subduction in the Beishan Orogen: Evidence from Early Cambrian and Early Permian Gabbros of Jijitaizi Area

Abstract

The prolonged subduction history of the Palaeo-Asian Ocean remains pivotal to reconstructing the accretion history of the Central Asian Orogenic Belt, yet its duration and tectonic evolution are debated due to ambiguous ophiolite records. Here, we identified Early Cambrian and Early Permian gabbros in the Jijitaizi ophiolite of the Beishan orogen, obtaining zircon U-Pb ages of 514 ± 3, 292 ± 3 and 289 ± 2 Ma. Early Cambrian gabbros exhibit back-arc basin affinities: N-MORB-like REE patterns (∑REE = 22.55–30.11 ppm) with subduction-fluid imprints (Th/Ta > 1 and negative Nb anomalies), indicating derivation from depleted MORB mantle metasomatised by slab fluids. Early Permian gabbros show ultra-depleted forearc cumulate signatures: extreme REE depletion (∑REE = 3.48–4.81 ppm), high ε_Nd(t) (+10.49 to +14.07), low Ti/V (4.62–6.08), high Ca^# and anorthitic plagioclase (An_80–93). The regional data collectively constrain the Jijitaizi–Xiaohuangshan and Hongliuhe–Xichangjing ophiolites as a unified back-arc system in the Early Cambrian, also providing evidence for long-term subduction from Early Cambrian to Early Permian.

Keywords

gabbro / Jijitaizi ophiolite / Paleozoic / subduction / the Beishan orogen

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2026 Geological Society of China.