Provenance of Contemporaneous Volcanic Zircons Preserved in the Middle Jurassic Coal of the Northern Ordos Basin, North China, and Its Implications for the Closure Timing of the Mongol‐Okhotsk Ocean

ABSTRACT The deep‐time volcanic ash preserved within coal‐bearing strata holds significant implications for reconstructing the plate tectonic history around coal‐accumulating basins and their associated resource‐environmental effects. The Middle Jurassic represents one of the major coal‐forming periods in the North China Craton (NCC). During this period, the NCC was located at the convergence of three tectonic domains: the Mongol‐Okhotsk Ocean (MOO), the Paleo‐Pacific Ocean (PPO) and the Bangong‐Nujiang Tethys Ocean (BNTO), potentially recording key geological events from these three major tectonic domains. This study presents analyses of detrital zircon U–Pb geochronology, Lu‐Hf isotopic geochemistry and whole‐rock geochemistry of Middle Jurassic coals from the Dongsheng Coalfield in northern Ordos Basin of the NCC. The detrital zircons reveal four primary age populations: Neoarchean to early Mesoproterozoic, late Mesoproterozoic to early Neoproterozoic, early Palaeozoic to early Mesozoic and Middle Jurassic. The pre‐Middle Jurassic zircons are interpreted to derive from the northern orogenic uplift of the Ordos Basin. The Middle Jurassic zircons with juvenile Hf isotopic compositions suggest a provenance from PPO subduction‐related volcanism in northeastern China. A distinct zircon subgroup exhibiting narrowly defined near‐zero ε Hf (t) values and T DM2 model ages of 1.14–1.40 Ga is inferred to be sourced from volcanic activity associated with crustal thickening after MOO closure. When synthesized with previously documented Jurassic magmatic migration patterns in the Great Xing'an Range alongside paleomagnetic and structural evidence, these findings support the view that the final closure of the MOO likely occurred around the Early–Middle Jurassic boundary.