Subduction initiation of the Paleo-Asian Ocean: New insights from metamorphic sole and supra-subduction zone ophiolite in central Jilin Province, northeastern China

The subduction of the Paleo-Asian Ocean played a key role in the formation of the Central Asian orogenic belt. The timing and mechanism of the subduction initiation of the Paleo-Asian Ocean remain controversial. This study presents new geochronological, mineral chemistry, whole-rock geochemical, and Sr-Nd-Pb-Hf-O isotopic data for late Cambrian metaigneous rocks from central Jilin Province, northeast China, aimed at providing pressure-temperature conditions and petrogenesis constraints for subduction initiation of the Paleo-Asian Ocean. The metaigneous rocks, composed of amphibolites and metagabbros, are collected from the Shitoukoumen and Qincaigou regions, respectively, and they yield zircon 206Pb/238U ages of ca. 503 and 502 Ma. The amphibolites from the Shitoukoumen region were divided into type 1 and type 2 based on their geochemical characteristics. Type-1 amphibolites exhibit normal mid-ocean-ridge basalt (N-MORB)−like compositions with (La/Yb)N values of 0.74−0.84, lower Th/Nb values of 0.03−0.07, a whole-rock εNd(t) value of +8.28, zircon εHf(t) values of +13.85 to +15.44, and zircon δ18O values of +0.15‰ to +2.61‰. The results reveal that the protoliths of type 1 had N-MORB affinities and were high-temperature altered oceanic crust that underwent seawater interaction. The U-Pb dating results of titanites from type 1 indicate that the amphibolite facies metamorphism occurred at 501−497 Ma. Type-2 amphibolites and Qincaigou metagabbros are characterized by supra-subduction zone (SSZ)−type compositions, featuring relatively lower (La/Yb)N values of 0.22−0.42, higher Th/Nb values of 0.03−0.58, whole-rock εNd(t) values of +5.92 to +7.90, and initial 208Pb/204Pb values of 38.162−38.193. The compositions of type 2 are indicative of a derivation from the depleted asthenospheric mantle that underwent prior metasomatism by subduction-related fluids. The geochemical characteristics of type 2 and metagabbros resemble those of SSZ ophiolite. Phase equilibrium modeling and geothermobarometry for both types of amphibolites yielded a temperature range of 606−715 °C (with some titanites and rutiles yielding temperatures of 741−791 °C) at 2.4−8.8 kbar. These conditions are consistent with low-temperature(−high-temperature) soles, reflecting high-temperature metamorphism. Combining these results with previous research, we conclude that central Jilin Province presents late Cambrian metamorphic soles and SSZ ophiolites, which record the subduction initiation of an intraoceanic arc close to a mid-ocean ridge. Our model further confirms that induced subduction, driven by the collision between microcontinental blocks and plates, was the dominant mechanism for the subduction initiation of the Paleo-Asian Ocean. This finding provides new insights into the formation of similar metamorphic soles and ophiolites worldwide.