Early Carboniferous Seafloor Spreading Recorded By Volcanic Rocks In The Western Segment Of The Changchun-Yanji Suture Belt, Ne China

This study reports zircon U-Pb geochronological, geochemical, and zircon Hf-O isotopic data for metavolcanic rocks from the Shitoukoumen and Yongji areas in central Jilin Province, northeast China, to reveal their petrogenesis and tectonic setting. The metavolcanic rocks collected from the Shitoukoumen and Yongji areas are composed of metabasaltic trachyandesite, metatrachyandesite, and metarhyolitic tuff. Zircon U-Pb dating results indicate that the metavolcanic rocks were erupted during 359-355 Ma. Metavolcanic rocks in the Shitoukoumen area can be divided into two groups according to their geochemical characteristics. Group-I rocks (metabasaltic trachyandesite and metatrachyandesite) show geochemical features similar to those of ocean island basalt (OIB), with slightly lower zircon delta O-18 values (4.06 +/- 0.42 parts per thousand to 5.16 +/- 0.28 parts per thousand) than those of mantle-derived zircons, and depleted epsilon(Hf)(t) values (7.84-15.4). Group-II rocks (metabasaltic andesite) show similar geochemical characteristics to those of normal mid-ocean ridge basalt (N-MORB). Group-I rocks may have been derived from partial melting of enriched mantle involving high-temperature altered oceanic crust, whereas Group-II rocks originated mainly from partial melting of depleted mantle. Metarhyolitic tuffs from the Yongji area have high SiO2 and K2O contents, as well as high Ga/Al ratios, and show similar geochemical characteristics to those of A-type rhyolites. The results of the study, together with published data, indicate that the eastern segment of the northern margin of the North China Craton was a passive continental margin setting during the early Carboniferous, and that the Paleo-Asian Ocean remained open along the Changchun-Yanji suture belt until the early Carboniferous.