Abstract
The subduction history of the Hongshishan Ocean within the Beishan orogenic collage is crucial to our understanding of the evolutionary mechanisms of the Palaeo-Asian Ocean. We describe the petrography, age and geochemistry of an Ordovician–Carboniferous volcano-sedimentary succession that provides a record of the subduction history of the Hongshishan Ocean. We obtained early Ordovician zircon U–Pb ages (482 ± 6 and 472 ± 2 Ma) from the Xianshuihu Formation. The youngest weighted mean detrital zircon age from the Yuanbaoshan Formation is 421.0 ± 8.8 Ma. Most detrital zircons have prominent age peaks at 900–840 and 543–462 Ma, suggesting a main source from the southern Mongolian microcontinent. Volcanic rocks from the Baishan Formation yielded weighted mean ages of 300.3–299.3 Ma. During the Ordovician–Devonian, some volcanic arcs formed on the northern side of the Hongshishan–Baiheshan–Erlegen Ula ophiolitic belt, indicating that the Hongshishan Ocean had a northward subduction polarity. During the Carboniferous, continental arcs were well developed on both sides of the Hongshishan–Baiheshan–Erlegen Ula belt, suggesting bidirectional subduction. An archipelago of multiple arcs of the Hongshishan Ocean resembles that of the West Pacific Ocean. The change in subduction polarity can be attributed to the characteristics of multi-oceanic accretion.
Published Version
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