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Dating the closure of the Paleo-Asian Ocean (PAO) is critical to our understanding of East Asian tectonics during the formation of Pangea, yet existing estimates differ by up to 130 Myr (380 Ma to 250 Ma). We report two robust paleomagnetic results from 320-280 Ma volcanic strata in the South Mongolia-Xing’an Belt. Stable characteristic remanences of both results are likely primary and characterized by positive fold tests, consistent polarity with the Kiaman Superchron (∼318-262 Ma) and average paleosecular variation. The new results indicate that the northward motion of North China and Mongolia paralleled Laurussia from the Late Carboniferous to Early Permian. The N-S width of the PAO in the east-central segment (reference site: 43°N/114°E) was ca. 2700 km during the Late Carboniferous to Early Permian. This wide ocean impeded floral and faunal exchange until the Guadalupian, prior to its final closure by ca. 250 Ma.