Reconnaissance SHRIMP U-Pb zircon dating of 90 samples from the Early Proterozoic Nagssugtoqidian orogen of West Greenland, together with previous age and isotope data as well as new field observations, yields information on some large-scale structures of the orogen: 1900–1940 Ma dioritic to tonalitic juvenile arc rocks (positive initial ϵNd values) are thrust more than 50 km over Archean gneisses in the central and northern portions of the orogen. Archean and Proterozoic rocks are tectonically interleaved near the southern margin of the orogen. Regional reworking (high-grade metamorphism, shearing, and crustal melting) occurred at 1800–1840 Ma and ca. 1780 Ma. Tectonic emplacement of juvenile Proterozoic arc rocks over Archean gneisses suggests that the Nagssugtoqidian orogen contains slices of unrelated rocks swept together by closure of an ocean of unknown extent.