Several lines of evidence suggest that the Earth's tectonic regime might have undergone a significant change in the period of 3.2-2.8 Ga. Investigations of Archean terrains that may have recorded such shift can help better understand Earth`s tectono-thermal evolution. The Saglek-Hebron complex (SHC) in Northern Labrador, located on the westernmost margin of the North Atlantic Craton, is one of the oldest records of continental crustal rocks with rocks as old as nearly 3.9 Ga. It mainly consists of Archean TTG gneiss formed within the entire Archean Eon, and includes two supracrustal suites (Eoarchean Nulliak and Paleoarchean Upernavik). It was suggested that the SHC has experienced multiple magmatic-metamorphic events from ca. 3.87 Ga to ca. 2.5 Ga or even younger. These tectono-thermal events and associated geodynamic processes are significant for us to understand the early Earth lithospheric evolution and the ongoing tectonic mode. Here, we investigate a metasedimentary rock from the Eoarchean Nulliak supracrustal unit. The sample is composed of garnet + orthopyroxene (Al2O3 of ~8 wt%) + quartz + antiperthite + rutile, interpreted to have formed during the peak metamorphic stage. A combined application of two-feldspar-thermometry, Zr-in-rutile thermometry, as well as mineral mode and chemical composition isopleth by phase equilibria modelling, allowed identifying the occurrence of ultrahigh-temperature (UHT) metamorphism with a peak temperature above 900 ℃ and a pressure of 7.4-9 kbar and post-peak near isobaric cooling (IBC) retrogression evolution characterized by the formation of retrograde biotite and fibrous sillimanite. Secondary Ion Mass Spectroscopy (SIMS) data revealed that detrital zircon grains show a wide range of ages from ca. 3.6 Ga to ca. 2.9 Ga, while metamorphic zircon grains yield 207Pb/206Pb ages ranging from 2705 Ma to 2752 Ma, defining a weighted mean age of 2728 ± 6.3 Ma. Our study shows that the SHC Nulliak supracrustal assemblage recorded a single episode of Neoarchean UHT metamorphism with a short-lived duration of < 40 Myr, combined with the results of Ti-in-zircon thermometry. UHT metamorphism worldwide occurs in clusters at 2800–2500 Ma, 2100–1500 Ma, 1200–1000 Ma, 650–540 Ma, and 100–0 Ma, and correlates with the amalgamation of supercratons and supercontinent cycles. Its generation is closely related to the evolution of plate tectonics, especially the convergent margin tectonic processes. Comparing with the other well-studied Archean UHT metamorphic rocks, and as tectonic thickening and radiogenic heating alone are not sufficient to cause such short-lived UHT metamorphism, we conclude that the formation mechanism of UHT metamorphism in the SHC might be caused by the lithospheric thinning and the associated asthenospheric upwelling during the lithospheric peeling in a thinned orogen.