Zircon xenocrysts in the Yushu gabbro reveal Archean basement beneath the Northern Qiangtang Block in central Tibet

Abstract The nature of the basement beneath the Northern Qiangtang Block (NQ) in central Tibet remains poorly constrained owing to the widespread Phanerozoic sedimentary cover and limited exposed basement rocks. In this study, we present U–Pb geochronological, trace-element, and Hf isotopic data for zircon xenocrysts recovered from the Yushu gabbro, with the aim of probing the hidden deep crust. The zircon xenocrysts yield two distinct age populations: igneous cores at ca. 2.53 Ga and overgrowth rims at ca. 2.43–2.46 Ga. The cores exhibit high ε Hf (t) values and relatively young Hf model ages (2.52–2.78 Ga), indicating significant juvenile crustal growth or mantle-derived magmatism during the Neoarchean. The rims, which are bright in CL images and show elevated (Sm/La) N and Ce/Ce* ratios, are interpreted as products of magmatic regrowth associated with a separate Paleoproterozoic event. These findings, together with previously reported detrital zircon age peaks at ca. 2.5 Ga from the NQ, provide supporting evidence for the existence of Neoarchean crustal components within or beneath the NQ. Our study demonstrates that zircon xenocrysts in mafic magmas serve as powerful proxies for deciphering the composition and evolution of concealed continental basement.