Abstract: High-pressure granulites and orthogneisses from glacial moraines in the Grove Mountains, East Antarctica, were collected for zircon U-Pb isotope analysis. The zircon grains from four high-pressure granulites were mostly of metamorphic origin. However, some contained an inherited core aged 2633–2502 Ma. The metamorphic zircons showed two age stages (~570 Ma and ~555–545 Ma representing the earlier prograde and peak HP metamorphism ages, respectively) and displayed flat HREE patterns in the chondrite-normalized REE diagram. The zircon grains from two orthogneisses typically showed a magmatic core with oscillatory zoning and a metamorphic rim without zoning. Different protolith ages were obtained from zircon cores of these two orthogneisses. An upper intercept age of 1060 ± 40 Ma was obtained from the cores of zircon in one sample, suggesting that its protolith came from the subglacial highlands in the southeast Grove Mountains. Analytical spots from another sample yielded a protolith age of 917 ± 4 Ma, consistent with the protolith ages obtained for orthogneisses and mafic granulites that crop out in the Grove Mountains. The analytical spots from zircon rims from the two orthogneisses yielded similar metamorphic ages of ~530 Ma, in agreement with the time of retrograde metamorphism of high-pressure granulites reported previously. High-pressure granulites were common in glacial moraines from the Grove Mountains, reflecting their widespread occurrence in the subglacial highlands. Moreover, U-Pb zircon dating confirmed that the subglacial highlands of the Grove Mountains underwent a single Pan-African metamorphic cycle, but there was no evidence of a Grenville-age metamorphic event.

Key words: East Antarctica, Grove Mountains, moraines, zircon U-Pb dating, Pan-African metamorphism