Zircon U-Pb dating and P-T constraints on the Mesoproterozoic-Neoproterozoic metamorphic evolution in the southwestern Prydz Bay sector, East Antarctica

New petrographic, geochemical, thermobarometric, and SHRIMP U-Pb zircon data are presented for three outcrops of metaigneous rocks (felsic gneiss and mafic granulites) from the southwestern Prydz Bay sector of East Antarctica. Their magmatic protolith ages range from the late Mesoproterozoic to the early Neoproterozoic (1129 Ma±4 Ma, 1104 Ma±12 Ma, and ca. 1080 Ma). Geochemical data indicate that the felsic gneiss protolith was derived from a high-pressure, arc-related granitoid melt source, whereas the mafic granulites preserve characteristics of mafic igneous rocks formed within an evolving arc-back-arc system along the Rayner active margin. Zircon records a polyphase Rayner-age metamorphic history, including an early high-temperature to locally ultrahigh-temperature stage at ca. 1010-970 Ma and a regional granulite-facies event at ca. 890 Ma. Peak conditions during the early stage reached ca. 850-935 ℃ at variable middle-crustal pressures of ca. 3-7 kbar, whereas the ca. 890 Ma event and associated retrograde re-equilibration were mainly recorded at ca. 740-850 ℃ and ca. 3.0-5.7 kbar. Zircon trace-element compositions reveal melt- and fluid-assisted recrystallization, demonstrating that Th/U ratios alone are unreliable for distinguishing magmatic from metamorphic zircon in granulite-facies rocks. The data obtained, together with subglacial drilling results, are consistent with regional interpretations of the Rayner Province as a late Mesoproterozoic-early Neoproterozoic arc-back-arc crustal system. No robust Cambrian zircon populations were identified, suggesting limited Pan-African reworking west of the Larsemann Hills.