Distinct P–T evolution of Pan-African HT–LP metamorphism recorded by paragneisses from the Larsemann Hills, East Antarctica, and tectonic implications: Phase equilibria and geochronological constraints

Different types of paragneisses are exposed in the Larsemann Hills and adjacent region, East Antarctica. We conducted a detailed study of a sillimanite–cordierite–biotite gneiss (sample AZSZ-08) and garnet–sillimanite–biotite gneiss (sample AZSZ-09), based on petrographic observations, phase equilibria modelling, and geochronology. Both samples preserve typical high-temperature and low-pressure (HT–LP) mineral assemblages, but record different clockwise P–T paths, including near-isobaric heating in sample AZSZ-08, and cooling and decompression in sample AZSZ-09. The peak P–T conditions were 4–5 kbar/780–800 °C and ∼ 11 kbar/∼900 °C, respectively. UPb dating of zircon, monazite, and rutile in sample AZSZ-08 yielded ages concentrated in three clusters at 2697–2568, 2496–2384, and 1003–822 Ma, and a definitive metamorphic age of ca. 535 Ma. Mica RbSr dating of this sample yielded a cooling age of ca. 445 Ma. Zircon UPb dating of sample AZSZ-09 yielded detrital zircon ages concentrated at 1164–599 Ma, peak metamorphic ages of 560–540 Ma, and cooling ages of ca. 516 and 496–456 Ma. The detrital zircon age population indicates that sample AZSZ-08 was likely derived from Precambrian terranes located near the Larsemann Hills, while sample AZSZ-09 is similar to previously reported samples and has a Grenvillian protolith age. The metamorphic P–T paths and age data record Pan-African tectonothermal events that lasted for a relatively long period of time (560–450 Ma). Combined with a previous petrological study of the Prydz Belt, including determination of P–T paths and age data, the distinct P–T evolution of the HP–LP metamorphism may record processes at different crustal levels during uplift and subsequent extension in the Pan-African Orogeny.