Recognition of Pan-African-aged metamorphism in the Fisher Terrane, central Prince Charles Mountains, East Antarctica

The Fisher Terrane, located in the central region of the Prince Charles Mountains, provides key data regarding the evolution of the East Antarctic Shield. Our study provides evidence that the Fisher Terrane formed in proximity to a Proterozoic plate boundary and was subsequently metamorphosed during the late Neoproterozoic to early Cambrian during the final stages of Gondwana amalgamation. U–Pb detrital zircon geochronology reveals that metasedimentary from Fisher Massif were deposited after c. 1300 Ma, and contain detritus derived from the Rayner–Eastern Ghats Terrane. This suggests that the Fisher Terrane was not an isolated oceanic arc but rather formed on the same tectonic plate as the Rayner Complex. Metapelitic schists from within the same metasedimentary package yield metamorphic U–Pb monazite ages of c. 512–509 Ma, corresponding to a regionally recognised Pan-African-aged event. This event has not been previously identified in the Fisher Terrane, and demonstrates that Pan-African-aged metamorphism affected all parts of the Prince Charles Mountains. Calculated phase equilibria modelling constrains the metamorphic conditions during this event to 2.5–4.0 kbar and 550–615 °C, corresponding to apparent thermal gradients of 146–220 °C/kbar. Such conditions plausibly relate to metamorphism taking place in an extensional setting. Supplementary material: https://doi.org/10.6084/m9.figshare.c.4392710