Structure and Evolution of the Davis and Obruchev Archaean Terranes Based on the First Comprehensive Isotopic-Geochronological Studies of the Denman Glacier Region (East Antarctica)

The research into a difficult-to-reach region of Antarctica in a mountain frame of the Denman Glacier has revealed the presence of Paleoarchean and Neoarchean granite-gneiss blocks comparable to other protocratons of East Antarctica and the Earth as a whole, which is particularly relevant in the context of problems of Archean geodynamics and determining the evolutionary stages of the early continental crust. The results of U–Pb geochronological dating and Sm–Nd isotope systematics of a wide range of rocks of two Archean domains and tectonically framing fragments of the mobile belts are presented. The Paleoarchean age (3276.6 ± 29 Ma) of tonalitic gneiss protoliths in the Davis Terrane has been confirmed. For the first time, sillimanite-garnet paragneisses were identified within the terrane on Cape Charcot, with the maximum sedimentation age of their protolith dated to 3166 ± 21 Ma. Rifting of the crust in the range of 2960–2800 Ma is confirmed by metamorphic rims of zircons in gneisses and crystalline schists aged 2956 ± 21, 2870 ± 21 Ma, respectively. The consolidation of the Davis Protocraton occurred at the Mesoarchean-Neoarchean boundary, and the final stage of formation reflected in Pan-African thermal processes 545–487 Ma ago. The early stage of the Obruchev Neoarchean Terrane formation, first recorded on the Cape Jones, is associated with the crystallization of orthogneiss protoliths 2711 ± 8.9 Ma ago. Tectono-thermal events of the accretionary-collisional regime are constrained to the interval of 1190–1140 Ma, corresponding to the development of the Wilkes Mobile Belt, which correlates with the Albany-Fraser Orogeny in Australia. The ancient Davis and Obruchev protocratons developed independently of each other at the Archean-Mesoproterozoic stage of geodynamic evolution. The amalgamation of the Davis and Obruchev domains into a collage was associated with the final stage of the Rayner orogeny and the integration of Antarctica into the Rodinia supercontinent 1150–900 Ma ago.