Microcontinental collision in the East Gondwana orogen: Evidence from geology, geochemistry, and geochronology of the collision boundary “Berrnabbane” in the Lützow-Holm Complex, East Antarctica

This study focuses on the unexplored outcrop “Berrnabbane” in the western Lützow-Holm Complex, eastern Dronning Maud Land within East Gondwana orogen. Various protolith ages are identified from the small outcrop, which can be considered as small-scale analogs of the extensive Lützow-Holm Complex. These rocks with different protolith ages are in contact with each other without obvious shear zones. The central to the southern part is composed of felsic gneiss with a protolith age of 2.5 Ga. These rocks are derived from a microcontinent formed by slab melting in an initial island arc tectonic setting. The central Berrnabbane includes felsic gneiss and mafic granulite with a protolith age of 1.9 Ga. These rocks are enclosed within pelitic gneiss, with a maximum depositional age of 1.8 Ga. These rocks correspond to the continental margin arc, including an accretionary prism developed around the 2.5 Ga microcontinental margin. The northern part comprises felsic gneiss with a protolith age of 1.0 Ga, which originated from another juvenile continent. The duration of metamorphism differs between rocks with the 2.5 Ga (with 1.9–1.8 Ga reworked margin) and the 1.0 Ga continents. Both share the event during 550–500 Ma, whereas only the 2.5 Ga continent preserves former thermal events from ∼ 600 Ma. The earlier event might be the crustal thickening caused by the collision and burial of the 2.5 Ga microcontinent beneath the 1.0 Ga continent, and the latter event should be a cratonic collision known as the Kuunga Orogeny. The prolonged orogenesis preserved only in the 2.5 Ga microcontinent suggests that radiogenic heat production would play an important role in extremely high-temperature metamorphism in the East Gondwana orogeny. The present results indicate that the Lützow-Holm Complex correlates more closely with the Sri Lankan Complexes than with other complexes in Dronning Maud Land during the amalgamation of Gondwana.