Palaeoproterozoic to Palaeozoic magmatic and metamorphic events in the Shackleton Range, East Antarctica: Constraints from zircon and monazite dating, and implications for the amalgamation of Gondwana

A comprehensive set of new geochronological data from different parts of the Shackleton Range in East Antarctica, comprising U–Pb single zircon and Th–U–Pb single and multi-grain monazite data, combined with published results, reveal a complex tectono-thermal history of the Shackleton Range. Three distinct, spatially separated terranes or units with different magmatic and metamorphic history are now recognised: (i) the Southern Terrane (Unit I) contains detrital components as old as 2850 Ma, experienced magmatism between 1850Ma and 1810Ma and underwent amedium- to high-grade metamorphic event at 1710–1680Ma and, locally, again at 510 Ma; (ii) the Eastern Terrane (Unit II) occurs in the easternmost part of the Shackleton Range and contains c. 1060Ma old Grenvillian granitoids, which experienced metamorphism at c. 600 Ma; and (iii) the Northern Terrane (Unit III) is characterised by 530Ma old granites and diorites, which are hosted within paragneisses as well as mafic and ultramafic rocks. All rocks of Unit III experienced upper amphibolite- to granulite-facies and, locally, eclogite-facies metamorphism at 510–500 Ma. The geologic features of Palaeoproterozoic tectonism in the Southern Terrane are very similar to those of the Australo-AntarcticMawson Continent. Thismay indicate that theMawson Continent extends across the East Antarctic Shield into the Shackleton Range. The 1060Ma and 600Ma events in the Eastern Terrane have not been documented for any part of the Shackleton Range before and are correlated with Grenvillian and Pan-African tectonism in Dronning Maud Land. By implication, this suggests that the Pan- African Mozambique/Maud Belt continues into the Shackleton Range. The associated suture is located in the easternmost Shackleton Range and is related to the amalgamation of the Indo-Antarctic plate with West Gondwana. This was followed by further collision of the combined Indo-Antarctic/West Gondwanan block with East Gondwana at approximately 510Ma in theNorthern Terrane. A suture related to this latter collision can be traced in the Northern Shackleton Range and may continue northwards to the Sør Rondane Mountains and the Lützow Holm Bay area. Our data support the model that East Antarctica finally assembled during the Pan-African orogeny, rather than during earlier Mesoproterozoic events.

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