Protracted late Neoproterozic - early Palaeozoic deformation and cooling history of Sor Rondane, East Antarctica, from 40Ar/39Ar and U-Pb geochronology

40Ar/39Ar and U-Pb data from five structural domains constrain the late Neoproterozoic - early Palaeozoic tectonothermal history of the eastern part of the East African-Antarctic Orogen in Sor Rondane. A total of 27 new Ar/Ar ages span 570-474 Ma, roughly corresponding to the age range of three generations of syn- to post-tectonic granitoids. The ages are distinct for the five structural domains. The oldest cooling ages come from the weakly deformed southern part of the SW Terrane of Sor Rondane (SW Terrane S), a sliver of a Tonian island arc, which escaped much of the late Neoproterozoic accretionary deformation. This terrane was intruded by the oldest and largest granitoid complex at c. 640-620 Ma. The oldest Ar/Ar amphibole and biotite ages of 570-524 Ma are from the Main Shear Zone, along the northern margin of the SW Terrane S sliver. It hosts granites of age c. 584-570 Ma strung out along the shear zone. Two younger granitoid phases are recorded in the adjacent four terranes to the west, north and east of the SW Terrane S, and correlate with the younger group of Ar/Ar biotite ages spanning 513-474 Ma. We interpret the magmatic and cooling history of duration > 150 Ma to reflect repeated phases of accretion, magmatism and reactivation, that is, collage-style tectonism, partly pre-dating the incorporation of Sor Rondane into Gondwana. The study area first accreted to the cryptic Valkyrie Craton in Tonian times, was then 'sandwiched' between the Kalahari and Indo-Antarctica cratons, and experienced extensional tectonics and elevated heat flux due to lithospheric delamination, which resulted in slow cooling during the Pan-African Orogeny.

Automated summary

The 40Ar/39Ar and U-Pb data from five structural domains in the Eastern part of the East African-Antarctic Orogen in Sor Rondane provide constraints on the late Neoproterozoic - early Paleozoic tectonothermal history. Different age ranges were identified for the five structural domains, indicating distinct magmatic and cooling histories within the region. The study suggests a complex tectonic evolution involving accretion, magmatism and reactivation, predating the incorporation of Sor Rondane into Gondwana.