The Shackleton Range (East Antarctica): an alien block at the rim of Gondwana?

The Shackleton Range is a truncated Pan-African Orogen situated at the Weddell Sea margin of East Antarctica. It almost exclusively consists of basement rocks exposed at an elevated, escarpment-bound palaeosurface and is covered locally by patchy remnants of Ordovician, Permian and, controversially, Jurassic terrestrial deposits. This inventory does not match the geological record of any other place in Antarctica. Here we reconstruct the Phanerozoic evolution of the Shackleton Range by means of a multi-disciplinary approach combining petrological, geochemical and geochronological data with thermal history models of zircon and apatite fission track (ZFT, AFT) and (U-Th-Sm)/He (AHe) data. Petrographic, geochemical and 40Ar/39Ar analyses of a sedimentary cover sequence identify volcaniclastic rocks related to the Ferrar/Karoo magmatic event. Thermal history modelling of ZFT ages of 160-215 Ma, AFT ages of 124-225 Ma, AHe ages of 95-169 Ma and kinematic proxies in combination with geological information indicates a complex thermal history comprising at least three cooling episodes interrupted by reheating pulses. Thermal history refers to inversion of part of the Carboniferous-Triassic Transantarctic Basin prior to the 180 Ma Ferrar/Karoo Event and formation of an up to 3.4 km deep extensional Jurassic - Early Cretaceous basin due to Weddell Sea rifting. Basin depth was diminished by regional middle Cretaceous stress field changes. Final basin inversion and surface uplift were likely triggered by far-field tectonics and climatic influence. This history represents a typical example for the transition from an active to passive margin setting along the outer rim of Gondwana.