Reconstruction of the early Mesozoic plate margin of Gondwana by U–Pb ages of detrital zircons from northern Victoria Land, Antarctica

Abstract

Abstract Detrital zircons of eight sandstone samples from the Triassic–Early Jurassic Section Peak Formation (Victoria Group, Beacon Supergroup) in northern Victoria Land, Antarctica, were investigated by U–Pb LA–ICPMS dating. The basin was flanked by the East Antarctic craton, and by a magmatic arc at the palaeo-Pacific margin of Gondwana. It accommodated sandstones ranging from quartzo-feldspathic to volcaniclastic in composition. The detrital zircon age spectra yield pronounced concentrations at c. 190–250 Ma, 500–700 Ma and 800–1200 Ma. The proportion of Triassic–Early Jurassic zircons increases from base to top of the formation, and correlates positively with the abundance of detrital volcanic rock fragments. The youngest zircon ages are close to the stratigraphic age of each sample, indicating contemporaneous magmatic activity along the active margin of Gondwana. Igneous rocks that formed during the Ross Orogeny ( c. 470–545 Ma) were a minor source only, suggesting that the Ross Orogen became progressively covered by sediments as the basin expanded. Pan-African ( c. 500–700 Ma) and Grenville ( c. 800–1200 Ma) age zircons may have been derived from crustal sources currently covered beneath the polar ice sheet, although recycling from Cambro-Ordovician units provides an alternative explanation. Supplementary material: The exact results of the age analyses of all samples are presented in Tables A1 to A8 at www.geolsoc.org.uk/SUP18624