Detrital zircons from upper Permian and lower Triassic Victoria Group sandstones, Shackleton Glacier region, Antarctica: Evidence for multiple sources along the Gondwana plate margin

In the central Transantarctic Mountains region, siliciclastic strata of the Permian-Triassic Victoria Group (Beacon Supergroup), the Gondwana sequence in Antarctica, have both cratonic and magmatic arc provenance. Volcaniclastic strata occur in the upper part of the Permian Buckley Formation, whereas the Triassic Fremouw and Falla formations are more quartzose. Two sandstones in the upper Buckley and one near the base of the Fremouw, and immediately above the Permo-Triassic boundary, in the Shackleton Glacier region have yielded detrital zircon U/Pb SHRIMP age populations with clear evidence for a contemporaneous source. The stratigraphically lowest sample, about 70 m below the top of the Buckley Formation, is dominated by zoned igneous zircons of late Permian age. The sample from near the top of the Buckley Formation, about 40 m below the Permo-Triassic boundary, predominantly has zoned igneous zircons with the principal age peak again late Permian but with subordinate Devonian and Cambrian age peaks. The third sandstone from just above the Permo-Triassic boundary yielded zircons mainly of Neoproterozoic to Cambrian age. These results indicate a Permian-Triassic magmatic source existed during upper Buckley time, which is consistent with paleocurrent indicators of flow from the West Antarctic flank of the Permian-Triassic foreland basin, the inferred plate margin (Panthalassan) flank. The Devonian source is attributed to the Ford granodiorite suite in Marie Byrd Land, West Antarctica. Because Beacon strata cover the Cambrian Ross orogen and extend onto older basement, the Cambrian and Upper Proterozoic zircons are interpreted to be reworked from sandstones (Ordovician, Devonian, Early Permian in age) exposed in the Permian-Triassic Gondwanide orogen as a result of uplift of a fold and thrust belt by late Permian time.