Age provinces in the Antarctic craton: Evidence from detrital zircons in Permian strata from the Beardmore Glacier region, Antarctica

Abstract

The Antarctic Gondwana sequence crops out along the Transantarctic Mountains. Permian strata at Mt. Bowers and Mt. Weeks in the central part of the range were mainly derived from the ice-covered East Antarctic craton, for which the geology is inferred from coastal outcrops and the Miller Range in the Transantarctic Mountains. Analysis of detrital zircons from Permian sandstones at those two localities demonstrate a slowly changing zircon age-probability distribution for four samples from the lower part of the sequence, with an abrupt change for the upper Buckley Formation sandstone. The stratigraphically lowest sample, from a unit informally designated the Mt. Bowers sandstone, is dominated by zircons in the age range 610-540 Ma, with minor components at ∼ 1.0 Ga and ∼ 2.7 Ga. Upward, the Pagoda Formation sandstone is likewise dominated by zircons of 600-550 Ma age together with a significant Grenville-age cluster (1.3-1.0 Ga) and a minor 1.5-1.4 Ga cluster. The Fairchild Formation sandstone has a preponderance of grains in the range 600-530 Ma, with a scatter of older ages. Zircon grains in the lower Buckley Formation sandstone are principally in the range 575-520 Ma with another cluster at 470-450 Ma and a scattering of older ages. Most zircons in the upper Buckley Formation sandstone are Permian in age, but with a very small component in the range 650-475 Ma and a trace of older ages. Archean to early Mesoproterozoic zircon grains are few in number and may have been recycled from distal outcrops. The 1.5-1.4 Ga grains suggest an unexposed Mesoproterozoic source within the East Antarctic craton, which could have been linked to Laurentian North America. The Grenville-age source is considered to be, similarly, a sub-glacial belt in the interior of East Antarctica. Zircons with a late Neoproterozoic to Ordovician signature (600-460 Ma) were derived from a Ross Orogen foreland sequence, and/or an early and inland extension of the orogen itself. Permian zircons in the upper Buckley sandstone reflect the development of a magmatic arc on the Gondwana Pacific margin.