The Gondwana Plate margin in the Weddell Sea sector: Zircon geochronology of Upper Paleozoic (mainly Permian) strata from the Ellsworth Mountains and eastern Ellsworth Land, Antarctica

Abstract

Zircon geochronology has been applied to upper Paleozoic (mainly Permian) strata from the Ellsworth Mountains and from enigmatic outcrops in eastern Ellsworth Land to aid in constraining their locations in the Weddell Sea sector of the Gondwana plate margin. Detrital zircons from two Polarstar Formation (Ellsworth Mountains) sandstones yielded maximum depositional ages of ~270Ma and ~260Ma. Detrital zircons from Permian beds at Erehwon Nunatak and beds of uncertain age at FitzGerald Bluffs, both in eastern Ellsworth Land, gave maximum depositional ages of ~264Ma and ~525Ma respectively. Two Polarstar Formation tuffs gave ages of 258.0±2.1Ma and 262.6±2.2Ma. The Polarstar Formation probably spans the entire Permian. The quartzite at FitzGerald Bluffs is comparable in composition and detrital zircon signature to Devonian sandstones in both the Ellsworth and Transantarctic Mountains. Evaluation of the Polarstar Formation with respect to Permian strata in the southern Karoo and Falkland Islands suggests deposition in a separate and distinct basin, which was related to that in the Transantarctic Mountains. A separate depositional basin forms an additional constraint on the location of the Ellsworth-Whitmore block adjacent to the Coats Land/Pensacola Mountains region. The eastern Ellsworth Land outcrops are inferred to document a small continental block located proximal to the Ellsworth-Whitmore Mountains block during Gondwana time.