Provenance and age constraints of Paleozoic siliciclastic rocks from the Ellsworth Mountains in West Antarctica, as determined by detrital zircon geochronology
New SHRIMP U-Pb detrital zircon ages from Cambrian to Permo-Carboniferous siliciclastic units in the Ellsworth Mountains constrain provenance and maximum depositional age, as well as providing key information as to the tectonic evolution of a problematic region. The Cambrian Heritage Group was deposited during an active continental rift setting and has main zircon components of late Mesoproterozoic-early Neoproterozoic age (ca. 1300-900 Ma) with little to no contributions from older cratons. Two meta-volcaniclastic samples of the Union Glacier Formation (lower Heritage Group) have U-Pb zircon ages of ca. 675 Ma indicating proximal Cryogenian volcanism, thereby raising questions as to the depositional age of this unit. Igneous and metamorphic zircons of late Neoproterozoic-early Cambrian age (650-530 Ma) are a secondary component, present in the upper part of this group. The passive margin sediments of the overlying Upper Cambrian-Devonian Crashsite Group record an upsequence increase in late Neoproterozoic-Cambrian detrital zircons (ca. 650-480 Ma). The youngest detrital zircons were dated at ca. 480 Ma and major peaks at ca. 530 and 500 Ma. Similar patterns are recorded in the Permo-Carboniferous Whiteout Conglomerate, with main components at ca. 650-500 Ma, and an absence of detrital zircons younger than Cambrian. The results, combined with stratigraphic constraints, suggest that sediments of the lower Heritage Group were derived from the paleo-Pacific margin of the Australo-Antarctic plate. Cryogenian igneous zircon ages from the Union Glacier Formation indicate proximal rift-related magmatism, previously only recognized in the Transantarctic Mountains, and are interpreted to relate to the breakup of Rodinia. Sediments from the upper Heritage Group were derived from proximal sources, likely in Coats Land and Dronning Maud Land, with possible extensions into the Shackleton Range. This area was probably uplifted during the final amalgamation of Gondwana, which restricted the supply of sediment from older cratons. Sediments from the Crashsite Group allow for a more expansive source region that could be located in Dronning Maud Land, the Shackleton Range, the Tansantarctic Mountains and Southern Africa. Sediments of the Whiteout Conglomerate, together with comparisons with other coeval glaciogenic strata, indicate that deposition during the Permo-Carboniferous was similar to that in the Transantarctic Mountains. Our data support that the Ellsworth-Whitmore Mountains crustal block was once part of the Australo-Antarctic plate rather than the southern African sector.
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|GEOLOGICAL SOCIETY OF AMERICA BULLETIN
|GEOLOGICAL SOC AMER, INC
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