| Summary: | Zircon U-Pb ages from glacial clasts in Quaternary tills of the central Transantarctic Mountains indicate the presence of Grenville-age crust along the Ross Sea margin of East Antarctica. The polymict tills contain a variety of igneous, metaigneous, and metasedimentary clasts with Proterozoic ages not known from basement exposure. Four orthogneiss clasts have igneous ages of ∼1065-1100 Ma and Ross Orogen metamorphic overgrowths of ∼500-550 Ma. The latter ages indicate that these clasts are not glacially far traveled. Grenville-like signatures also come from a paragneiss containing detrital zircons ranging from 925 to 1130 Ma, an early Ross granitoid (∼563 Ma) containing inherited zircons of ∼1020 Ma, and detrital zircons from Neogene and Quaternary glacial deposits with a composite age peak of ∼1045 Ma. Other igneous clasts with ages of ∼1460, ∼1580, and ∼1880 Ma provide further evidence of Proterozoic crust and corroborate earlier finding of an ∼1440-Ma A-type granite clast with isotopic signatures matching similar-age granites in Laurentia. Together, the glacial clasts indicate that ∼1.1-Ga Grenville-age igneous crust lies beneath the ice sheet along the Ross Sea margin of East Antarctica. The clast ages are similar to those of Mesoproterozoic relicts in other parts of East Antarctica, and they resemble the ages of basement rocks in western Laurentia, including igneous rocks in west Texas (1070-1120 Ma) where the Grenville Orogen (sensu stricto) terminates abruptly, or, alternatively, metamorphic assemblages within Proterozoic rift-margin strata of northern Idaho (1000-1150 Ma). The glacial clasts provide new evidence that an ∼1.1-Ga-age belt extends from western Laurentia into central East Antarctica inboard of the present-day Pacific margin, supporting both the SWEAT (southwest U.S.-East Antarctic) fit of Rodinia cratons and the suggestion that a Mesoproterozoic orogen integral to Rodinia assembly crosses East Antarctica.
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