CONTINUATION OF THE LAURENTIAN GRENVILLE PROVINCE IN WESTERN EAST ANTARCTICA

The positions of Laurentia and conjugate cratons in the Proterozoic supercontinent of Rodinia are controversial. What landmass rifted from Laurentia’s western margin is debated, and proposed links include East Antarctica, Australia, Siberia, and South China. Existing geologic, age and isotopic data provide a positive test of the juxtaposition between western East Antarctica and southwestern Laurentia (SWEAT hypothesis). This is further supported by new U-Pb age data from large glacial clasts and detrital zircons in Plio-Pleistocene tills of the central Transantarctic Mountains (TAM) that indicate the presence of Grenville-age igneous crust in western East Antarctica. The polymict tills contain a variety of igneous, metaigneous and metasedimentary clasts that yield Proterozoic ages previously unknown in the TAM, including ~1880, ~1580 and ~1100 Ma. Four orthogneiss clasts have igneous zircon ages of ~1100-1065 Ma. Zircon overgrowths formed during Ross Orogen metamorphism at ~500-550 Ma indicate these Mesoproterozoic clasts are not glacially far-traveled. A metasedimentary gneiss, also showing Ross overprint, contains detrital zircons ranging from 1130-925 Ma, and an early Ross granitoid (~563 Ma) contains inherited zircons of ~1020 Ma. The Grenville ages from multiple clasts are also represented by detrital zircon ages from Pliocene (Sirius Group) and Pleistocene glacial deposits with a composite age peak of ~1045 Ma. An alkali-feldspar granite clast of ~1460 Ma corroborates earlier finding of an ~1440 Ma A-type rapakivi 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 East Antarctic ice sheet proximal to the Ross Orogen. Their ages match those reported from igneous basement in west Texas (1070-1120 Ma), indicating that the Grenville Orogen (sensu stricto) extends beyond its termination in southwestern Laurentia into western East Antarctica, supporting both the SWEAT fit of Rodinia and suggestion of a Mesoproterozoic orogen crossing East Antarctica that was integral to Rodinia assembly.