Paper No. 120-9
Presentation Time: 10:40 AM
AGE AND ISOTOPIC CONSTRAINTS FOR THE PROTEROZOIC EVOLUTION OF CENTRAL EAST ANTARCTICA AND RELATIONSHIP TO AUSTRALIA AND LAURENTIA IN THE COLUMBIA AND RODINIA SUPERCONTINENTS
Rock clasts entrained in glacial deposits sourced from the ice-covered continental interior of East Antarctica provide a unique way to evaluate its age and composition. Zircon U-Pb ages from a large suite of granitoid clasts collected in glacial catchments draining central East Antarctica through the Transantarctic Mountains show that crust in this region was formed by a series of magmatic events at ~2.01, 1.88-1.85, ~1.79, ~1.57, 1.50-1.41, and 1.20-1.06 Ga. The dominant granitoid populations are ca. 1.85, 1.45 and 1.20-1.06 Ga. None of these igneous ages are known from the limited outcrop in the region. In addition to defining a previously unrecognized geologic history, zircon O and Hf isotopic compositions from this suite have: (1) mantle-like δ18O signatures of about 4.0-4.5 ‰ and near-chondritic Hf-isotope compositions (εHf ~ +1.5) for granitoids of ~2.0 Ga age; (2) mostly crustal δ18O (6.0 to 8.5 ‰) and variable Hf-isotope compositions (εHf = -6 to +5) in rocks with ages of ~1.88-1.85, ~1.79 and ~1.57 Ga, and in which the ~1.88-1.79 Ga granitoids require some involvement of older crust; (3) mostly juvenile isotopic signatures with low, mantle-like δ18O (about 4-5 ‰) and radiogenic Hf-isotope signatures (εHf = +6 to +10) in rocks of 1.50-1.41 Ga age, with some showing crustal sources or evidence of alteration; and (4) mixed crustal and mantle δ18O signatures (about 6.0 and 7.5 ‰) and radiogenic Hf isotopes (εHf = +3 to +4) in rocks of ~1.2 Ga age. Together, these age and isotopic data indicate the presence in cratonic East Antarctica of a large, composite igneous province that formed through a punctuated sequence of relatively juvenile Proterozoic magmatic events. Further, they provide direct geologic support for correlation of crust in East Antarctica with both the Gawler Craton of present-day Australia and Proterozoic provinces in southwestern Laurentia. Prominent clast ages of ~2.0, 1.85, 1.57 and 1.45 Ga, together with sediment source linkages between East Antarctica, Australia, and Laurentia, provide evidence for the temporal and spatial association of these cratonic elements in the Columbia supercontinent. Abundant ~1.2-1.1 Ga igneous and metamorphic clasts may indicate the presence of a Mesoproterozoic orogenic belt in the interior of East Antarctica that formed during final assembly of Rodinia.