Paper No. 12
Presentation Time: 4:10 PM
ARCHEAN, PALEOPROTEROZOIC AND MESOPROTEROZOIC CRUST OF CENTRAL EAST ANTARCTICA: NEW INSIGHTS ON SUBGLACIAL GEOLOGY STRENGTHEN RODINIA TIES TO WESTERN LAURENTIA
New U-Pb zircon ages from a large suite of granitoid clasts collected from glacial catchments draining central East Antarctica show that the crust in this ice-covered region was formed by a series of magmatic events at 2.01, 1.88-1.79, 1.57, 1.48-1.43, and 1.22-1.06 Ga. The dominant granitoid populations are 1.88, 1.46 and 1.06 Ga, with some metamorphic overprinting at 1.18-1.15 Ga. Zircon Hf and O isotopic compositions from this suite have: (1) near-chondritic εHf compositions (-2 to +3) and mantle-like δ18O for granitoids of ~2.0 Ga age; (2) variable compositions with εHf = -7 to +5 and mostly crustal δ18O in rocks with ages of ~1.88-1.85, ~1.79 and ~1.57 Ga, and the ~1.88-1.79 Ga granitoids require some involvement of older crust; (3) mostly juvenile isotopic signatures with εHf = +5 to +12 and low, mantle-like δ18O in rocks of 1.50-1.45 Ga age, with some showing crustal sources or evidence of alteration; and (4) mixed crustal and mantle δ18O signatures and εHf = +2 to +6 in rocks of ~1.2 Ga age. Together, these age and isotopic data provide the first glimpse of crustal growth history in central East Antarctica and suggest a punctuated history of relatively juvenile Proterozoic magmatism. None of these igneous ages are known from limited Antarctic outcrop in the region, including magmatic ages of ~3.1, 2.5 and 1.7 Ga in the Nimrod Group, yet these ages and isotopic compositions resemble those documented from western Laurentia. Detrital zircon ages from Paleoproterozoic metaquartzites yield discrete populations of 3.1, 2.5, 2.0, 1.7, 1.4 and 1.2 Ga, strengthening the case for episodic magmatic growth of East Antarctic crust. Together, the basement and clast ages indicate the presence in central East Antarctica of a large, composite Archean-Proterozoic craton that reflects crustal growth within the core of East Gondwana. Age and isotopic correlation of 1.85, 1.46 and 1.21 Ga East Antarctic crust with comparable provinces in Laurentia (Idaho-Medicine Hat, Yavapai-Mazatzal-granite, and Grenville-Mojave, respectively) provide direct geologic support for the SWEAT reconstruction of Rodinia. Abundant ~1.2-1.1 Ga igneous and metamorphic clasts indicate the presence of Grenvillian orogenic belts in the interior that may record Rodinia assembly.