Shrimp U-Pb Ages of Zircon from Banded Gneisses and A Leucocratic Dyke in the Wilson Terrane, Northern Victoria Land, Antarctica

The Wilson Terrane is primarily composed of Precambrian-Early Palaeozoic medium-to high-grade metasedimentary rocks as well as Cambrian-Ordovician intrusive rocks, and was amalgamated with the northeastern Bowers and Robertson Bay terranes during the Ross Orogeny to form northern Victoria Land, Antarctica. In order to preliminarily constrain timing of metamorphism and provenance of the sedimentary protoliths, the U-Pb compositions of zircon from two banded gneisses and a leucocratic dyke of the Wilson Terrane were measured using a SHRIMP-IIe. Apart from Early Ordovician magmatic ages, the U-Pb age distribution of zircon is characterized by a couple of major populations at similar to 1.0-1.2 Ga and similar to 530-700 Ma correlative to the Grenville and Pan-African orogenies, respectively, with scattered ages over 1.6 Ga and the prominent early-to-middle Neoproterozoic (similar to 700-900 Ma) absence. The relatively small fraction, high Th/U ratio, and rare metamorphic texture of Early Cambrian zircon in the banded-gneiss samples suggest their youngest apparent age similar to 530 Ma as the maximum depositional age. For the leucocratic dyke, the weighted mean Pb-206/U-238 age of the oscillatory-zoned overgrowth rims of zircon is similar to 480 Ma, and apparent ages for the structureless, intermediate regions with low Th/U ratios between inherited core and the oscillatory-zoned rim cluster at similar to 500 Ma. In summary, our preliminary geochronologic data may reflect the timing of tectonic processes in the Wilson Terrane such as (1) continuous supplies of detrital materials during the Early Cambrian; (2) the granulite facies metamorphism at similar to 500 Ma; and (3) additional thermal input at similar to 480 Ma resulting in crustal reworking.