An Archaean province in the southern Prince Charles Mountains, East Antarctica: U-Pb zircon evidence for c. 3170 Ma granite plutonism and c. 2780 Ma partial melting and orogenesis

Abstract

U-Pb ion microprobe analysis of zircon indicates that the oldest rocks from the southern Prince Charles Mountains, east Antarctica, consist of granitoid rocks of the Mawson Suite that were emplaced between 3185 and 3155 Ma. These granitoids are tectonically intercalated with the Menzies Series, a thick sequence of Cr-quartzite, marble, metaconglomerate and kyanite-bearing metapelite. Together these rocks were deformed during a single Late Archaean tectonothermal event that occurred between 2790 and 2770 Ma based on the ages of two syn-tectonic leucosomes. This event deformed the terrane via south to southwest-directed shortening and metamorphosed the rocks to upper-amphibolite facies. A sample of post-tectonic pegmatite with an age of 2645 Ma further confirms the Archaean age of deformation and metamorphism recorded by these rocks. These new age constraints demonstrate that: (1) the sialic basement (Mawson Suite + Menzies Series) of the southern Prince Charles Mountains formed entirely in the Archaean and, (2) these rocks do not share a common geologic history with the other known exposures of pre-Gondwana basement from the East Antarctic Craton, nor with the rocks of the previously continuous Gawler Craton of southern Australia. This latter point implies that the East Antarctic Craton probably did not exist as a single entity in the Archaean and Early Proterozoic, but rather formed in the Middle to Late Proterozoic via the amalgamation of a number of discrete lithospheric blocks.