2.5 b.y. of punctuated Earth history as recorded in a single rock

Deciphering the absolute chronology of ancient crustal rocks is often problematical because of isotopic reequilibration and/or mixing during multiple geologic events. Ion probe U-Pb age data from texturally distinct zircon crystal domains in a single sample of high-grade gneiss from the Nimrod Group in Antarctica reflect successive resorption and crystallization under disequilibrium conditions. Our data indicate that Archean crust of the East Antarctic shield, initially formed from juvenile magmas ca. 3000 Ma, extends to the central Transantarctic Mountains. Successive zircon growth ca. 2955, 1720, and 530 Ma records a sequence of distinct, widely spaced high-temperature metamorphic and/or anatectic events related to Archean, Paleoproterozoic, and Eocambrian orogenesis.