ZIRCON U-PB GEOCHRONOLOGY OF PLUTONIC ROCKS FROM THE ANTARCTIC PENINSULA - CONFIRMATION OF THE PRESENCE OF UNEXPOSED PALEOZOIC CRUST

The Antarctic Peninsula represents the southernmost segment of a magma tic are once present along the western margin of Gondwanaland. Zircon U-Pb geochronology of a suite of calc-alkaline granitoids from the wes t coast of Graham Land, northern Antarctic Peninsula, resulted in ages for the rocks ranging from 117.0 +/- 0.8 to 73.6 +/- 0.4 Ma. Discorda nt zircon populations from peraluminous granites reveal inheritance ch aracteristics resulting from entrainnent of older crustal materials. U pper intercept ages of discordant zircon populations in four samples i ndicate that the age of assimilated material is approximately late Pal eozoic. This inherited component is present in four samples from Bone Bay, Charlotte Bay, and Stonington Island and thus may extend for simi lar to 600 km along the west coast of Graham Land. A possible source f or the inherited components is the late Paleozoic(?) sediments of the Trinity Peninsula Group. However, a late Proterozoic upper intercept a ge for the Charlotte Bay granodiorite in western central Graham Land i ndicates that the age of the rocks assimilated by this suite of pluton s is not uniformly late Paleozoic and might include unexposed basement rocks. Finally, an upper intercept age of 431 +/- 12 Ma from a granit e clast in metaconglomerate from Horseshoe Island provides further evi dence for the presence of midpaleozoic basement in Graham Land. These results confirm the already postulated minimum early Paleozoic age for Antarctic Peninsula basement.