^<40>Ar-^<39>Ar GEOCHRONOLOGICAL STUDIES OF GRANITIC ROCKS FROM SOUTH VICTORIA LAND, ANTARCTICA

^Ar-^Ar ages were obtained for two granitic rocks from the Dry Valleys region of South Victoria Land, Antarctica. One sample (biotite-rich fraction) of foliated granitoid gave three age increments of 491Ma, 502Ma and 506Ma, with K/Ca ratios suggesting influence of cooling ages of biotite (younger age) and that of hornblende (older age). Granitoid emplacement is thought to have been before 506Ma, with cooling from biotite closure temperatures about 490Ma. A sample of unfoliated granitoid gave ages of 467-496Ma. The similarity of ages determined for both "pre-tectonic" and "post-tectonic" samples indicate closure of isotopic systems around 490Ma due to regional uplift/exhumation, rather than actual emplacement ages of individual plutons in South Victoria Land