TIME OF METAMORPHISM BENEATH THE CENTRAL METASEDIMENTARY BELT BOUNDARY THRUST ZONE, GRENVILLE OROGEN, ONTARIO - ACCRETION AT 1080 MA

New U-Pb zircon and titanite data from the Muskoka domain, Grenville P rovince, Ontario, provide protolith and metamorphic ages for the south western Central Gneiss Belt. Discordant analyses from a migmatitic ort hogneiss and its leucosome form a linear array with an upper intercept age of 1457 +/- 6 Ma and a lower intercept age of 1064 +/- 18 Ma. U-P b analyses on metamorphic zircon from an amphibolite yield a set of co ncordant analyses with an average Pb-207/Pb-206 age of 1079 +/- 3 Ma. A weakly migmatitic granitoid rock and a transecting charnockitic vein in the immediate footwall of the Central Metasedimentary Belt boundar y thrust zone yielded a discordant array of analyses with an upper int ercept age of 1394 +/- 13 Ma and a lower intercept age of 1066 +/- 8 M a. The charnockitic vein yielded concordant zircon ages of 1077 +/- 2 Ma. The upper intercept ages are interpreted in terms of protolith cry stallization, and the concordant and lower intercept ages as Grenvilli an high-grade metamorphism and associated anatexis. We have found no e vidence for a ca. 1190-1160 Ma metamorphic event in these rocks, as re quired by some regional tectonic interpretations. We conclude that emp lacement of the Central Metasedimentary Belt over the Central Gneiss B elt, which caused high-grade metamorphism in the Muskoka domain, occur red at or shortly before ca. 1080 Ma, and that this marks the time of accretion of the Central Metasedimentary Belt to the southeast margin of Laurentia.