THE PARRY SOUND DOMAIN - A FAR-TRAVELED ALLOCHTHON - NEW EVIDENCE FROM U-PB ZIRCON GEOCHRONOLOGY

We report U-Pb zircon ages for metaplutonic and metasedimentary rocks from three lithotectonic assemblages within the Parry Sound allochthon of the Central Gneiss Belt, southwestern Grenville Orogen: the basal Parry Sound, interior Parry Sound, and Twelve Mile Bay assemblages. Ma gmatic crystallization ages for granitic to tonalitic gneisses from th e basal Parry Sound assemblage fall in the range 1400-1330 Ma. Younger intrusions include the Parry Island anorthosite dated at 1163 +/- 3 M a and a crosscutting mafic dyke bracketed between 1151 and 1163 Ma. Da ted at 1314(-9)(+12) Ma, a tonalitic gneiss from the overlying interio r Parry Sound assemblage is slightly younger than the older group of r ocks from the basal Parry Sound assemblage. Pb-207/Pb-206 ages for zir cons from a quartzite of the basal Parry Sound assemblage range from 1 385 Ma to the Neoarchaean. An absolute maximum age for this quartzite is 1436 +/- 17 Ma. In contrast, detrital zircons from a quartzite of t he Twelve Mile Bay assemblage constrain the age of deposition at post- ca. 1140-1120 Ma. We speculate that Grenvillian-age zircons within thi s quartzite were derived from rocks in the Adirondack Highlands and Fr ontenac terrane, implying that part of the Parry Sound domain and thes e terranes were contiguous during deposition of the quartzite. Our dat a support previous interpretations that the Parry Sound domain is allo chthonous with respect to its surroundings, and suggest that the most likely source region of the basal Parry Sound domain lies southeast of the Central Gneiss Belt, within the Central Metasedimentary Belt boun dary thrust zone or the Adirondack Highlands. This implies the possibi lity of 100-300 km of displacement of the domain. Emplacement of the P arry Sound domain into its present position must have occurred relativ ely late in the orogen's history, by about 1080 Ma.