Geological significance of U-Pb and Rb-Sr ages from two pre- tectonic granites from the Central Metasedimentary Belt, Ontario ( Canada).

The geologic history of two granitoid units has been investigated by comparing U-Pb zircon, U-Pb sphene (titanite) and Rb-Sr whole rock ages determined on samples collected from the same site. Except for the emplacement of granitic magma at approx 1250 Ma, the geological events recorded in the study area are not reflected in a compilation of U-Pb zircon and Rb-Sr whole rock data presently available for other granitoid units from the Central Metasedimentary Belt. Initial Sr ratios for these granitoid units indicate insignificant involvement of older upper crustal material in the generation of thes rocks, implying lower crust or mantle derivation.-from Authors