U-PB AGES FOR MAGMATISM AND DEFORMATION IN THE NEW QUEBEC OROGEN

The New Quebec Orogen is a Paleoproterozoic fold and thrust belt, acti ve from 2.17 to 1.77 Ga, bordering the eastern margin of the Archean S uperior Province. The orogen developed on a long-lived, passive contin ental margin and comprises two volcanic-sedimentary sequences. The age s presented in this study help to bracket the magmatic and deformation al history of the orogen. A glomeroporphyritic gabbro from the Hellanc ourt Formation was dated at 1874 +/- 3 Ma and a rhyodacite from the up per Murdoch Formation yielded an identical age of 1870 +/- 4 Ma. These data allow the correlation of the two units and indicate that they ar e 10-14 Ma younger than the estimated age for the Sokoman Formation. T hese ages, together with already published work, indicate that magmati sm related to the younger magmatic event occurred at 1884-1870 Ma. Alb itized pelites from the Murdoch Formation contain euhedral detrital zi rcons 2707-2690 Ma old, indicating that the source rocks were Archean. An undeformed monzonitic intrusion occurring close to Nachicapau Lake is 1813 +/- 4 Ma old and is the lower limit for the age of deformatio n in the central sector of the orogen.