U–Pb ages for magmatism and deformation in the New Quebec Orogen

Abstract

The New Quebec Orogen is a Paleoproterozoic fold and thrust belt, active from 2.17 to 1.77 Ga, bordering the eastern margin of the Archean Superior Province. The orogen developed on a long-lived, passive continental margin and comprises two volcanic – sedimentary sequences. The ages presented in this study help to bracket the magmatic and deformational history of the orogen. A glomeroporphyritic gabbro from the Hellancourt Formation was dated at 1874 ± 3 Ma and a rhyodacite from the upper Murdoch Formation yielded an identical age of 1870 ± 4 Ma. These data allow the correlation of the two units and indicate that they are 10–14 Ma younger than the estimated age for the Sokoman Formation. These ages, together with already published work, indicate that magmatism related to the younger magmatic event occurred at 1884–1870 Ma. Albitized pelites from the Murdoch Formation contain euhedral detrital zircons 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 deformation in the central sector of the orogen.