U-Pb geochronology of the Cain Domain and the uraniferous Baker Domain, Central Metasedimentary Belt, Mont-Laurier region, Grenville Province
Suzie Nantel (MRNF), Donald W. Davis (U of T), Jean David (GEOTOP– UQAM –McGill)

The Cain Domain is bordered to the west by the Central Metasedimentary Belt Boundary Zone and to the east by the Lièvre shear zone. The latter also marks the western limit of the uraniferous Baker Domain, the eastern limit of which is marked by the Labelle shear zone. The metasedimentary rocks of these two domains consist of aluminous and micaceous paragneiss, quartzite, marble and calc-silicate rocks. The Baker Domain is distinguished by the presence of tourmaline-rich rocks, metapelites with nodules of fibrolite and muscovite, abundant feldspathic paragneiss, and uraniferous pegmatites. Based on detrital zircon ages, the most common source for metasedimentary rocks in the uraniferous Baker Domain is of Paleoproterozoic age (1846 Ma), whereas a Mesoproterozoic source (1427 Ma) dominates rocks of the Cain Domain and the Paleoproterozoic source is minor.

Mafic and tonalitic sills of the Lacoste Intrusive Suite were emplaced in Baker Domain metasedimentary rocks. The suite belongs to a continental magmatic arc with zircon ages of 1450±10 Ma and 1365±2 Ma. In the Cain Domain, where such sills are absent, the Lacoste Intrusive Suite is represented by tonalite plutons for which a sample yielded a Nd model age of 1.38 Ga and a magmatic zircon age of 1386±18 Ma. An orthogneiss from the Béthune Magmatic Suite, which caused contact metamorphism of the host Cain Domain marbles, yielded a magmatic zircon age of 1282±15 Ma. A metamorphic overprint of 1.16 Ga, based on the ages of monazites in orthogneisses of the Béthune Magmatic Suite and zircons from a tonalite in the Lacoste Intrusive Suite, is contemporaneous with the emplacement of monzonites, diorites and gabbros of the Chevreuil Intrusive Suite. A minette dyke and a monzonite pluton of the Kensington-Skootamatta Alkaline Suite provided magmatic zircon ages of 1080±2 Ma and 1071±1 Ma, respectively. The most recent magmatic event is marked by an intrusion and dykes of monzonite, quartz monzonite and syenite, with Cu-Au-Ag mineralization. These rocks belong to the Lesueur Alkaline Suite that was dated at 1000±6 Ma using zircons. Uraniferous dykes may also be related to this suite (Niogold, 2007/09/11).

The Brockaby Suite comprises metatexites, schlieren diatexites and massive diatexites. These rocks, outcrops of which are virtually restricted to the uraniferous Baker Domain, represent a major anatectic event at 1067±1 Ma based on the age of a massive diatexite. In the Baker Domain, metamorphic ages of 1084-1031 Ma (zircon) and 1083-1060 Ma (titanite) are attributed to the Ottawan phase of the Grenvillian orogeny. Finally, titanite ages of 1009-987 Ma suggest late-stage metamorphic activity in this domain.