Uranium-lead zircon geochronology study of the Bird River greenstone belt, southeastern Manitoba.

The Archean Bird River greenstone belt of southeastern Manitoba is in the Superior Province of the Canadian Shield. It is made up of mafic to felsic volcanic rocks and associated metasedimentary rocks. Felsic plutonic rocks intrude and surround these supracrustal rocks. To the north of the belt is the Maskwa Lake granitoid batholith which belongs the English River domain, and to the south, the belt borders with the Lac du Bonnet and Pointe du Bois granitoid batholiths of the Winnipeg River domain. The evolution of the belt and the granitoid terrains occurred over a time span of over 300 Ma, from ca. 3000 Ma to 660 Ma. U-Pb zircon ages indicate a major volcanic and plutonic event in the area in the period of 2740-2730 Ma. Age for the Lac du Bonnet batholith is 2660 $\pm$ 3 Ma. The Pointe du Bois batholith which was thought to be older than the Bird River greenstone belt, yields an age of 2729 $\pm$ 9 Ma. Two ages for the Maskwa Lake batholith indicate that this batholith must be a granitoid complex incorporating rafters of older materials; the ages are: 2725 $\pm$ 6 Ma and 2782 $\pm$ 11 Ma. The age of the supracrustal rocks is inferred to between ca. 2730 to 3000 Ma. The Peterson felsic volcanic is dated at 2740 $\pm$ 4 Ma; stratigraphically below this, the Bird River chromite sill has an age of 2745 $\pm$ 5 Ma, which is coeval and cogenetic with some of the mafic volcanism here. Sphene from a subvolcanic diorite stock of similar age yield a metamorphic age of 2715 Ma. An age of 2844 inferred for a granodiorite body adjacent to the Maskwa Lake batholith may be related to a still older volcanism here. By comparison with greenstone belts to the north and northeast, it is possible that the volcanism may be as old as 3000 Ma. However, the nature of the basement, sialic or simatic, remains unknown. Source: Masters Abstracts International, Volume: 32-06, page: 1611. Adviser: A. Turek. Thesis (M.Sc.)--University of Windsor (Canada), 1993