Behavior of the U-Pb system in monazite and chronology of metasedimentary deformation and metamorphism in the Kisseynew Domain of the Trans Hudson Orogen in Manitoba (Canada)

The Kisseynew domain is the central unit of the Reindeer Zone of the Paleop roterozoic Trans-Hudson Orogen, in Manitoba and Saskatchewan. The southern flank of the domain is a transition zone between the greenschist facies of the volcano-plutonic assemblage of the Flin Flon - Snow Lake belt and the u pper amphibolite facies of Kisseynew paragneisses. The Jungle Lake area, in the southern flank of the Kisseynew Domain, comprises mainly quartzofeldsp athic gneisses representing continental clastic units of the Missi suite an d migmatitic metagraywackes of the Burntwood suite. The area was affected b y several phases of deformation, metamorphism, and migmatisation. Detailed mapping and U-Pb geochronology were carried out in order to establish the t iming of the deformational and metamorphic phases. The oldest leucosome con tains sillimanite formed during peak metamorphism and is associated with F2 folding and S2 fabric. Five single monazites from this leucosome yield age s between 1809 and 1803 Ma taken as the best estimate for the duration of p eak metamorphism. Biotite schlieren in diatexites in the Burntwood suite sh ow a S2 fabric folded by F3. Zircon from one of these diatexites yield a cr ystallization age of 1798(-2)(+3) Ma, considered as the lower limit for the F2 event. Single monazites from the same rock yield ages between 1812 and 1789 Ma, the oldest of which are considered to be inherited. The youngest m obilisate is a pegmatite crosscutting F2 and F3 fabrics and yielded single monazite ages between 1875 and 1788 Ma. The youngest age is taken as the ag e of the pegmatite and is a minimum age for F3 fabrics. These results, toge ther with those from other areas of the southern Kisseynew Domain, indicate a ca. 30 million year period (1818 and 1785 Ma) of continuous deformation and metamorphism. The data also show the presence of monazite crystals of d ifferent ages in the same rock illustrating the need to analyse single grai ns to obtain geologically meaningful ages.