Comportement du système U-Pb dans la monazite et chronolgie de la déformation et du métamorphisme des metasédiments du domaine de Kisseynew, orogène trans- hudsonien (Manitoba, Canada)

摘要

The Kisseynew domain is the central unit of theReindeer Zone of the Paleoproterozoic Trans-Hudson Orogen,in Manitoba and Saskatchewan. The southern flank of thedomain is a transition zone between the greenschist facies of thevolcano-plutonic assemblage of the Flin Flon - Snow Lake beltand the upper amphibolite facies of Kisseynew paragneisses.The Jungle Lake area, in the southern flank of the KisseynewDomain, comprises mainly quartzofeldspathic gneissesrepresenting continental clastic units of the Missi suite andmigmatitic metagraywackes of the Burntwood suite. The areawas affected by several phases of deformation, metamorphism,and migmatisation. Detailed mapping and U-Pb geochronologywere carried out in order to establish the timing of thedeformational and metamorphic phases. The oldest leucosomecontains sillimanite formed during peak metamorphism and isassociated with F2 folding and S2 fabric. Five single monazitesfrom this leucosome yield ages between 1809 and 1803 Mataken as the best estimate for the duration of peakmetamorphism. Biotite schlieren in diatexites in the Burntwoodsuite show a S2 fabric folded by F3. Zircon from one of thesediatexites yield a crystallization age of 1798_(-2)~(+3) Ma,considered as the lower limit for the F2 event. Single monazitesfrom the same rock yield ages between 1812 and 1789 Ma, theoldest of which are considered to be inherited. The youngestmobilisate is a pegmatite crosscutting F2 and F3 fabrics andyielded single monazite ages between 1875 and 1788 Ma. Theyoungest age is taken as the age of the pegmatite and is aminimum age for F3 fabrics. These results, together with thosefrom other areas of the southern Kisseynew Domain, indicate aca. 30 million year period (1818 and 1785 Ma) of continuousdeformation and metamorphism. The data also show thepresence of monazite crystals of different ages in the same rockillustrating the need to analyse single grains to obtaingeologically meaningful ages.