AGE OF LOW-GRADE REGIONAL METAMORPHISM IN THE NORTH GREENLAND FOLD BELT - MINERALOGICAL AND RB-SR-ISOTOPE EVIDENCE FROM PELITIC METASEDIMENTS

Established isotopic sediment-dating techniques have been used to date the time of deformation and metamorphism of the lower Palaeozoic rock s within the North Greenland fold belt. Fine mineral fractions <2 mum have been separated from pelitic sediments at widely distributed local ities and analysed using X-ray diffraction, isotope, and geochemical t echniques. The mineralogical study identified two slightly different m ineral parageneses of low greenschist facies. One assemblage without t he sodium mica paragonite is confined to calcareous lithologies of the Amundsen Land and Volvedal groups. The second assemblage includes par agonite and is found in noncalcareous lithologies of the Polkorridoren Group. Rb-Sr isotope dating of the mineral fractions yielded isochron ages in the range 318-346 Ma, which shows that final uplift and cooli ng associated with Ellesmerian tectonism in North Greenland occurred i n the Mississippian. The results suggest that, although the metamorphi sm was of regional scale, recrystallization and isotopic homogenizatio n occurred in closed systems of local extent.