Age of low-grade regional metamorphism in the North Greenland fold belt: mineralogical and Rb–Sr-isotope evidence from pelitic metasediments

Abstract

Established isotopic sediment-dating techniques have been used to date the time of deformation and metamorphism of the lower Palaeozoic rocks within the North Greenland fold belt. Fine mineral fractions < 2 μm have been separated from pelitic sediments at widely distributed localities and analysed using X-ray diffraction, isotope, and geochemical techniques.The mineralogical study identified two slightly different mineral parageneses of low greenschist facies. One assemblage without the sodium mica paragonite is confined to calcareous lithologies of the Amundsen Land and Vølvedal groups. The second assemblage includes paragonite 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 cooling associated with Ellesmerian tectonism in North Greenland occurred in the Mississippian. The results suggest that, although the metamorphism was of regional scale, recrystallization and isotopic homogenization occurred in closed systems of local extent.