Use of Rb-Sr isotope data to constrain the time of deposition of Precambrian metasediments: an example from Hamborgerland, West Greenland

Abstract

In high-grade metamorphic terrains it is often not possible to determine the relative age of metasedimentary units by field investigation. However, the time of deposition of the original sediment can be constrained by consideration of the Sr-isotopic evolution of the rocks on the scale of an outcrop. An outline of the method is given, and Rb-Sr data for high-grade (granulite facies) metasediments from HamborgerIand, West Greenland, are discussed as an example. Sm-Nd model age data indicate that these rocks were derived by erosion of a 3000–3200 Ma basement. Deposition took place not long before 2700 Ma ago, and closure of the Rb-Sr isotope system after high-grade metamorphism occurred at about 2600 Ma.