Nd and Sr isotopic compositions of tektite material from Barbados and their relationship to North American tektites

Abstract

Isotopic analyses of Nd and Sr on individual microtektites and a bulk microtektite sample from Barbados show them to have a very well defined isotopic composition. These data plot on an ε Srε Nd diagram precisely within the narrow field determined by North American tektites (ε Sr ≈ 111; ε Nd ≈ −6.2). They yield an Nd model age of 0.6 AE. These results show that the microtektites from the Oceanic beds of late Eocene age are derived from the same target as the North American tektites and should be associated with the same event. Samples of the deep sea sediments in which the Barbados microtektites occur are found to have isotopic signatures which appear to reflect ambient sea water and detrital sediments. They cannot be the source of Sr or Nd in the tektites. Following the arguments of Shaw and Wasserburg (1982) we conclude that the target area which produced the North American tektite field was composed of sediments (Eocambrian or younger) derived from very late Precambrian crust. Glass beads from Lake Wanapitei Crater are isotopically different from all other tektites (ε Sr ≈ 960; ε Nd ≈ −31.4) and cannot be related to the North American tektites.