Rapid determination of Pb isotopes to define Precambrian allochthonous domains: An example from West Greenland

Lacking provincial fauna, establishing autochthoneity or allochthoneity of domains in Precambrian orogens typically requires comparison of precollisional attributes across suspect terrane boundaries. We have measured the Pb isotopic compositions of K-feldspar grains in epoxy mounts and rock slabs by a rapid laser ablation-inductively coupled plasma mass spectrometry method with sufficient precision and accuracy to define two large Pb isotopic domains in the Paleoproterozoic Nagssugtoqidian-Rinkian orogen of West Greenland. These domains are interpreted to correlate with and help delineate the Rae and North Atlantic cratons. Their boundary coincides with a recently proposed location of the main collisional suture of this orogen, thus supporting this interpretation. This study validates a rapid analytical Pb isotopic method that will be useful in addressing a range of problems that requires knowledge of crustal affinity in Precambrian terrains.