Uranium-lead geochronology of the Archean Imataca Series,Venezuelan Guayana Shield

Uranium and lead isotopic analyses of total-rock and feldspar samples from the Imataca Series indicate an early Archean (3.5⁺ b.y.) age for the basement gneisses. Lead isotopic evolution in most gneiss samples may approximately be described by a three-stage model. The start of the third stage is marked by a pervasive metamorphic event, locally up to pyroxene-granulite grade, at 2 b.y. ago, which commonly resulted in extensive depletion of uranium relative to lead.