Abstract

New major element, trace element, and Nd isotope data are reported for volcanic rocks from the 2.9 Ga Lower Greenstone and 2.7 Ga Upper Greenstone assemblages of the Belingwe Greenstone Belt. The majority of samples from five distinct stratigraphic units have generally unfractionated to slightly depleted trace element patterns similar to those observed in the small number of previous studies. However, previously unrecognized incompatible element–enriched samples with distinct high field strength anomalies invariably also occur in close association. These are reminiscent of crustally contaminated rocks from other well-documented greenstone settings. Numerical modeling of combined assimilation-fractionation processes using both trace and major elements suggests 10%–30% incorporation of model Archean continental crust in their genesis, in accord with Nd isotope compositions. These new observations are not consistent with a mid-ocean-ridge or oceanic plateau–type setting for Belingwe Greenstone Belt volcanism, but instead favor a model in which melts interacted with preexisting continental crust.

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