A model for Sr evolution in the West Greenland-Labrador region is proposed based on the available data for granitic gneisses ranging in age from 3.6 AE to 1.9 AE and for recent continental tholeiites from West Greenland. The evolution of initial Sr isotopic composition is consistent with a two-stage model for the mantle in this area with a constant Rb/Sr ratio of 0.014 ± 0.002 from ∼ 4.45 AE through the present. The model suggests the mantle may have been depleted in Rb ∼ 4.45 AE ago if the Earth was originally chondritic with respect to Rb and Sr. This age of differentiation is consistent with recently proposed terrestrial differentiation based on Pb Pb analyses of ancient Amîtsoq gneiss feldspars (∼4.47 AE, Gancarz and Wasserburg, 1977). A linear regression of the gneisses, if extrapolated to the present, predicts the present value of Sr 87/Sr 86 of the mantle in this area to be 0.7034 ± 0.0003 which is the measured Sr isotopic composition of the recent Svartenhuk tholeiites. Various implications of the model with respect to early Earth history, mantle evolution and pre-emplacement histories of gneissic suites are discussed.