Origin of the continental crust in the Colorado Plateau: Geochemical evidence from mafic xenoliths from the Navajo Volcanic Field, southwestern USA

Published geochemical and Nd, Sr, and Pb isotopic data from Proterozoic surface rocks and from NVF mafic xenoliths indicate that the crust and mantle lithosphere beneath the Colorado Plateau is dominantly Early proterozoic (2.0-1.75 Ga) in age. With the possible exception of gabbros from Moses Rock, there is no evidence among the mafic crustal xenoliths for later magmatic underplating. Incompatible element distributions are consistent with an origin for the crust by Early Proterozic arc accretion, and they do not reflect a contribution from submarine plateaus. Also, a negative Eu anomaly must exist in both the upper and lower crust in this region.